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
• Low order multipoles of CMBR

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On distance scales of less than 100 Mpc the
Universe is not homogeneous and isotropic
Most galaxies in our vicinity lie in a plane (the
supercluster plane) which is approximately
perpendicular to the galactic plane.
The Virgo cluster sits at the center of this disc
like structure
On larger distance scales the universe appears
isotropic
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CMBR
CMBR is isotropic to a very good approximation
What does CMBR fluctuations imply about the
isotropy of the universe?
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TT Cross Power Spectrum
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The power is low at small l (quadrupole l2)
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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Cleaned Map
Quadrupole
Octopole
All the hot and cold spots of the Quadrupole and
Octopole lie in a plane, inclined at approx 30o
to galactic plane
Oliveira-Costa et al 2003
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Extraction of Preferred Axis
Imagine dT as a wave function y
Maximize the angular momentum dispersion
?
Oliveira-Costa et al 2003
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Extraction of Preferred Axis
Alternatively Define
k 1 3, m -l l
Preferred frame eka is obtained by Singular Value
Decomposition
ea represent 3 orthogonal axes in space
The preferred axes is the one with largest
eigenvalue La
Ralston, Jain 2003
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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 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 Explanations
Many 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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Anisotropy in Radio Polarizations
Radio Polarizations from distant AGNs show a
dipole anisotropy

• Offset angle b c - y
• q(l2 ) c (RM) l2
• RM Faraday Rotation Measure
• c IPA (Polarization at source)

b shows a Dipole ANISOTROPY
Birch 1982 Jain, Ralston, 1999 Jain, Sarala, 2003
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b polarization offset angle
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)
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RM - ltRMgt gt 6 rad/m
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ltRMgt 6 rad/m
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Distribution 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 Polarizations
beta polarization offset angle
Using the cut RM - ltRMgt gt 6 rad/m2
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Anisotropy in Extragalactic Radio Polarizations
Using the cut RM - ltRMgt gt 6 rad/m2
Galactic Coordinates
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Anisotropy in Extragalactic Radio Polarizations
A generalized (RM dependent) statistic indicates
that the entire data set shows dipole anisotropy
Equatorial Coordinates
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Hutsemékers Effect
Optical Polarizations of QSOs appear to be
locally aligned with one another. (Hutsemékers,
1998)
1ltzlt2.3
A very strong alignment is seen in the direction
of Virgo cluster
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Hutsemékers Effect
1ltzlt2.3
Equatorial Coordinates
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Statistical 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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Statistic
qk, k1nv are the polarizations of the nv
nearest neighbours of the source i
D k?i contribution due to parallel transport

• Maximizing di(q) with respect to q gives a
  measure of alignment Di and the mean
  angle q

Statistic
Jain, Narain and Sarala, 2003
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Alignment Results
We find a strong signal of redshift dependent
alignment in a data sample of 213 quasars
The strongest signal is seen in

• Low polarization sample (p lt 2)
• High redshift sample (z gt 1)

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Significance Level
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Significance Level
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Significance Level
Large redshifts (z gt 1) show alignment over the
entire sky
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Alignment Statistic (z gt 1)
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Alignment Results
Strongest correlation is seen at low
polarizations ( p lt 2) at distance scales of
order Gpc
Large redshifts z gt 1 show alignment over the
entire sky
Jain, Narain and Sarala, 2003
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Preferred Axis
Two point correlation
Define the correlation tensor
Define
where
S is a unit matrix for an isotropic uncorrelated
sample
is the matrix of sky locations
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Preferred Axis
Optical axis is the eigenvector of S with maximum
eigenvalue
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Alignment Statistic
Preferred axis points towards (or opposite) to
Virgo
Degree of Polarization lt 2
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Prob. for pairwise coincidences
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
Ralston and Jain, 2003
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Physical Explanation

• 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

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Physical Explanation
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
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Physical Explanation
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)
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Light Scalars

• 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
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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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We are basically interested in electromagnetic
waves propagating over astrophysical or
cosmological distances in the presence of a
background magnetic field.
As the EM wave passes through large scale
background magnetic field, photons (polarized
parallel to transverse magnetic field) mix with
pseudoscalars
This leads to reduced intensity of wave if the
incident pseudoscalar flux is assumed negligible
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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)
This may also be partially responsible for
dimming of distant supernovae (Csaki,
Kaloper and Terning, 2002)
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Polarization
The wave gets polarized perpendicular to the
transverse magnetic field since only 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
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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 lt 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
lt 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 scales
Background magnetic field for the case of Virgo
supercluster is roughly 0.1 ?G, distance 1-10
Mpc Plasma 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 mixing

• We have considered this mixing in great detail
  so that it can be tested in future observations
• Uniform background
• Turbulent 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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Stokes Parameters as a function of ? (we set I
1)
Uniform Background At source Q0, U0.4, V 0.1
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Degree of Polarization as a function of the
distance of propagation The 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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Background pseudoscalar field
A background pseudoscalar (scalar) field also
leads to a rotation of the polarization of the
wave

• Rotation in polarization gfgg (D f)
• f change in the pseudoscalar field along the
  path

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Possible Explanation of Radio Anisotropy

An anisotropically distributed background
pseudoscalar field f of sufficiently large
strength can explain the observations
Pseudoscalar field at source
To account for the RM dependence
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Concluding Remarks
There 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 Remarks
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.
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