algebraic collective model and its applications gabriela thiamov laboratoire de physique subatomique...
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Algebraic collective model and its applications
Gabriela Thiamová
Laboratoire de Physique Subatomique et de CosmologieInstitut National Polytechnique de Grenoble
France
Sofia, October 8-10, 2015
1
1) IBM-BM relationship in various dynamical symmetry limits -in the spherical vibrator U(5) limit -in the O(6) limit -in the rigid-rotor limit
2) The algebraic collective model (ACM)
3) IBM-BM relationship in the triaxial limit
4) ACM applications (single and multi-phonon excitations)
5) Conclusions
Outline of the presentation
2
IBM-BM relationship in various dynamical symmetry limits
In the spherical vibrator U(5) limit the IBM dynamical subgroup chain
contracts in the N ∞ limit to the BM dynamicalsymmetry chain
D. J. Rowe and G. Thiamova, NPA 760 (2005), 59
Heisenberg-Weyl algebrafor the BM spanned by qm,
m=0, ± 1, ± 2, I
Any developments in the U(5) limit of one modelapply equally to the other
IBM
BM
3
The O(6) basis :
-similarly to the U(5) limit, there is a close correspondence of the physicsof the IBM in its O(6) limit with the BM in its rigid-beta gamma-softWilets-Jean limit.
This correspondence is precise in the limit in which the IBM dynamicalsymmetry group contracts to the chain of the Wilets-Jean model
N ∞ contraction
IBM
BM
4
IBM-BM relationship in various dynamical symmetry limits
5
IBM-BM relationship in various dynamical symmetry limits
The O(6) basis :
-similarly to the U(5) limit, there is a close correspondence of the physicsof the IBM in its O(6) limit with the BM in its rigid-beta gamma-softWilets-Jean limit.
This correspondence is precise in the limit in which the IBM dynamicalsymmetry group contracts to the chain of the Wilets-Jean model
IBM
BM
N ∞ contraction
There is a problem with the BM subgroup chain !
-the delta-function nature of the WJ rigid-beta states-they do not have a convergent expansion in terms of the
U(5) states in the BM.
This problem is circumvented in the ACM model !6
IBM-BM relationship in various dynamical symmetry limits
The O(6) basis :
-similarly to the U(5) limit, there is a close correspondence of the physicsof the IBM in its O(6) limit with the BM in its rigid-beta gamma-softWilets-Jean limit.
This correspondence is precise in the limit in which the IBM dynamicalsymmetry group contracts to the chain of the Wilets-Jean model
IBM
BM
N ∞ contraction
There is a problem with the BM subgroup chain !
-the delta-function nature of the WJ rigid-beta states-they do not have a convergent expansion in terms of the
U(5) states in the BM.
Rigid rotor states
In the BM the beta and gamma rigid subgroup chain
is a submodel of the beta rigid subgroup chain
as much as is a subgroup of
w.f. are delta-func.in β and γ -
a problem !!!
7
IBM-BM relationship in various dynamical symmetry limits
Rigid rotor states
In the BM the beta and gamma rigid subgroup chain
is a submodel of the beta rigid subgroup chain
as much as is a subgroup of
In the IBM
is not a submodel ofbecause SU(3) is not a subgroup of O(6)
However
w.f. are delta-func.in β and γ -
a problem !!!
8
IBM-BM relationship in various dynamical symmetry limits
The rotor-like states of the of the SU(3) limit of the IBM are notrelated to those of its O(6) limit in ways that parallel the relationship
between the rigid-rotor and rigid-beta states in the BM. 9
IBM-BM relationship in various dynamical symmetry limits
Rigid rotor states
In the BM the beta and gamma rigid subgroup chain
is a submodel of the beta rigid subgroup chain
as much as is a subgroup of
In the IBM
is not a submodel ofbecause SU(3) is not a subgroup of O(6)
However
w.f. are delta-func.in β and γ -
a problem !!!
A dynamical subgroup chain is used in the ACM to define a continuous set of basis states for the BM :
dynamical groupfor radial (beta)wave functions
λ= v+5/2 – basis states are those of the harmonic spherical vibrator– convenient for spherical and near spherical nuclei
Deformed nuclei – much more rapid convergence for a suitably chosenmodified SU(1,1) representation – radial w. f. obtained by modifying theSO(5) centrifugal potential.
Davidson basis – λv = 1 + [(v+3/2)2 + β04]1/2
Angular part SO(5) spherical harmonicschar. by seniority v (ang. mom.)
10
Algebraic Collective Model (ACM)
)2()3()3(][)5(][)5()]5([ 55 SOSOSORSORUHW
The rigid rotor states of the BM subgroup chain
are approached with the Hamiltonians
3cosˆˆ H
.)(0
ˆˆˆˆˆ QQQH
in the ACM (beta rigid)
in the IBM
.~~ˆ dssdQ
O(6) quadrupole op.
the SO(5) Casimir inv.
mixes O(5) irreps but preserves O(6) and SO(3) quantum numbers
D. J. Rowe and G. Thiamova, Nucl. Phys. A 760, 59 (2005).
σ ∞ contraction
11
Algebraic Collective Model (ACM)
IBM-BM relationship in triaxial limit
ACM-IBM calculations in the beta-rigid limit
G. Thiamova, D. J. Rowe and M. A. Caprio Nucl. Phys. A 895, 20 (2012). 12
Generic triaxial case
G. Thiamova, D. J. Rowe and M. A. Caprio Nucl. Phys. A 895, 20 (2012). 13
IBM IBM
IBMACM
IBM-BM relationship in triaxial limit
Equlibrium γ = 30° case
A pure potential canonly be reachedin the limit
G. Thiamova, D. J. Rowe and M. A. Caprio Nucl. Phys. A 895, 20 (2012). 14
IBM IBM
IBMACM
IBM-BM relationship in triaxial limit
A more direct measure of thecloseness of the IBM andthe ACM results
The progression ofthe IBM effective γvalues to their ACMcounterparts
γeff non-zero even in theaxially-symmetric case !
G. Thiamova, D. J. Rowe and M. A. Caprio Nucl. Phys. A 895, 20 (2012). 15
IBM-BM relationship in triaxial limit
16
IBM-ACM beta-rigid calculations for N=10, 20 and 40
R1= Eγγ (K=0)/Eγ R2=Eγγ
(K=4)/Eγ
boson number
N 10 20 40 ACM
General triaxial R1 =2.82 R1 =3.40 R1 =3.29 R1 =3.54
R2=2.50 R2=3.09 R2=2.57 R2=2.62
G. Thiamova, D. J. Rowe and M. A. Caprio Nucl. Phys. A 895, 20 (2012).
IBM-BM relationship in triaxial limit
Applications (single and multi-phonon excitations)
17
Various model predictions for double-gamma states are controversial....
18
Applications (single and multi-phonon excitations)
SCCM, MPM, DDM etc. predict K=4 double gamma statesshould be widespread in well-deformed rare-earth region.
Prog. Theor. Phys., 76 (1986), 93 ; 78 (1987) 591NPA 487 (1988) 77
Various model predictions for double-gamma states are controversial....
19
Applications (single and multi-phonon excitations)
SCCM, MPM, DDM etc. predict K=4 double gamma statesshould be widespread in well-deformed rare-earth region.
Prog. Theor. Phys., 76 (1986), 93 ; 78 (1987) 591NPA 487 (1988) 77
QPNM predicts K=4 double gamma statesshould exist only in a few special cases (164Dy, 166Er, 168Er)
PRC 51 (1995) 551
Various model predictions for double-gamma states are controversial....
20
Applications (single and multi-phonon excitations)
Various model predictions for double-gamma states are controversial....
SCCM, MPM, DDM etc. predict K=4 double gamma statesshould be widespread in well-deformed rare-earth region.
Prog. Theor. Phys., 76 (1986), 93 ; 78 (1987) 591NPA 487 (1988) 77
QPNM predicts K=4 double gamma statesshould exist only in a few special cases (164Dy, 166Er, 168Er)
PRC 51 (1995) 551
Pure K=0 double gamma states should not exist.Their position depends on the anharmonicity..
NPA 383 (1982) 205Prog. Theor. Phys., 76 (1986), 93 ; 78 (1987) 591PRC 51 (1995) 551NPA 487 (1988) 77
21
Applications (single and multi-phonon excitations)
22
Anharmonicity of double-gamma vibrations-IBM1 perspective
Applications (single and multi-phonon excitations)
Anharmonicity of double-gamma vibrations-IBM1 perspective « Anharmonicities can only exist for finite boson number
and they are always small if only up to two-body interactions are considered. Thus anharmonicity may be
linked to triaxiality »
J. E. Garcia et al., NPA 637 (1998) 529
23
Applications (single and multi-phonon excitations)
« Anharmonicities can only exist for finite boson number and they are always small if only up to two-body
interactions are considered. Thus anharmonicity may be linked to triaxiality »
J. E. Garcia et al., NPA 637 (1998) 529
J. E. Garcia et al., PRC 61 (2000) 047305
In deformed rare-earth
region χ= -0.4-0.7no substantionalanharmonicity
observed
24
Anharmonicity of double-gamma vibrations-IBM1 perspective
Applications (single and multi-phonon excitations)
Quartic terms needed…J. E. Garcia et al., PRC 62 (2000) 064309
An IBM fit of 166Er
ACM beta-rigid calculations
M. A. Caprio, Phys. Lett. B 672 (2009) 396
25
Anharmonicity of double-gamma vibrations- ACM perspective
Applications (single and multi-phonon excitations)
26
Anharmonicity of double-gamma vibrations- ACM perspective
ACM beta-rigid calculations
M. A. Caprio, Phys. Lett. B 672 (2009) 396
With the onset of triaxiality (increasing ξ)the two-phonon energy anharmonicities evolvefrom slightly negative (Eγγ /Eγ smaller than 2) for
ξ =0 to positive (Eγγ /Eγ larger than 2).
Applications (single and multi-phonon excitations)
With the onset of triaxiality (increasing ξ)the two-phonon energy anharmonicities evolvefrom slightly negative (Eγγ /Eγ smaller than 2) for
ξ =0 to positive (Eγγ /Eγ larger than 2).
The anharmonicity of K=0+ state rises more rapidlythan that for K=4+ state.
27
Anharmonicity of double-gamma vibrations- ACM perspective
ACM beta-rigid calculations
M. A. Caprio, Phys. Lett. B 672 (2009) 396
Applications (single and multi-phonon excitations)
Axially symmetric regime
28
B
Applications (single and multi-phonon excitations)
Negligible anharmonicitiesAppearance of beta vib. state for smaller alpha
Full dynamics (including beta degree of freedom) ACM calculations
B B
D. J. Rowe et al., PRC 79 (2009) 054304
B
Axially symmetric regime Gamma excitation energies increase with increasing α
29SO(5) centrifugal stretching occurs for low-energy beta and gamma bands
B
B
B
Negligible anharmonicitiesAppearance of beta vib. state for smaller alpha
Applications (single and multi-phonon excitations)
D. J. Rowe et al., PRC 79 (2009) 054304
Gamma and beta excitation energies increase with increasing alpha, chi and kappa
(approaching the adiabalic limit of the BM)
B B B
Full dynamics (including beta degree of freedom) ACM calculations
D. J. Rowe et al., PRC 79 (2009) 054304
30
Rigid triaxial description of 106Mo K. Shizuma, Z. Phys. A 311 (1983) 71
XAxially symmetric description of 106Mo A. Guessous, PRL 75 (1995) 2280but soft with respect to triaxial deformation.
Small parameter κ required to describeharmonic double-gamma K=4 state
Gamma band appears higher in energy
106Mo
Applications (single and multi-phonon excitations)
B
K=4 harmonic double-gamma vibration
31
Applications (single and multi-phonon excitations)
106MoX
Small parameter κ required to describeharmonic double-gamma K=4 state
Gamma band appears higher in energy
B
Rigid triaxial description of 106Mo K. Shizuma, Z. Phys. A 311 (1983) 71
Axially symmetric description of 106Mo A. Guessous, PRL 75 (1995) 2280but soft with respect to triaxial deformation.
K=4 harmonic double-gamma vibration
Triaxial regime
32
G. s. centrifugal stretching for low-energygamma bands
Large anharmonicities...
Applications (single and multi-phonon excitations)
Centrifugal stretching effects occurs even in the gamma-stabilized situation
M. A. Caprio., PRC 72 (2005) 054323
B B B
1,0 1,2 1,4 1,6 1,8 2,01,8
2,0
2,2
2,4
2,6
2,8
3,0
3,2
3,4
E(K=0)/E
E(K=4)/E
B=70, =0.8, =3
33
K=4, K=0 anharmonic double-gamma vibrations identified in 166ErP. E. Garrett et al., PRL 78 (1997) 24
A low-lying beta vibration identified in 166ErP. E. Garrett et al., Phys. Lett. B 400 (1997) 250
G. Thiamova, Int. J. of Atomic and Nuclear Physics, to be published…
166Er
Applications (single and multi-phonon excitations)
B
34
166Er
G. Thiamova, Int. J. of Atomic and Nuclear Physics, to be published…
Applications (single and multi-phonon excitations)
B
K=4, K=0 anharmonic double-gamma vibrations identified in 166ErP. E. Garrett et al., PRL 78 (1997) 24
A low-lying beta vibration identified in 166ErP. E. Garrett et al., Phys. Lett. B 400 (1997) 250
35
Applications (single and multi-phonon excitations)164Dy
B
K=4 anharmonic double-gamma vibration identified in 164Dy
B(E2, 2173 2 2γ) uncertain
K=4 is not a pure double-gamma vibration…
F. Corminboeuf et al., PRC 56 (1997) R1201
36
164DyApplications (single and multi-phonon excitations)
B
K=4 anharmonic double-gamma vibration identified in 164Dy
B(E2, 2173 2 2γ) uncertain
K=4 is not a pure double-gamma vibration…
F. Corminboeuf et al., PRC 56 (1997) R1201
-ACM and IBM provide basically identical results for realistic boson numbers.
- ACM is a harmonic model in the axially symmetric regime.
-Large anharmonicities can be accomodated in the ACM in the triaxial regime and similarly in the IBM O(6) beta-rigid model. -A large amount of centrifugal stretching for low-lying gamma/beta bands. As a result, large anharmonicities (as observed in 166Er) are underestimated.
-More ACM calculations for divers Hamiltonians needed. -Details of the description or a fundamental failure of the quadrupole degrees of freedom?
« If the large amount of centrifugal stretching effect were shown to persistfor all reasonable ACM Hamiltonians (giving low-lying beta and gamma bands), itwould call into question the consistency of interpreting low-lying excited bands asbeta and gamma bands, when the corresponding centrifugal stretching effects areobserved to be small. »
Collaborators: D. J. Rowe, M. A. Caprio, J. L. Wood 37
Conclusions
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