is there a preferred direction in the universe
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Is there a preferred direction in the Universe. P. Jain, IIT Kanpur. There appear to be several indications of the existence of a preferred direction in the Universe (or a breakdown of isotropy). Optical polarizations from distant AGNs Radio polarizations from distant AGNs - PowerPoint PPT PresentationTRANSCRIPT
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Is there a preferred direction in the UniverseIs there a preferred direction in the Universe
P. Jain, IIT Kanpur
There appear to be several indications of the existence of a preferred direction in the Universe (or a breakdown of isotropy)
Optical polarizations from distant AGNsRadio polarizations from distant AGNsLow order multipoles of CMBR
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On distance scales of less than 100 Mpc the Universe is not homogeneous and isotropic
The Virgo cluster sits at the center of this disc like structure
Most galaxies in our vicinity lie in a plane (the supercluster plane) which is approximately perpendicular to the galactic plane.
On larger distance scales the universe appears isotropic
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CMBRCMBR
What does CMBR fluctuations imply about the isotropy of the universe?
*)1( lmlml aallC
),(),(2
l
l
lmlmlmYaT
CMBR is isotropic to a very good approximation
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TT Cross Power SpectrumTT Cross Power Spectrum
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The power is low at small l (quadrupole l=2)
The probability for such a low quadrupole to occur by a random fluctuation is 5%
Oliveira-Costa et al 2003
The Octopole is not small but very planar
Surprisingly the Octopole and Quadrupole appear to be aligned with one another with the chance probability =1/62
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Quadrupole
Octopole
Cleaned Map
Oliveira-Costa et al 2003
All the hot and cold spots of the Quadrupole and Octopole lie in a plane, inclined at approx 30o to galactic plane
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Extraction of Preferred AxisExtraction of Preferred AxisImagine T as a wave function
Maximize the angular momentum dispersion
Oliveira-Costa et al 2003
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Extraction of Preferred AxisExtraction of Preferred Axis
k = 1 …3, m = -l … l
Preferred frame ek is obtained by Singular Value Decomposition
e represent 3 orthogonal axes in space
The preferred axes is the one with largest eigenvalue
Ralston, Jain 2003
Alternatively Define
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The preferred axis for both Quadrupole and Octopole points roughly in the direction (l,b) (-110o,60o) in Virgo Constellation
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Hence WMAP data suggests the existence of a preferred direction (pointing towards Virgo)
We (Ralston and Jain, 2003) show that there is considerable more evidence for this preferred direction
CMBR dipole
Anisotropy in radio polarizations from distant AGNs
Two point correlations in optical polarizations from AGNs
Also point in this directionAlso point in this direction
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CMBR Dipole
The dipole is assumed to arise due to the local (peculiar) motion of the milky way, arising due to local in-homogeneities
The observed dipole also points in the direction of Virgo
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Physical ExplanationsPhysical ExplanationsMany explanations have been proposed for the anomalous behavior of the low order harmonics
Non trivial topology (Luminet, Weeks, Riazuelo, Leboucq and Uzan, 2003)
Anisotropic Universe due to background magnetic field (Berera, Buniy and Kephart, 2003)
Sunyaev Zeldovich effect due to local supercluster (Abramo and Sodre, 2003)
A satisfactory explanation of the observations is still lacking
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Offset angle RM)
RM : Faraday Rotation Measure
= IPA (Polarization at source)
Anisotropy in Radio PolarizationsAnisotropy in Radio Polarizations
shows a Dipole ANISOTROPY
Radio Polarizations from distant AGNs show a dipole anisotropy
Birch 1982Jain, Ralston, 1999Jain, Sarala, 2003
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Likelihood Analysis The Anisotropy
is significant at 1% in full (332 sources) data set and 0.06% after making a cut in RM (265 sources)
RM - <RM>| > 6 rad/m
<RM> = 6 rad/m
= polarization offset angle
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Distribution of RMDistribution of RM
The cut eliminates the data near the central peak
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The radio dipole axis also points towards Virgo
Jain and Ralston, 1999
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Anisotropy in Extragalactic Radio PolarizationsAnisotropy in Extragalactic Radio Polarizations
beta = polarization offset angle
Using the cut |RM - <RM>| > 6 rad/m2
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Anisotropy in Extragalactic Radio PolarizationsAnisotropy in Extragalactic Radio Polarizations
Using the cut |RM - <RM>| > 6 rad/m2
Galactic Coordinates
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Equatorial Coordinates
Anisotropy in Extragalactic Radio PolarizationsAnisotropy in Extragalactic Radio PolarizationsA generalized (RM dependent) statistic indicates that the entire data set shows dipole anisotropy
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HutsemHutseméékerskers EffectEffectOptical Polarizations of QSOs appear to be locally aligned with one another. (Hutsemékers, 1998)
A very strong alignment is seen in the direction of Virgo cluster
1<z<2.3
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HutsemHutseméékerskers EffectEffect
Equatorial Coordinates
1<z<2.3
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Statistical AnalysisStatistical Analysis A measure of alignment is obtained by comparing
polarization angles in a local neighborhood
The polarizations at different angular positions are compared by making a parallel transport along the great circle joining the two points
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•Maximizing di() with respect to gives a measure of alignment Di and the mean angle
StatisticStatistic
k, k=1…nv are the polarizations of the nv nearest neighbours of the source i
ki = contribution due to parallel transport
Statistic Jain, Narain and Sarala, 2003
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We find a strong signal of redshift dependent alignment in a data sample of 213 quasars
Alignment ResultsAlignment Results
Low polarization sample (p < 2%) High redshift sample (z > 1)
The strongest signal is seen in
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Significance LevelSignificance Level
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Significance LevelSignificance Level
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Significance LevelSignificance Level
Large redshifts (z > 1) show alignment over the entire sky
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Alignment Statistic (z > 1)Alignment Statistic (z > 1)
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Alignment ResultsAlignment Results
Strongest correlation is seen at low polarizations ( p < 2%) at distance scales of order Gpc
Large redshifts z > 1 show alignment over the entire sky
Jain, Narain and Sarala, 2003
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Preferred AxisPreferred AxisTwo point correlation
Define the correlation tensor
Define
where
is the matrix of sky locations
S is a unit matrix for an isotropic uncorrelated sample
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Preferred AxisPreferred Axis
Optical axis is the eigenvector of S with maximum eigenvalue
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Alignment StatisticAlignment Statistic
Preferred axis points towards (or opposite) to Virgo
Degree of Polarization < 2%
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dipole quad octo radio optical
dipole 0.020 0.061 0.042 0.024
quad 0.015 0.023 0.004
octo 0.059 0.026
radio 0.008
Prob. for pairwise coincidencesProb. for pairwise coincidences
Ralston and Jain, 2003
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A satisfactory explanation of the observations is so far not available
It is possible that the universe may not be isotropic even at cosmological scales. One should then explore generalization of the FRW metric
the large scale anisotropies could arise due to :
• propagation in a large scale anisotropic medium• The active galactic nuclei may be intrinsically correlated on very large distance scales. Similarly the CMBR quadrupole and octopole may be aligned at the source
Physical ExplanationPhysical Explanation
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Alternatively the anisotropies could arise due to the local inhomogeneous distribution of matter
This possibility cannot be ruled out for the CMBR and radio anisotropies but is unlikely to account for the large scale optical correlations, which is a redshift dependent effect
Physical ExplanationPhysical Explanation
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The observations may also represent a fundamental violation of Lorentz invariance
Lorentz invariance has been observed to be a very good symmetry of nature.
Theoretically we expect that it is violated due to quantum gravity effects.
We expect violations of order
(M Susy/M Planck)2 (Jain, Ralston 2005)
Physical ExplanationPhysical Explanation
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We have been exploring the possibility that the effects may be explained by a light scalar (or pseudoscalar)
Very light mass pseudoscalars (or scalars) are predicted by many theories beyond the Standard Model
Axion (Peccei-Quinn) Supergravity String theory
A very light scalar or pseudoscalar may also be required to explain dark energy
A common model for dark energy is a scalar field slowly rolling towards its true vacuum
Light ScalarsLight Scalars
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Coupling to Photons
• Such a scalar field will have an effective coupling to photons
• It does not matter whether is a scalar or a pseudoscalar
• If is a scalar then this interaction breaks parity but parity is not a symmetry of nature.
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This leads to reduced intensity of wave if the incident pseudoscalar flux is assumed negligible
As the EM wave passes through large scale background magnetic field, photons (polarized parallel to transverse magnetic field) mix with pseudoscalars
We are basically interested in electromagnetic waves propagating over astrophysical or cosmological distances in the presence of a background magnetic field.
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This may also be partially responsible for dimming of distant supernovae (Csaki, Kaloper and Terning, 2002)
The reduction in intensity due to pseudoscalar photon mixing in the local supercluster magnetic field may explain the anomalous CMBR quadrupole and octopole
(Jain and Saha, work in progress)
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The wave gets polarized perpendicular to the transverse magnetic field sinceonly the component parallel to the background magnetic field mixes with pseudoscalars
This may explain the optical alignment
However we require magnetic field coherent on cosmologically large distance scales
Polarization
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Limit on the coupling
For the invisible axion the current limit on the Peccei-Quinn symmetry breaking scale is 109 GeV,
Mass < 0.01 eV (PDG)
This particle gives very little contribution to mixing for galactic or intergalactic propagation.
It may contribute in regions of strong magnetic fields and plasma density.
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We are interested in a pseudoscalar whose mass may be much smaller
g < 6 x 10-11 /GeV (PDG)if we assume that the mass is negligible
We will assume that its mass is smaller or comparable to the plasma density of the medium
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Typical scalesBackground magnetic field for the case of Virgo supercluster is roughly 0.1 G, distance 1-10 MpcPlasma density 10-6 cm-3
For intergalactic propagation it may be reasonable to assume many domains of size 1 Mpc and B ≈ 0.005 G Plasma density 10- 8 cm-3
We are interested in the frequency regime from radio to optical, = 10- 5 – 1 eV
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Pseudoscalar Photon mixingPseudoscalar Photon mixing
We have considered this mixing in great detail so that it can be tested in future observations
Uniform backgroundTurbulent background (Jain, Panda, Sarala, 2002)Slowly varying background (background magnetic field direction fixed)
(Das, Jain, Ralston, Saha, 2004)Slowly varying background with the direction of magnetic field varying with distance.
(Das, Jain, Ralston, Saha, 2004)
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Degree of Polarization as a function of l (or )
Uniform Background
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Uniform BackgroundAt source Q=0, U=0.4, V = 0.1
Stokes Parameters as a function of (we set I = 1)
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Degree of Polarization as a function of the distance of propagationThe wave is unpolarized at source
Resonant Mixing
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Stokes parameter V as a function of Q for several different parameters (varying background magnetic field direction)
V
Q
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A background pseudoscalar (scalar) field also leads to a rotation of the polarization of the wave
Background pseudoscalar field
Rotation in polarization =g (
change in the pseudoscalar field along the path
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Possible Explanation of Radio Possible Explanation of Radio AnisotropyAnisotropy
An anisotropically distributed background pseudoscalar field of sufficiently large strength can explain the observations
To account for the RM dependence
Pseudoscalar field at source
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Concluding RemarksConcluding RemarksThere appears to be considerable evidence that there is a preferred direction in the Universe pointing towards Virgo
However the CMBR observations may also be explained in terms of some local distortion of microwave photons due to supercluster.
The physical mechanism responsible for this is not known so far.
We are considering the possibility that it may be explained due to conversion of photons into pseudoscalars due to propagation through local supercluster magnetic field.
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Concluding RemarksConcluding Remarks
It is not possible to attribute optical alignment to a local effect since it is intrisically redshift dependent.We can explain this in terms of pseudoscalar photon mixing provided there exist magnetic fields coherent on cosmological distance scales
Future observations will hopefully clarify the situation
Radio anisotropy may also arise due to some local unknown effect. However it is difficult to find a physical mechanism which can accomplish this.
An anisotropically distributed background pseudoscalar field may explain this effect.