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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
A T(1) theorem for Sobolev spaces on domainsPHD thesis in progress, directed by Xavier Tolsa
Martı Prats
Universitat Autonoma de Barcelona
September 19, 2013
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Introduction
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The Beurling transform
The Beurling transform of a function f ∈ Lp(C) is:
Bf (z) = c0 limε→0
ˆ|w−z|>ε
f (w)
(z − w)2dm(z).
It is essential to quasiconformal mappings because
B(∂f ) = ∂f ∀f ∈W 1,p.
Recall that B : Lp(C)→ Lp(C) is bounded for 1 < p <∞.Also B : W s,p(C)→W s,p(C) is bounded for 1 < p <∞ and s > 0.
In particular, if z /∈ supp(f ) then Bf is analytic in an ε-neighborhood ofz and
∂nBf (z) = cn
ˆ|w−z|>ε
f (w)
(z − w)n+2dm(z).
back to T(P)
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The Beurling transform
The Beurling transform of a function f ∈ Lp(C) is:
Bf (z) = c0 limε→0
ˆ|w−z|>ε
f (w)
(z − w)2dm(z).
It is essential to quasiconformal mappings because
B(∂f ) = ∂f ∀f ∈W 1,p.
Recall that B : Lp(C)→ Lp(C) is bounded for 1 < p <∞.Also B : W s,p(C)→W s,p(C) is bounded for 1 < p <∞ and s > 0.
In particular, if z /∈ supp(f ) then Bf is analytic in an ε-neighborhood ofz and
∂nBf (z) = cn
ˆ|w−z|>ε
f (w)
(z − w)n+2dm(z).
back to T(P)
![Page 5: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/5.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The Beurling transform
The Beurling transform of a function f ∈ Lp(C) is:
Bf (z) = c0 limε→0
ˆ|w−z|>ε
f (w)
(z − w)2dm(z).
It is essential to quasiconformal mappings because
B(∂f ) = ∂f ∀f ∈W 1,p.
Recall that B : Lp(C)→ Lp(C) is bounded for 1 < p <∞.Also B : W s,p(C)→W s,p(C) is bounded for 1 < p <∞ and s > 0.
In particular, if z /∈ supp(f ) then Bf is analytic in an ε-neighborhood ofz and
∂nBf (z) = cn
ˆ|w−z|>ε
f (w)
(z − w)n+2dm(z).
back to T(P)
![Page 6: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/6.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The Beurling transform
The Beurling transform of a function f ∈ Lp(C) is:
Bf (z) = c0 limε→0
ˆ|w−z|>ε
f (w)
(z − w)2dm(z).
It is essential to quasiconformal mappings because
B(∂f ) = ∂f ∀f ∈W 1,p.
Recall that B : Lp(C)→ Lp(C) is bounded for 1 < p <∞.Also B : W s,p(C)→W s,p(C) is bounded for 1 < p <∞ and s > 0.
In particular, if z /∈ supp(f ) then Bf is analytic in an ε-neighborhood ofz and
∂nBf (z) = cn
ˆ|w−z|>ε
f (w)
(z − w)n+2dm(z).
back to T(P)
![Page 7: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/7.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The problem we face
Let Ω be a Lipschitz domain.
When is B : W s,p(Ω)→W s,p(Ω) bounded?We want an answer in terms of the geometry of the boundary.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Known facts, part 1
In a recent paper, Cruz, Mateu and Orobitg proved that for 0 < s ≤ 1,2 < p <∞ with sp > 2, and ∂Ω smooth enough,
Theorem
B : W s,p(Ω)→W s,p(Ω) is bounded
if and only ifBχΩ ∈W s,p(Ω).
One can deduce regularity of a quasiregular mappingin terms of the regularity of its Beltrami coefficient.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Known facts, part 1
In a recent paper, Cruz, Mateu and Orobitg proved that for 0 < s ≤ 1,2 < p <∞ with sp > 2, and ∂Ω smooth enough,
Theorem
B : W s,p(Ω)→W s,p(Ω) is bounded
if and only ifBχΩ ∈W s,p(Ω).
One can deduce regularity of a quasiregular mappingin terms of the regularity of its Beltrami coefficient.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Introducing the Besov spaces B sp,p
The geometric answer will be given in terms of Besov spaces Bsp,p.
Bsp,p form a family closely related to W s,p. They coincide for p = 2.
For p < 2, Bsp,p ⊂W s,p. Otherwise W s,p ⊂ Bs
p,p.
Definition
For 0 < s <∞, 1 ≤ p <∞, f ∈ Bsp,p(R) if
‖f ‖Bsp,p
=
(ˆR
ˆR
∣∣∣∣∣∆[s]+1h f (x)
hs
∣∣∣∣∣pdm(h)
|h|dm(x)
)1/p
<∞.
Furthermore, f ∈ Bsp,p(R) if
‖f ‖Bsp,p
= ‖f ‖Lp + ‖f ‖Bsp,p<∞.
We call them homogeneous and non-homogeneous Besov spacesrespectively.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Introducing the Besov spaces B sp,p
The geometric answer will be given in terms of Besov spaces Bsp,p.
Bsp,p form a family closely related to W s,p. They coincide for p = 2.
For p < 2, Bsp,p ⊂W s,p. Otherwise W s,p ⊂ Bs
p,p.
Definition
For 0 < s <∞, 1 ≤ p <∞, f ∈ Bsp,p(R) if
‖f ‖Bsp,p
=
(ˆR
ˆR
∣∣∣∣∣∆[s]+1h f (x)
hs
∣∣∣∣∣pdm(h)
|h|dm(x)
)1/p
<∞.
Furthermore, f ∈ Bsp,p(R) if
‖f ‖Bsp,p
= ‖f ‖Lp + ‖f ‖Bsp,p<∞.
We call them homogeneous and non-homogeneous Besov spacesrespectively.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Introducing the Besov spaces B sp,p
The geometric answer will be given in terms of Besov spaces Bsp,p.
Bsp,p form a family closely related to W s,p. They coincide for p = 2.
For p < 2, Bsp,p ⊂W s,p. Otherwise W s,p ⊂ Bs
p,p.
Definition
For 0 < s <∞, 1 ≤ p <∞, f ∈ Bsp,p(R) if
‖f ‖Bsp,p
=
(ˆR
ˆR
∣∣∣∣∣∆[s]+1h f (x)
hs
∣∣∣∣∣pdm(h)
|h|dm(x)
)1/p
<∞.
Furthermore, f ∈ Bsp,p(R) if
‖f ‖Bsp,p
= ‖f ‖Lp + ‖f ‖Bsp,p<∞.
We call them homogeneous and non-homogeneous Besov spacesrespectively.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Known facts, part 2
In another recent paper, Cruz and Tolsa proved that for any 1 < p <∞,and Ω a Lipschitz domain,
Theorem
If the normal vector N belongs to B1−1/pp,p (∂Ω), then B(χΩ) ∈W 1,p(Ω)
with‖∇B(χΩ)‖Lp(Ω) ≤ c‖N‖
B1−1/pp,p (∂Ω)
.
They proved also an analogous result for smoothness 0 < s < 1.This implies
Theorem
Let 0 < s ≤ 1, 2 < p <∞ with sp > 2. If the normal vector
is in the Besov space Bs−1/pp,p (∂Ω), then the Beurling transform
is bounded in W s,p(Ω).
Tolsa proved a converse for Ω flat enough.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Known facts, part 2
In another recent paper, Cruz and Tolsa proved that for any 1 < p <∞,and Ω a Lipschitz domain,
Theorem
If the normal vector N belongs to B1−1/pp,p (∂Ω), then B(χΩ) ∈W 1,p(Ω)
with‖∇B(χΩ)‖Lp(Ω) ≤ c‖N‖
B1−1/pp,p (∂Ω)
.
They proved also an analogous result for smoothness 0 < s < 1.
This implies
Theorem
Let 0 < s ≤ 1, 2 < p <∞ with sp > 2. If the normal vector
is in the Besov space Bs−1/pp,p (∂Ω), then the Beurling transform
is bounded in W s,p(Ω).
Tolsa proved a converse for Ω flat enough.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Known facts, part 2
In another recent paper, Cruz and Tolsa proved that for any 1 < p <∞,and Ω a Lipschitz domain,
Theorem
If the normal vector N belongs to B1−1/pp,p (∂Ω), then B(χΩ) ∈W 1,p(Ω)
with‖∇B(χΩ)‖Lp(Ω) ≤ c‖N‖
B1−1/pp,p (∂Ω)
.
They proved also an analogous result for smoothness 0 < s < 1.This implies
Theorem
Let 0 < s ≤ 1, 2 < p <∞ with sp > 2. If the normal vector
is in the Besov space Bs−1/pp,p (∂Ω), then the Beurling transform
is bounded in W s,p(Ω).
Tolsa proved a converse for Ω flat enough.
![Page 16: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/16.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Known facts, part 2
In another recent paper, Cruz and Tolsa proved that for any 1 < p <∞,and Ω a Lipschitz domain,
Theorem
If the normal vector N belongs to B1−1/pp,p (∂Ω), then B(χΩ) ∈W 1,p(Ω)
with‖∇B(χΩ)‖Lp(Ω) ≤ c‖N‖
B1−1/pp,p (∂Ω)
.
They proved also an analogous result for smoothness 0 < s < 1.This implies
Theorem
Let 0 < s ≤ 1, 2 < p <∞ with sp > 2. If the normal vector
is in the Besov space Bs−1/pp,p (∂Ω), then the Beurling transform
is bounded in W s,p(Ω).
Tolsa proved a converse for Ω flat enough.
![Page 17: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/17.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Main results
T(P) Theorem
Let 2 < p <∞ and 1 ≤ n <∞. Let Ω be a Lipschitz domain.Then the Beurling transform is bounded in W n,p(Ω)if and only if for any polynomial of degree less than nrestricted to the domain, P = PχΩ, B(P) ∈W n,p(Ω).
This theorem is valid for any Calderon-Zygmund convolution operatorwith enough smoothness and for any space Rd .
Theorem (Geometric condition on the boundary)
Let Ω be smooth enough. Then we can write
‖∂nBχΩ‖pLp(Ω) . ‖N‖p
Bn−1/pp,p (∂Ω)
+H1(∂Ω)2−np.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Main results
T(P) Theorem
Let 2 < p <∞ and 1 ≤ n <∞. Let Ω be a Lipschitz domain.Then the Beurling transform is bounded in W n,p(Ω)if and only if for any polynomial of degree less than nrestricted to the domain, P = PχΩ, B(P) ∈W n,p(Ω).
This theorem is valid for any Calderon-Zygmund convolution operatorwith enough smoothness and for any space Rd .
Theorem (Geometric condition on the boundary)
Let Ω be smooth enough. Then we can write
‖∂nBχΩ‖pLp(Ω) . ‖N‖p
Bn−1/pp,p (∂Ω)
+H1(∂Ω)2−np.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Main results
T(P) Theorem
Let 2 < p <∞ and 1 ≤ n <∞. Let Ω be a Lipschitz domain.Then the Beurling transform is bounded in W n,p(Ω)if and only if for any polynomial of degree less than nrestricted to the domain, P = PχΩ, B(P) ∈W n,p(Ω).
This theorem is valid for any Calderon-Zygmund convolution operatorwith enough smoothness and for any space Rd .
Theorem (Geometric condition on the boundary)
Let Ω be smooth enough. Then we can write
‖∂nBχΩ‖pLp(Ω) . ‖N‖p
Bn−1/pp,p (∂Ω)
+H1(∂Ω)2−np.
![Page 20: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/20.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Proof of the T(P) Theorem
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts
Beurling transform
We have a Lipschitz domain.
In particular, at every boundary pointwe can center a cubewith fixed side-length Rinducing a parametrization C 0,1.
We make a covering of the boundaryby N of such cubes Qk
with some controlled overlappingand find a partition of unity ψjNj=0.
‖Bf ‖pW n,p(Ω) ≈ ‖Bf ‖pLp(Ω) + ‖∇nBf ‖pLp(Ω).
‖∇nBf ‖pLp(Ω) ≈∑N
k=0 ‖∇nB(f ψk)‖pLp(Qk ) + ‖∇nB(f ψk)‖pLp(Ω\Qk )
Away from Qk we have good bounds:|∇nB(f ψk)(z)| . 1
Rn+2
´Qk|f (w)|dw
The restriction to the inner region is always bounded:f ψ0 ∈W n,p(C).
![Page 22: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/22.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts
Beurling transform
We have a Lipschitz domain.
In particular, at every boundary pointwe can center a cubewith fixed side-length Rinducing a parametrization C 0,1.
We make a covering of the boundaryby N of such cubes Qk
with some controlled overlappingand find a partition of unity ψjNj=0.
‖Bf ‖pW n,p(Ω) ≈ ‖Bf ‖pLp(Ω) + ‖∇nBf ‖pLp(Ω).
‖∇nBf ‖pLp(Ω) ≈∑N
k=0 ‖∇nB(f ψk)‖pLp(Qk ) + ‖∇nB(f ψk)‖pLp(Ω\Qk )
Away from Qk we have good bounds:|∇nB(f ψk)(z)| . 1
Rn+2
´Qk|f (w)|dw
The restriction to the inner region is always bounded:f ψ0 ∈W n,p(C).
![Page 23: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/23.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts
Beurling transform
We have a Lipschitz domain.
In particular, at every boundary pointwe can center a cubewith fixed side-length Rinducing a parametrization C 0,1.
We make a covering of the boundaryby N of such cubes Qk
with some controlled overlappingand find a partition of unity ψjNj=0.
‖Bf ‖pW n,p(Ω) ≈ ‖Bf ‖pLp(Ω) + ‖∇nBf ‖pLp(Ω).
‖∇nBf ‖pLp(Ω) ≈∑N
k=0 ‖∇nB(f ψk)‖pLp(Qk ) + ‖∇nB(f ψk)‖pLp(Ω\Qk )
Away from Qk we have good bounds:|∇nB(f ψk)(z)| . 1
Rn+2
´Qk|f (w)|dw
The restriction to the inner region is always bounded:f ψ0 ∈W n,p(C).
![Page 24: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/24.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts
Beurling transform
We have a Lipschitz domain.
In particular, at every boundary pointwe can center a cubewith fixed side-length Rinducing a parametrization C 0,1.
We make a covering of the boundaryby N of such cubes Qk
with some controlled overlappingand find a partition of unity ψjNj=0.
‖Bf ‖pW n,p(Ω) ≈ ‖Bf ‖pLp(Ω) + ‖∇nBf ‖pLp(Ω).
‖∇nBf ‖pLp(Ω) ≈∑N
k=0 ‖∇nB(f ψk)‖pLp(Qk ) + ‖∇nB(f ψk)‖pLp(Ω\Qk )
Away from Qk we have good bounds:|∇nB(f ψk)(z)| . 1
Rn+2
´Qk|f (w)|dw
The restriction to the inner region is always bounded:f ψ0 ∈W n,p(C).
![Page 25: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/25.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts
Beurling transform
We have a Lipschitz domain.
In particular, at every boundary pointwe can center a cubewith fixed side-length Rinducing a parametrization C 0,1.
We make a covering of the boundaryby N of such cubes Qk
with some controlled overlappingand find a partition of unity ψjNj=0.
‖Bf ‖pW n,p(Ω) ≈ ‖Bf ‖pLp(Ω) + ‖∇nBf ‖pLp(Ω).
‖∇nBf ‖pLp(Ω) ≈∑N
k=0 ‖∇nB(f ψk)‖pLp(Qk ) + ‖∇nB(f ψk)‖pLp(Ω\Qk )
Away from Qk we have good bounds:|∇nB(f ψk)(z)| . 1
Rn+2
´Qk|f (w)|dw
The restriction to the inner region is always bounded:f ψ0 ∈W n,p(C).
![Page 26: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/26.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts
Beurling transform
We have a Lipschitz domain.
In particular, at every boundary pointwe can center a cubewith fixed side-length Rinducing a parametrization C 0,1.
We make a covering of the boundaryby N of such cubes Qk
with some controlled overlappingand find a partition of unity ψjNj=0.
‖Bf ‖pW n,p(Ω) ≈ ‖Bf ‖pLp(Ω) + ‖∇nBf ‖pLp(Ω).
‖∇nBf ‖pLp(Ω) ≈∑N
k=0 ‖∇nB(f ψk)‖pLp(Qk ) + ‖∇nB(f ψk)‖pLp(Ω\Qk )
Away from Qk we have good bounds:|∇nB(f ψk)(z)| . 1
Rn+2
´Qk|f (w)|dw
The restriction to the inner region is always bounded:f ψ0 ∈W n,p(C).
![Page 27: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/27.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts
Beurling transform
We have a Lipschitz domain.
In particular, at every boundary pointwe can center a cubewith fixed side-length Rinducing a parametrization C 0,1.
We make a covering of the boundaryby N of such cubes Qk
with some controlled overlappingand find a partition of unity ψjNj=0.
‖Bf ‖pW n,p(Ω) ≈ ‖Bf ‖pLp(Ω) + ‖∇nBf ‖pLp(Ω).
‖∇nBf ‖pLp(Ω) ≈∑N
k=0 ‖∇nB(f ψk)‖pLp(Qk ) + ‖∇nB(f ψk)‖pLp(Ω\Qk )
Away from Qk we have good bounds:|∇nB(f ψk)(z)| . 1
Rn+2
´Qk|f (w)|dw
The restriction to the inner region is always bounded:f ψ0 ∈W n,p(C).
![Page 28: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/28.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Whitney decomposition
We perform an oriented Whitney covering W such that
dist(Q, ∂Ω ∩Q) ≈ `(Q) for every Q ∈ W.
The family 5QQ∈W has finite superposition.
...
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Whitney decomposition
We perform an oriented Whitney covering W such that
dist(Q, ∂Ω ∩Q) ≈ `(Q) for every Q ∈ W.
The family 5QQ∈W has finite superposition.
...
![Page 30: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/30.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Whitney decomposition
We perform an oriented Whitney covering W such that
dist(Q, ∂Ω ∩Q) ≈ `(Q) for every Q ∈ W.
The family 5QQ∈W has finite superposition.
...
![Page 31: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/31.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
A necessity arises: approximating polynomials
We will use the Poincare inequality, that is, given f ∈W 1,p(Q),1 ≤ p ≤ ∞,
‖f −mQ f ‖Lp(Q) . `(Q)‖∇f ‖Lp(Q).
Equivalently, for any Sobolev function f with 0 mean on Q,
‖f ‖Lp(Q) . `(Q)‖∇f ‖Lp(Q).
If we want to apply recursively the Poincare inequality we need Df tohave mean 0 in 3Q for any partial derivative D.
Definition
Given f ∈W n,p(Ω) and a cube Q, we call PnQ f to the polynomial ofdegree smaller than n restricted to Ω such that for any multiindex β with|β| < n,
3Q
DβPnQ f =
3Q
Dβf .
![Page 32: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/32.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
A necessity arises: approximating polynomials
We will use the Poincare inequality, that is, given f ∈W 1,p(Q),1 ≤ p ≤ ∞,
‖f −mQ f ‖Lp(Q) . `(Q)‖∇f ‖Lp(Q).
Equivalently, for any Sobolev function f with 0 mean on Q,
‖f ‖Lp(Q) . `(Q)‖∇f ‖Lp(Q).
If we want to apply recursively the Poincare inequality we need Df tohave mean 0 in 3Q for any partial derivative D.
Definition
Given f ∈W n,p(Ω) and a cube Q, we call PnQ f to the polynomial ofdegree smaller than n restricted to Ω such that for any multiindex β with|β| < n,
3Q
DβPnQ f =
3Q
Dβf .
![Page 33: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/33.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
A necessity arises: approximating polynomials
We will use the Poincare inequality, that is, given f ∈W 1,p(Q),1 ≤ p ≤ ∞,
‖f −mQ f ‖Lp(Q) . `(Q)‖∇f ‖Lp(Q).
Equivalently, for any Sobolev function f with 0 mean on Q,
‖f ‖Lp(Q) . `(Q)‖∇f ‖Lp(Q).
If we want to apply recursively the Poincare inequality we need Df tohave mean 0 in 3Q for any partial derivative D.
Definition
Given f ∈W n,p(Ω) and a cube Q, we call PnQ f to the polynomial ofdegree smaller than n restricted to Ω such that for any multiindex β with|β| < n,
3Q
DβPnQ f =
3Q
Dβf .
![Page 34: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/34.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Properties of approximating polynomials
P1.∥∥f − PnQ f ∥∥Lp(3Q)
. `(Q)n‖∇nf ‖Lp(3Q).
P2. Given two neighbor Whitney cubes Q1 and Q2,∥∥PnQ1f − PnQ2
f∥∥L∞(3Q1∩3Q2)
. `(Q1)n−2p ‖∇nf ‖Lp(3Q1∪3Q2).
...
P5. We can bound the coefficients of the polynomialPnQ f (w) =
∑|γ|<n mQ,γ(w − xQ)γ :
|mQ,γ | .∑n−1
j=|γ|∥∥∇j f
∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 35: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/35.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Properties of approximating polynomials
P1.∥∥f − PnQ f ∥∥Lp(3Q)
. `(Q)n‖∇nf ‖Lp(3Q).
P2. Given two neighbor Whitney cubes Q1 and Q2,∥∥PnQ1f − PnQ2
f∥∥L∞(3Q1∩3Q2)
. `(Q1)n−2p ‖∇nf ‖Lp(3Q1∪3Q2).
...
P5. We can bound the coefficients of the polynomialPnQ f (w) =
∑|γ|<n mQ,γ(w − xQ)γ :
|mQ,γ | .∑n−1
j=|γ|∥∥∇j f
∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 36: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/36.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Properties of approximating polynomials
P1.∥∥f − PnQ f ∥∥Lp(3Q)
. `(Q)n‖∇nf ‖Lp(3Q).
P2. Given two neighbor Whitney cubes Q1 and Q2,∥∥PnQ1f − PnQ2
f∥∥L∞(3Q1∩3Q2)
. `(Q1)n−2p ‖∇nf ‖Lp(3Q1∪3Q2).
...
P5. We can bound the coefficients of the polynomialPnQ f (w) =
∑|γ|<n mQ,γ(w − xQ)γ :
|mQ,γ | .∑n−1
j=|γ|∥∥∇j f
∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 37: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/37.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Properties of approximating polynomials
P1.∥∥f − PnQ f ∥∥Lp(3Q)
. `(Q)n‖∇nf ‖Lp(3Q).
P2. Given two neighbor Whitney cubes Q1 and Q2,∥∥PnQ1f − PnQ2
f∥∥L∞(3Q1∩3Q2)
. `(Q1)n−2p ‖∇nf ‖Lp(3Q1∪3Q2).
...
P5. We can bound the coefficients of the polynomialPnQ f (w) =
∑|γ|<n mQ,γ(w − xQ)γ :
|mQ,γ | .∑n−1
j=|γ|∥∥∇j f
∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 38: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/38.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The proof: BP ∈ W n,p(Ω)⇒ ‖Bf ‖pW n,p(Ω) . ‖f ‖pW n,p(Ω)
Assume that, we have a bound for the polynomials. Fix a point x0 ∈ Ωand call Pλ(z) = (z − x0)λχΩ(z).
Given a cube Q, we can write
, using Newton’s binomial
PnQ f (w) = χΩ(w)∑|γ|<n
mQ,γ(w − xQ)γ
= χΩ(w)∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(w − x0)λ(x0 − xQ)γ−λ
so
DαB(PnQ f )(z) =∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(x0 − xQ)γ−λDα(BPλ)(z)
where, by P5,
|mQ,γ | .n−1∑j=|γ|
∥∥∇j f∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 39: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/39.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The proof: BP ∈ W n,p(Ω)⇒ ‖Bf ‖pW n,p(Ω) . ‖f ‖pW n,p(Ω)
Assume that, we have a bound for the polynomials. Fix a point x0 ∈ Ωand call Pλ(z) = (z − x0)λχΩ(z).Given a cube Q, we can write
, using Newton’s binomial
PnQ f (w) = χΩ(w)∑|γ|<n
mQ,γ(w − xQ)γ
= χΩ(w)∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(w − x0)λ(x0 − xQ)γ−λ
so
DαB(PnQ f )(z) =∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(x0 − xQ)γ−λDα(BPλ)(z)
where, by P5,
|mQ,γ | .n−1∑j=|γ|
∥∥∇j f∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 40: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/40.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The proof: BP ∈ W n,p(Ω)⇒ ‖Bf ‖pW n,p(Ω) . ‖f ‖pW n,p(Ω)
Assume that, we have a bound for the polynomials. Fix a point x0 ∈ Ωand call Pλ(z) = (z − x0)λχΩ(z).Given a cube Q, we can write, using Newton’s binomial
PnQ f (w) = χΩ(w)∑|γ|<n
mQ,γ(w − xQ)γ
= χΩ(w)∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(w − x0)λ(x0 − xQ)γ−λ
so
DαB(PnQ f )(z) =∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(x0 − xQ)γ−λDα(BPλ)(z)
where, by P5,
|mQ,γ | .n−1∑j=|γ|
∥∥∇j f∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 41: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/41.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The proof: BP ∈ W n,p(Ω)⇒ ‖Bf ‖pW n,p(Ω) . ‖f ‖pW n,p(Ω)
Assume that, we have a bound for the polynomials. Fix a point x0 ∈ Ωand call Pλ(z) = (z − x0)λχΩ(z).Given a cube Q, we can write, using Newton’s binomial
PnQ f (w) = χΩ(w)∑|γ|<n
mQ,γ(w − xQ)γ
= χΩ(w)∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(w − x0)λ(x0 − xQ)γ−λ
so
DαB(PnQ f )(z) =∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(x0 − xQ)γ−λDα(BPλ)(z)
where, by P5,
|mQ,γ | .n−1∑j=|γ|
∥∥∇j f∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 42: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/42.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The proof: BP ∈ W n,p(Ω)⇒ ‖Bf ‖pW n,p(Ω) . ‖f ‖pW n,p(Ω)
Assume that, we have a bound for the polynomials. Fix a point x0 ∈ Ωand call Pλ(z) = (z − x0)λχΩ(z).Given a cube Q, we can write, using Newton’s binomial
PnQ f (w) = χΩ(w)∑|γ|<n
mQ,γ(w − xQ)γ
= χΩ(w)∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(w − x0)λ(x0 − xQ)γ−λ
so
DαB(PnQ f )(z) =∑|γ|<n
mQ,γ
∑(0,0)≤λ≤γ
(γ
λ
)(x0 − xQ)γ−λDα(BPλ)(z)
where, by P5,
|mQ,γ | .n−1∑j=|γ|
∥∥∇j f∥∥L∞(3Q)
`(Q)j−|γ|.
![Page 43: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/43.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The Sobolev Embedding Theorem appears
Thus∥∥DαB(PnQ f )∥∥pLp(Q)
.∑j<n
∥∥∇j f∥∥pL∞
∑|γ|≤j
0≤λ≤γ
‖DαBPλ‖pLp(Q)H1(∂Ω)(j−|λ|)p.
Adding with respect to Q ∈ W, by the Sobolev Embedding Theorem(∥∥∇j f
∥∥L∞(Q∩Ω)
≤ C∥∥∇j f
∥∥W 1,p(Q∩Ω)
when p > 2), we get∑Q∈W
∥∥DαB(PnQ f )∥∥pLp(Q)
.∑j<n
∥∥∇j f∥∥pW 1,p(Q∩Ω)
∑0≤λ≤γ
‖BPλ‖pW n,p(Ω)
. ‖f ‖pW n,p(Q∩Ω).
![Page 44: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/44.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
The Sobolev Embedding Theorem appears
Thus∥∥DαB(PnQ f )∥∥pLp(Q)
.∑j<n
∥∥∇j f∥∥pL∞
∑|γ|≤j
0≤λ≤γ
‖DαBPλ‖pLp(Q)H1(∂Ω)(j−|λ|)p.
Adding with respect to Q ∈ W, by the Sobolev Embedding Theorem(∥∥∇j f
∥∥L∞(Q∩Ω)
≤ C∥∥∇j f
∥∥W 1,p(Q∩Ω)
when p > 2), we get∑Q∈W
∥∥DαB(PnQ f )∥∥pLp(Q)
.∑j<n
∥∥∇j f∥∥pW 1,p(Q∩Ω)
∑0≤λ≤γ
‖BPλ‖pW n,p(Ω)
. ‖f ‖pW n,p(Q∩Ω).
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Key Lemma: sticking to the essential
Lemma
Let Ω be a Lipschitz domain, Q a window, ψ ∈ C∞( 99100Q) with∥∥∇jψ
∥∥L∞
. 1R j for j ≥ 0. Then, for any |α| = n and f = ψ · f with
f ∈W n,p(Ω), TFAE:
‖DαBf ‖pLp(Q) . ‖f ‖pW n,p(Q∩Ω).∑
Q∈W∥∥DαB(PnQ f )
∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω).
Idea of the proof: separate local and non-local parts of the error term,
DαBf (z)− DαB(PnQ f )(z)
= DαB(χ2Q(f − PnQ f ))(z) + DαB((1− χ2Q)(f − PnQ f ))(z).
Sketch of the proof
![Page 46: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/46.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Key Lemma: sticking to the essential
Lemma
Let Ω be a Lipschitz domain, Q a window, ψ ∈ C∞( 99100Q) with∥∥∇jψ
∥∥L∞
. 1R j for j ≥ 0. Then, for any |α| = n and f = ψ · f with
f ∈W n,p(Ω), TFAE:
‖DαBf ‖pLp(Q) . ‖f ‖pW n,p(Q∩Ω).∑
Q∈W∥∥DαB(PnQ f )
∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω).
Idea of the proof: separate local and non-local parts of the error term,
DαBf (z)− DαB(PnQ f )(z)
= DαB(χ2Q(f − PnQ f ))(z) + DαB((1− χ2Q)(f − PnQ f ))(z).
Sketch of the proof
![Page 47: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/47.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
A geometric condition for the Beurling transform
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Theorem (Geometric condition on the boundary)
Let Ω be smooth enough. Then we can write
‖∂nBχΩ‖pLp(Ω) . ‖N‖p
Bn−1/pp,p (∂Ω)
+H1(∂Ω)2−np.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Theorem (Geometric condition on the boundary)
Let Ω be smooth enough. Then we can write
‖∂nBχΩ‖pLp(Ω) . ‖N‖p
Bn−1/pp,p (∂Ω)
+H1(∂Ω)2−np.
![Page 50: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/50.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Defining some generalized betas of David-Semmes
A measure of the flatness of a set Γ:
Definition (P. Jones)
βΓ(Q) = infVw(V )`(Q)
If there is no risk of confusion,we will write just β(n)(I ).
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Defining some generalized betas of David-Semmes
A measure of the flatness of a set Γ:
Definition (P. Jones)
βΓ(Q) = infVw(V )`(Q)
If there is no risk of confusion,we will write just β(n)(I ).
![Page 52: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/52.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Defining some generalized betas of David-Semmes
The graph of a function y = A(x):Consider I ⊂ R, and define
Definition
β∞(I ,A) = infP∈P1
∥∥∥A−P`(I )
∥∥∥∞
If there is no risk of confusion,we will write just β(n)(I ).
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Defining some generalized betas of David-Semmes
The graph of a function y = A(x):Consider I ⊂ R, and define
Definition
β∞(I ,A) = infP∈P1
∥∥∥A−P`(I )
∥∥∥∞
If there is no risk of confusion,we will write just β(n)(I ).
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Defining some generalized betas of David-Semmes
The graph of a function y = A(x):Consider I ⊂ R, and define
Definition
βp(I ,A) = infP∈P11
`(I )1p
∥∥∥A−P`(I )
∥∥∥p
If there is no risk of confusion,we will write just β(n)(I ).
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Defining some generalized betas of David-Semmes
The graph of a function y = A(x):Consider I ⊂ R, and define
Definition
β(n)(I ,A) = infP∈Pn1`(I )
∥∥∥A−P`(I )
∥∥∥1
If there is no risk of confusion,we will write just β(n)(I ).
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Relation between β(n) and Bnp,p
Theorem (Dorronsoro)
Let f : R→ R be a function in the homogeneous Besov space Bsp,p.
Then, for any n ≥ [s],
‖f ‖pBsp,p
≈∑I∈D
(β(n)(I )
`(I )s−1
)p
`(I ).
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Whitney decomposition
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Whitney decomposition
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Whitney decomposition
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Bounds for the first derivative
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Bounds for the first derivative
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Bounds for the first derivative
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Second order derivative
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Second order derivative
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Higher order derivatives
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Local charts: Higher order derivatives
First order derivative Second order derivative Higher order derivatives Skip higher order derivatives
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Bounding the polynomial region
We can choose the window length R small enough so that
Proposition
If we denote by ΩQ the region with boundary a minimizing polynomial forβ(n)(Φ(Q)), we get ∣∣∂nBχΩQ
∣∣ ≤ C
Rn.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Bounding the polynomial region
We can choose the window length R small enough so that
Proposition
If we denote by ΩQ the region with boundary a minimizing polynomial forβ(n)(Φ(Q)), we get ∣∣∂nBχΩQ
∣∣ ≤ C
Rn.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Bounding the interstitial region
Proposition
Choosing a minimizing polynomial for β(n)(Φ(Q)), we get
ˆΩ∆ΩQ
dm(w)
|z − w |n+2.
∑I∈D
Φ(Q)⊂I⊂Φ(Qk )
β(n)(I )
`(I )n+
1
Rn.
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Holder inequalities do the rest
Theorem
Let Ω be a Lipschitz domain of order n. Then, with the previous notation,
‖∂nBχΩ‖pLp(Ω) .N∑
k=1
∑I∈Dk
(β(n)(I )
`(I )n−1/p
)p
`(I ) +H1(∂Ω)2−np.
Back
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Holder inequalities do the rest
Theorem
Let Ω be a Lipschitz domain of order n. Then, with the previous notation,
‖∂nBχΩ‖pLp(Ω) .N∑
k=1
‖Ak‖pB
n−1/p+1p,p
+H1(∂Ω)2−np.
Back
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Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Holder inequalities do the rest
Using a decomposition in windows,
Theorem
Let Ω be a Lipschitz domain of order n. Then, with the previous notation,
‖∂nBχΩ‖pLp(Ω) . ‖N‖p
Bn−1/pp,p (∂Ω)
+H1(∂Ω)2−np.
Back
![Page 73: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/73.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Conclusions
For p > 2 we have a T (P) theoremfor any Calderon-Zygmund operator of convolution typein any ambient space as long as we have uniform boundsin the derivatives of its kernel.
In the complex plane, the Besov regularity Bn−1/pp,p
of the normal vector to the boundary of the domaingives us a bound of B(P) in W n,p (and 0 < s < 1).
Next steps:
Proving analogous results for any s ∈ R+.Looking for a more general set of operators wherethe Besov condition on the boundary implies Sobolev boundedness.Giving a necessary condition for the boundednessof the Beurling transform when p ≤ 2.Sharpness of all those results.
![Page 74: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/74.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Conclusions
For p > 2 we have a T (P) theoremfor any Calderon-Zygmund operator of convolution typein any ambient space as long as we have uniform boundsin the derivatives of its kernel.
In the complex plane, the Besov regularity Bn−1/pp,p
of the normal vector to the boundary of the domaingives us a bound of B(P) in W n,p (and 0 < s < 1).
Next steps:
Proving analogous results for any s ∈ R+.Looking for a more general set of operators wherethe Besov condition on the boundary implies Sobolev boundedness.Giving a necessary condition for the boundednessof the Beurling transform when p ≤ 2.Sharpness of all those results.
![Page 75: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/75.jpg)
Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform
Conclusions
For p > 2 we have a T (P) theoremfor any Calderon-Zygmund operator of convolution typein any ambient space as long as we have uniform boundsin the derivatives of its kernel.
In the complex plane, the Besov regularity Bn−1/pp,p
of the normal vector to the boundary of the domaingives us a bound of B(P) in W n,p (and 0 < s < 1).
Next steps:
Proving analogous results for any s ∈ R+.Looking for a more general set of operators wherethe Besov condition on the boundary implies Sobolev boundedness.Giving a necessary condition for the boundednessof the Beurling transform when p ≤ 2.Sharpness of all those results.
![Page 76: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/76.jpg)
Farewell
Thank you!
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∅
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Key Lemma: sticking to the essential
Lemma
Let Ω be a Lipschitz domain, Q a window, ψ ∈ C∞( 99100Q) with∥∥∇jψ
∥∥L∞
. 1R j for j ≥ 0. Then, for any |α| = n and f = ψ · f with
f ∈W n,p(Ω), TFAE:
‖DαBf ‖pLp(Q) . ‖f ‖pW n,p(Q∩Ω).∑
Q∈W∥∥DαB(PnQ f )
∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω).
We will see that∥∥∥∥∥DαBf −∑Q∈W
χQDαB(PnQ f )
∥∥∥∥∥p
Lp(Q)
. ‖f ‖pW n,p(Q∩Ω).
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Key Lemma: sticking to the essential
Lemma
Let Ω be a Lipschitz domain, Q a window, ψ ∈ C∞( 99100Q) with∥∥∇jψ
∥∥L∞
. 1R j for j ≥ 0. Then, for any |α| = n and f = ψ · f with
f ∈W n,p(Ω), TFAE:
‖DαBf ‖pLp(Q) . ‖f ‖pW n,p(Q∩Ω).∑
Q∈W∥∥DαB(PnQ f )
∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω).
We will see that∥∥∥∥∥DαBf −∑Q∈W
χQDαB(PnQ f )
∥∥∥∥∥p
Lp(Q)
. ‖f ‖pW n,p(Q∩Ω).
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Breaking the integral into local and non-local parts
Take χ 32 Q≤ ϕQ ≤ χ2Q a smooth bump function.
For z ∈ Q,
DαBf (z)− DαB(PnQ f )(z)
= DαB(ϕQ(f − PnQ f ))(z) + DαB((χΩ − ϕQ)(f − PnQ f ))(z).
Thus, we need to prove that the local part is bounded
1 =∑Q∈W
∥∥DαB(ϕQ(f − PnQ f ))∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω)
and the non-local part is bounded
2 =∑Q∈W
∥∥DαB((χΩ − ϕQ)(f − PnQ f ))∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω)
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Breaking the integral into local and non-local parts
Take χ 32 Q≤ ϕQ ≤ χ2Q a smooth bump function. For z ∈ Q,
DαBf (z)− DαB(PnQ f )(z)
= DαB(ϕQ(f − PnQ f ))(z) + DαB((χΩ − ϕQ)(f − PnQ f ))(z).
Thus, we need to prove that the local part is bounded
1 =∑Q∈W
∥∥DαB(ϕQ(f − PnQ f ))∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω)
and the non-local part is bounded
2 =∑Q∈W
∥∥DαB((χΩ − ϕQ)(f − PnQ f ))∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω)
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Breaking the integral into local and non-local parts
Take χ 32 Q≤ ϕQ ≤ χ2Q a smooth bump function. For z ∈ Q,
DαBf (z)− DαB(PnQ f )(z)
= DαB(ϕQ(f − PnQ f ))(z) + DαB((χΩ − ϕQ)(f − PnQ f ))(z).
Thus, we need to prove that the local part is bounded
1 =∑Q∈W
∥∥DαB(ϕQ(f − PnQ f ))∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω)
and the non-local part is bounded
2 =∑Q∈W
∥∥DαB((χΩ − ϕQ)(f − PnQ f ))∥∥pLp(Q)
. ‖f ‖pW n,p(Q∩Ω)
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The local part 1 =∑
Q∈W∥∥DαB(ϕQ(f − Pn
Qf ))∥∥pLp(Q)
As ϕQ(f − PnQ f ) ∈W n,p(C), the Beurling transform commutes with thederivative∥∥DαB(ϕQ(f − PnQ f ))
∥∥pLp(Q)
=∥∥BDα(ϕQ(f − PnQ f ))
∥∥pLp(Q)
Using P1 and P4, we get∥∥DαB(ϕQ(f − PnQ f ))∥∥pLp(Q)
. ‖∇nf ‖pLp(3Q).
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The local part 1 =∑
Q∈W∥∥DαB(ϕQ(f − Pn
Qf ))∥∥pLp(Q)
As ϕQ(f − PnQ f ) ∈W n,p(C), the Beurling transform commutes with thederivative∥∥DαB(ϕQ(f − PnQ f ))
∥∥pLp(Q)
. ‖B‖pp∥∥Dα(ϕQ(f − PnQ f ))
∥∥pLp(C)
Using P1 and P4, we get∥∥DαB(ϕQ(f − PnQ f ))∥∥pLp(Q)
. ‖∇nf ‖pLp(3Q).
![Page 85: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/85.jpg)
The local part 1 =∑
Q∈W∥∥DαB(ϕQ(f − Pn
Qf ))∥∥pLp(Q)
As ϕQ(f − PnQ f ) ∈W n,p(C), the Beurling transform commutes with thederivative∥∥DαB(ϕQ(f − PnQ f ))
∥∥pLp(Q)
. ‖B‖pp∥∥Dα(ϕQ(f − PnQ f ))
∥∥pLp(C)
Using P1 and P4, we get∥∥DαB(ϕQ(f − PnQ f ))∥∥pLp(Q)
. ‖∇nf ‖pLp(3Q).
![Page 86: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/86.jpg)
Breaking the non-local part2 =
∑Q∈W
∥∥DαB((χΩ − ϕQ)(f − PnQf ))
∥∥pLp(Q)
In the non-local part we can take the derivative in the kernel of thetransform (let’s call it B(−α))
and use a partition of unityχΩ − ϕQ =
∑S∈W ψQS related to the covering 2SS∈W with the usual
bounds in their derivatives.Then,
2 ≤∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(f − PnS f ))∥∥∥Lp(Q)
)p
+∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(PnS f − PnQ f ))
∥∥∥Lp(Q)
)p
= 3 + 4 .
![Page 87: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/87.jpg)
Breaking the non-local part2 =
∑Q∈W
∥∥DαB((χΩ − ϕQ)(f − PnQf ))
∥∥pLp(Q)
In the non-local part we can take the derivative in the kernel of thetransform (let’s call it B(−α)) and use a partition of unityχΩ − ϕQ =
∑S∈W ψQS related to the covering 2SS∈W with the usual
bounds in their derivatives.
Then,
2 ≤∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(f − PnS f ))∥∥∥Lp(Q)
)p
+∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(PnS f − PnQ f ))
∥∥∥Lp(Q)
)p
= 3 + 4 .
![Page 88: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/88.jpg)
Breaking the non-local part2 =
∑Q∈W
∥∥DαB((χΩ − ϕQ)(f − PnQf ))
∥∥pLp(Q)
In the non-local part we can take the derivative in the kernel of thetransform (let’s call it B(−α)) and use a partition of unityχΩ − ϕQ =
∑S∈W ψQS related to the covering 2SS∈W with the usual
bounds in their derivatives.Then,
2 ≤∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(f − PnS f ))∥∥∥Lp(Q)
)p
+∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(PnS f − PnQ f ))
∥∥∥Lp(Q)
)p
= 3 + 4 .
![Page 89: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/89.jpg)
The non-local part re-localized 3
The re-localized sum is the easier to bound. Using the Holder inequalityand the Poincare inequality, we get
|B(−α)(ψQS(f − PnS f ))(z)| . `(S)n+ 2
p′
D(Q,S)n+2‖∇nf ‖Lp(3S).
Using this uniform bound on Q, the properties of the covering and someHolder inequalities, we bound
3 . ‖∇nf ‖pLp(Q).
Proof
![Page 90: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/90.jpg)
The non-local part re-localized 3
The re-localized sum is the easier to bound. Using the Holder inequalityand the Poincare inequality, we get
|B(−α)(ψQS(f − PnS f ))(z)| . `(S)n+ 2
p′
D(Q,S)n+2‖∇nf ‖Lp(3S).
Using this uniform bound on Q, the properties of the covering and someHolder inequalities, we bound
3 . ‖∇nf ‖pLp(Q).
Proof
![Page 91: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/91.jpg)
Internal structure of the cubes family
Q
R
δh(Q,R)
We can define the longdistance
D(Q,R) =δh(Q,R) + `(Q) + `(R).
We find a natural way todefine fathers and sons inthe Whitney family.
Given two cubes Q and R wecan look for a commonancestor, but it is better tolook for neighbor ancestors,QR and RQ :D(Q,R) ≈ `(QR) ≈ `(RQ).
![Page 92: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/92.jpg)
Internal structure of the cubes family
Q
R
D(Q,R)
We can define the longdistanceD(Q,R) =δh(Q,R) + `(Q) + `(R).
We find a natural way todefine fathers and sons inthe Whitney family.
Given two cubes Q and R wecan look for a commonancestor, but it is better tolook for neighbor ancestors,QR and RQ :D(Q,R) ≈ `(QR) ≈ `(RQ).
![Page 93: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/93.jpg)
Internal structure of the cubes family
Q
R
D(Q,R)
We can define the longdistanceD(Q,R) =δh(Q,R) + `(Q) + `(R).
We find a natural way todefine fathers and sons inthe Whitney family.
Given two cubes Q and R wecan look for a commonancestor, but it is better tolook for neighbor ancestors,QR and RQ :D(Q,R) ≈ `(QR) ≈ `(RQ).
![Page 94: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/94.jpg)
Internal structure of the cubes family
Q
R
D(Q,R)
We can define the longdistanceD(Q,R) =δh(Q,R) + `(Q) + `(R).
We find a natural way todefine fathers and sons inthe Whitney family.
Given two cubes Q and R wecan look for a commonancestor,
but it is better tolook for neighbor ancestors,QR and RQ :D(Q,R) ≈ `(QR) ≈ `(RQ).
![Page 95: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/95.jpg)
Internal structure of the cubes family
Q
R
QR RQ
D(Q,R)
We can define the longdistanceD(Q,R) =δh(Q,R) + `(Q) + `(R).
We find a natural way todefine fathers and sons inthe Whitney family.
Given two cubes Q and R wecan look for a commonancestor, but it is better tolook for neighbor ancestors,QR and RQ :
D(Q,R) ≈ `(QR) ≈ `(RQ).
![Page 96: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/96.jpg)
Internal structure of the cubes family
Q
R
QR RQ
D(Q,R)
We can define the longdistanceD(Q,R) =δh(Q,R) + `(Q) + `(R).
We find a natural way todefine fathers and sons inthe Whitney family.
Given two cubes Q and R wecan look for a commonancestor, but it is better tolook for neighbor ancestors,QR and RQ :D(Q,R) ≈ `(QR) ≈ `(RQ).
![Page 97: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/97.jpg)
Sketch of the boundedness of the non-local part 4
QS
The difference between polynomials ofdistant cubes can be huge.
We take a tour changing betweenneighbor cubes.
We apply the property P3 to onebranch to illustrate.
|B(−α)[(PnS f − P
nQ f )ψQS
](z)|
.ˆ
2S
|PnS f (w)− PnQ f (w)|D(Q,S)n+2
dm(w)
.1
D(Q,S)n+2
ˆ2S
∑Q≤P<S
|PnP f (w)− PnN (P)f (w)|dm(w)
.∑
Q≤P<S
`(S)2 D(P,S)n−1
D(Q,S)n+2`(P)1− 2
p ‖∇nf ‖Lp(5P)
![Page 98: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/98.jpg)
Sketch of the boundedness of the non-local part 4
QS
The difference between polynomials ofdistant cubes can be huge.
We take a tour changing betweenneighbor cubes.
We apply the property P3 to onebranch to illustrate.
|B(−α)[(PnS f − P
nQ f )ψQS
](z)| .
ˆ2S
|PnS f (w)− PnQ f (w)|D(Q,S)n+2
dm(w)
.1
D(Q,S)n+2
ˆ2S
∑Q≤P<S
|PnP f (w)− PnN (P)f (w)|dm(w)
.∑
Q≤P<S
`(S)2 D(P,S)n−1
D(Q,S)n+2`(P)1− 2
p ‖∇nf ‖Lp(5P)
![Page 99: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/99.jpg)
Sketch of the boundedness of the non-local part 4
QS
QS SQThe difference between polynomials ofdistant cubes can be huge.
We take a tour changing betweenneighbor cubes.
We apply the property P3 to onebranch to illustrate.
|B(−α)[(PnS f − P
nQ f )ψQS
](z)| .
ˆ2S
|PnS f (w)− PnQ f (w)|D(Q,S)n+2
dm(w)
.1
D(Q,S)n+2
ˆ2S
∑Q≤P<S
|PnP f (w)− PnN (P)f (w)|dm(w)
.∑
Q≤P<S
`(S)2 D(P,S)n−1
D(Q,S)n+2`(P)1− 2
p ‖∇nf ‖Lp(5P)
![Page 100: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/100.jpg)
Sketch of the boundedness of the non-local part 4
QS
SQThe difference between polynomials ofdistant cubes can be huge.
We take a tour changing betweenneighbor cubes.
We apply the property P3 to onebranch to illustrate.
|B(−α)[(PnS f − P
nSQf )ψQS
](z)| .
ˆ2S
|PnS f (w)− PnSQf (w)|
D(Q,S)n+2dm(w)
.1
D(Q,S)n+2
ˆ2S
∑S<P≤SQ
|PnP f (w)− PnN (P)f (w)|dm(w)
.∑
S<P≤SQ
`(S)2 D(P,S)n−1
D(Q,S)n+2`(P)1− 2
p ‖∇nf ‖Lp(5P)
![Page 101: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/101.jpg)
Sketch of the boundedness of the non-local part 4
QS
SQ
The difference between polynomials ofdistant cubes can be huge.
We take a tour changing betweenneighbor cubes.
We apply the property P3 to onebranch to illustrate.
Holder inequalities and the propeties ofthe Whitney covering will do the rest.
Details
4* .∑P∈W
‖∇nf ‖pLp(5P)`(P)p−52
∑Q∈W
`(Q)32
D(Q,P)2p− 12
∑S<P
`(S)p+ 12
. ‖∇nf ‖pLp(Q∩Ω).
Back
![Page 102: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/102.jpg)
Bounding 3
The uniform bound in every square leads to
3 .∑Q∈W
(∑S∈W
`(Q)2p `(S)
n+ 2p′
D(Q,S)n+2‖∇nf ‖Lp(3S)
)p
and, applying the Holder inequality,
3 .∑Q∈W
∑S∈W
`(Q)2`(S)np
D(Q,S)32 +np‖∇nf ‖pLp(3S)
(∑S∈W
`(S)2
D(Q,S)2+ p′2p
) pp′
Lemma
Let b > a > 1. Then,∑R∈W
`(R)a
D(Q,R)b≤ Ca,b`(Q)a−b.
![Page 103: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/103.jpg)
Bounding 3
The uniform bound in every square leads to
3 .∑Q∈W
(∑S∈W
`(Q)2p `(S)
n+ 2p′
D(Q,S)n+2‖∇nf ‖Lp(3S)
)p
and, applying the Holder inequality,
3 .∑Q∈W
∑S∈W
`(Q)2`(S)np
D(Q,S)32 +np‖∇nf ‖pLp(3S)
(∑S∈W
`(S)2
D(Q,S)2+ p′2p
) pp′
Lemma
Let b > a > 1. Then,∑R∈W
`(R)a
D(Q,R)b≤ Ca,b`(Q)a−b.
![Page 104: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/104.jpg)
Bounding 3
3 ≤ Cp
∑S∈W
`(S)np‖∇nf ‖pLp(3S)
∑Q∈W
`(Q)2
D(Q,S)32 +np
`(Q)−12
As 32 + np > 3
2 > 1, we can use the previous lemma again to get
3 ≤ Cn,p
∑S∈W
`(S)np‖∇nf ‖pLp(3S)`(S)−np
. ‖∇nf ‖pLp(Q∩Ω)
Back
![Page 105: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/105.jpg)
Bounding 4
We have
4∗QS = |B(−α)[(PnS f − P
nSQf )ψQS
](z)|
.∑
S<P≤SQ
`(S)2 D(P,S)n−1
D(Q,S)n+2`(P)1− 2
p ‖∇nf ‖Lp(5P).
On the other hand, as S < P ≤ SQ , we have
D(P,S) ≈ `(P) ≤ `(SQ) ≈ D(Q,S)
andD(Q,S) ≈ `(SQ) = `(PQ) ≈ D(Q,P).
Thus,
4∗Q ≤ C
∑S∈W
∑S<P≤SQ
`(S)2`(P)1− 2p ‖∇nf ‖Lp(5P)
D(Q,P)3
p
.
![Page 106: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/106.jpg)
Bounding 4
We have
4∗QS = |B(−α)[(PnS f − P
nSQf )ψQS
](z)|
.∑
S<P≤SQ
`(S)2 D(P,S)n−1
D(Q,S)n+2`(P)1− 2
p ‖∇nf ‖Lp(5P).
On the other hand, as S < P ≤ SQ , we have
D(P,S) ≈ `(P) ≤ `(SQ) ≈ D(Q,S)
andD(Q,S) ≈ `(SQ) = `(PQ) ≈ D(Q,P).
Using Holder inequality, we get
4∗Q .
∑S
(∑P
`(S)2p`(P)p−52 ‖∇nf ‖pLp(5P)
D(Q,P)3p
) 1p(∑
P
`(P)p′2p
) 1p′p
.
![Page 107: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/107.jpg)
Bounding 4
4∗QS = |B(−α)[(PnS f − P
nSQf )ψQS
](z)|.
The sum∑
S<P≤SQ`(P)
p′2p is geometric. Thus ∑
S<P≤SQ
`(P)p′2p
1p′
. `(SQ)1
2p ≈ `(S)1
2p−1
D(Q,P)−1
2p−1
`(S)1− 12p
D(Q,S)
Then,
4∗Q .
∑S
(∑P
`(S)2p`(P)p−52 ‖∇nf ‖pLp(5P)
D(Q,P)3p
) 1p(∑
P
`(P)p′2p
) 1p′p
.
∑S
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52 ‖∇nf ‖pLp(5P)
D(Q,P)2p− 12
1p
`(S)1− 12p
D(Q,S)
p
![Page 108: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/108.jpg)
Bounding 4
4∗QS = |B(−α)[(PnS f − P
nSQf )ψQS
](z)|.
The sum∑
S<P≤SQ`(P)
p′2p is geometric. Thus ∑
S<P≤SQ
`(P)p′2p
1p′
. `(SQ)1
2p ≈ `(S)1
2p−1
D(Q,P)−1
2p−1
`(S)1− 12p
D(Q,S)
Then,
4∗Q .
∑S
(∑P
`(S)2p`(P)p−52 ‖∇nf ‖pLp(5P)
D(Q,P)3p
) 1p(∑
P
`(P)p′2p
) 1p′p
.
∑S
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52 ‖∇nf ‖pLp(5P)
D(Q,P)2p− 12
1p
`(S)1− 12p
D(Q,S)
p
![Page 109: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/109.jpg)
Bounding 4
4∗QS = |B(−α)[(PnS f − P
nSQf )ψQS
](z)|.
The sum∑
S<P≤SQ`(P)
p′2p is geometric. Thus ∑
S<P≤SQ
`(P)p′2p
1p′
. `(SQ)1
2p ≈ `(S)1
2p−1
D(Q,P)−1
2p−1
`(S)1− 12p
D(Q,S)
Then, we apply Holder inequality
4∗Q .
∑S
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52 ‖∇nf ‖pLp(5P)
D(Q,P)2p− 12
1p
`(S)1− 12p
D(Q,S)
p
.∑S
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52 ‖∇nf ‖pLp(5P)
D(Q,P)2p− 12
∑S
`(S)p′− p′
2p
D(Q,S)p′
pp′
![Page 110: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/110.jpg)
Bounding 4
4∗QS = |B(−α)[(PnS f − P
nSQf )ψQS
](z)|.
The sum∑
S<P≤SQ`(P)
p′2p is geometric. Thus ∑
S<P≤SQ
`(P)p′2p
1p′
. `(SQ)1
2p ≈ `(S)1
2p−1
D(Q,P)−1
2p−1
`(S)1− 12p
D(Q,S)
Then, we apply Holder inequality and the properties of the covering,
4∗Q .∑S
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52 ‖∇nf ‖pLp(5P)
D(Q,P)2p− 12
∑S
`(S)p′− p′
2p
D(Q,S)p′
pp′
.∑S∈W
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52
D(Q,P)2p− 12 `(Q)
12
‖∇nf ‖pLp(5P).
![Page 111: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/111.jpg)
Bounding 4
4∗QS = |B(−α)[(PnS f − P
nSQf )ψQS
](z)|.
Then,
4∗Q .∑S∈W
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52
D(Q,P)2p− 12 `(Q)
12
‖∇nf ‖pLp(5P).
Summing with respect to Q, we have
4* .∑Q∈W
`(Q)2∑S∈W
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52
D(Q,P)2p− 12 `(Q)
12
‖∇nf ‖pLp(5P)
≤∑P∈W
‖∇nf ‖pLp(5P)`(P)p−52
∑Q∈W
`(Q)32
D(Q,P)2p− 12
∑S<P
`(S)p+ 12 .
![Page 112: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/112.jpg)
Bounding 4
4* =∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(PnS f − PnSQf ))∥∥∥Lp(Q)
)p
Then,
4∗Q .∑S∈W
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52
D(Q,P)2p− 12 `(Q)
12
‖∇nf ‖pLp(5P).
Summing with respect to Q, we have
4* .∑Q∈W
`(Q)2∑S∈W
∑S<P≤SQ
`(S)p+ 12 `(P)p−
52
D(Q,P)2p− 12 `(Q)
12
‖∇nf ‖pLp(5P)
≤∑P∈W
‖∇nf ‖pLp(5P)`(P)p−52
∑Q∈W
`(Q)32
D(Q,P)2p− 12
∑S<P
`(S)p+ 12 .
![Page 113: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/113.jpg)
Bounding 4
4* =∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(PnS f − PnSQf ))∥∥∥Lp(Q)
)p
We have found out
4* .∑P∈W
‖∇nf ‖pLp(5P)`(P)p−52
∑Q∈W
`(Q)32
D(Q,P)2p− 12
∑S<P
`(S)p+ 12 .
Now, being p + 12 > 1 and 2p − 1
2 >32 > 1 imply
∑`(S)p+ 1
2 . `(P)p+ 12 and
∑ `(Q)32
D(Q,P)2p− 12
. `(P)−2(p−1)
so
4* .∑P∈W
`(P)p−52−2p+2+p+ 1
2 ‖∇nf ‖pLp(5P) . ‖∇nf ‖pLp(Q∩Ω).
Back
![Page 114: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/114.jpg)
Bounding 4
4* =∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(PnS f − PnSQf ))∥∥∥Lp(Q)
)p
We have found out
4* .∑P∈W
‖∇nf ‖pLp(5P)`(P)p−52
∑Q∈W
`(Q)32
D(Q,P)2p− 12
∑S<P
`(S)p+ 12 .
Now, being p + 12 > 1 and 2p − 1
2 >32 > 1 imply
∑`(S)p+ 1
2 . `(P)p+ 12 and
∑ `(Q)32
D(Q,P)2p− 12
. `(P)−2(p−1)
so
4* .∑P∈W
`(P)p−52−2p+2+p+ 1
2 ‖∇nf ‖pLp(5P) . ‖∇nf ‖pLp(Q∩Ω).
Back
![Page 115: mat.uab.catmat.uab.cat/ges/wp-content/uploads/2013/12/prats-presentacio.pdf · Introduction Proof of the T(P) Theorem A geometric condition for the Beurling transform Known facts,](https://reader034.vdocuments.us/reader034/viewer/2022052016/602ea575e61b74704b141a0b/html5/thumbnails/115.jpg)
Bounding 4
4* =∑Q∈W
(∑S∈W
∥∥∥B(−α)(ψQS(PnS f − PnSQf ))∥∥∥Lp(Q)
)p
We have found out
4* .∑P∈W
‖∇nf ‖pLp(5P)`(P)p−52
∑Q∈W
`(Q)32
D(Q,P)2p− 12
∑S<P
`(S)p+ 12 .
Now, being p + 12 > 1 and 2p − 1
2 >32 > 1 imply
∑`(S)p+ 1
2 . `(P)p+ 12 and
∑ `(Q)32
D(Q,P)2p− 12
. `(P)−2(p−1)
so
4* .∑P∈W
`(P)p−52−2p+2+p+ 1
2 ‖∇nf ‖pLp(5P) . ‖∇nf ‖pLp(Q∩Ω).
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