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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

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 supergalactic 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

CFA Survey 1986 homogeneous and isotropic

CFA Survey 1986 homogeneous and isotropic

CMBR homogeneous and isotropic

What does CMBR imply about the isotropy of the universe?

WMAP released very high resolution data in march 2003

Total number of pixels = 512 x 512 x 12

The data is available at 5 frequencies

There is considerable contamination from foreground emissions which complicate the interpretation of data

CMBR Probe WMAP homogeneous and isotropic

WMAP multi-frequency maps homogeneous and isotropic

Ka band 33 GHz

K band 23 GHz

Q band 41 GHz

W band 94 GHz

V band 61 GHz

D homogeneous and isotropicT(q,f) = Temperature Fluctuations about the mean

Two Point Correlation Function

Statistical isotropy implies

If we assume that homogeneous and isotropicDT (and alm) are Gaussian random variables (with 0 mean)then all the statistical information is contained in the two point correlation function

or

TT Cross Power Spectrum homogeneous and isotropic

The power is low at small l (quadrupole l=2) homogeneous and isotropic

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

Cleaned Map homogeneous and isotropic

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

Extraction of Preferred Axis homogeneous and isotropic

Imagine dT as a wave function y

Maximize the angular momentum dispersion

Oliveira-Costa et al 2003

Extraction of Preferred Axis homogeneous and isotropic

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

- The preferred axis for both homogeneous and isotropic
- Quadrupole
and

- Octopole
points roughly in the direction

(l,b) (-110o,60o) in Virgo Constellation

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

CMBR Dipole direction (pointing towards Virgo)

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

Physical Explanations direction (pointing towards Virgo)

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
- (Berera, Buniy and Kephart, 2003)
- Sunyaev Zeldovich effect due to local supercluster
(Abramo and Sodre, 2003)

Anisotropy in Radio Polarizations direction (pointing towards Virgo)

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

b direction (pointing towards Virgo) = 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)

2

|RM - <RM>| > 6 rad/m

2

<RM> = 6 rad/m

Distribution of RM direction (pointing towards Virgo)

The cut eliminates the data near the central peak

The radio dipole axis also points towards Virgo direction (pointing towards Virgo)

Jain and Ralston, 1999

Anisotropy in Extragalactic Radio Polarizations direction (pointing towards Virgo)

beta = polarization offset angle

Using the cut |RM - <RM>| > 6 rad/m2

Anisotropy in Extragalactic Radio Polarizations direction (pointing towards Virgo)

Using the cut |RM - <RM>| > 6 rad/m2

Galactic Coordinates

Anisotropy in Extragalactic Radio Polarizations direction (pointing towards Virgo)

A generalized (RM dependent) statistic indicates that the entire data set shows dipole anisotropy

Equatorial Coordinates

Possible Explanation direction (pointing towards Virgo)

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

- Rotation in polarization =gfgg (Df)
- f = change in the pseudoscalar field along the path

gfgg < 10 -11 GeV-1

Hutsem direction (pointing towards Virgo)ékersEffect

Optical Polarizations of QSOs appear to be locally aligned with one another. (Hutsemékers, 1998)

1<z<2.3

A very strong alignment is seen in the direction of Virgo cluster

Statistical Analysis direction (pointing towards Virgo)

- 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

Statistic direction (pointing towards Virgo)

qk, k=1…nv are the polarizations of the nv nearest neighbours of the source i

D ki = contribution due to parallel transport

- Maximizing di(q) with respect to q gives a measure of alignment Diand the mean angleq

Statistic

Jain, Narain and Sarala, 2003

Alignment Results direction (pointing towards Virgo)

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 < 2%)
- High redshift sample (z > 1)

Significance Level direction (pointing towards Virgo)

Significance Level direction (pointing towards Virgo)

Significance Level direction (pointing towards Virgo)

Large redshifts (z > 1) show alignment over the entire sky

Alignment Statistic (z > 1) direction (pointing towards Virgo)

Alignment Results direction (pointing towards Virgo)

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

Possible Explanation direction (pointing towards Virgo)

Optical Alignment can also be explained by a pseudoscalar field.

As the EM wave passes through large scale magnetic field, photons (polarized parallel to transverse magnetic field) decay into pseudoscalars

The wave gets polarized perpendicular to the transverse magnetic field

But we require magnetic field on cosmologically large distance scales

Jain, Panda and Sarala, 2002

Preferred Axis direction (pointing towards Virgo)

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

Preferred Axis direction (pointing towards Virgo)

Optical axis is the eigenvector of S with maximum eigenvalue

Alignment Statistic direction (pointing towards Virgo)

Preferred axis points towards (or opposite) to Virgo

Degree of Polarization < 2%

Prob. for pairwise coincidences direction (pointing towards Virgo)

Ralston and Jain, 2003

Concluding Remarks direction (pointing towards Virgo)

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.

Radio anisotropy may also arise due to some local unknown effect

However it is not possible to attribute optical alignment to a local effect

Future observations will hopefully clarify the situation

Anisotropy in Extragalactic Radio Polarizations direction (pointing towards Virgo)

sin(2b) < 0 +

sin(2b) > 0

Using the cut |RM - <RM>| > 6 rad/m2

Significance Level of Radio Anisotropy direction (pointing towards Virgo)

Radiation propagating over cosmological distances also probes isotropy of the Universe

- CMBR
- Radiation from distant AGNs

On Large scale it is assumed that Universe is Isotropic and Homogeneous

The 3-dim space appears the same in all directions and at all locations

One way to test for isotropy and homogeneity is by observing the density of matter (galaxies) in different directions and positions

Angular correlation function

or 3-D correlation function

APM Survey Homogeneous

100 degrees by 50 degrees around the South Galactic Pole

Intensities scaled to the number of galaxies

blue, green and red for bright, medium and faint galaxies

The APM survey has about 5 million galaxies Homogeneous

It gives an accurate measure of the angular two point correlation function to about 10 degrees

The results agree reasonably well with the LCDM model with

WL = 0.7

Dodelson (2003)

Maddox et al (1990)

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