universe

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

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 supergalactic plane) which is approximately perpendicular to the galactic plane.

On larger distance scales the universe appears isotropic

CFA Survey 1986

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

CMBRCMBR

What does CMBR imply about the isotropy of the universe?

CMBR Probe WMAP

K band 23 GHz

Ka band 33 GHz

Q band 41 GHz

V band 61 GHzW band 94 GHz

WMAP multi-frequency mapsWMAP multi-frequency maps

),(),(2

l

l

lmlmlmYaT

TTemperature Fluctuations about the mean

Two Point Correlation Function

Statistical isotropy implies

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

or

*)1( lmlml aallC

TT Cross Power SpectrumTT Cross Power Spectrum

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

Quadrupole

Octopole

Cleaned Map


All the hot and cold spots of the Quadrupole and Octopole lie in a plane, inclined at approx 30o to galactic plane

Extraction of Preferred AxisExtraction of Preferred AxisImagine T as a wave function

Maximize the angular momentum dispersion


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

The preferred axis for both 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 directionAlso point in this direction

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

Physical ExplanationsPhysical 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 (Berera, Buniy and Kephart, 2003)

Sunyaev Zeldovich effect due to local supercluster (Abramo and Sodre, 2003)

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

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

Distribution of RMDistribution of RM

The cut eliminates the data near the central peak

The radio dipole axis also points towards Virgo

Jain and Ralston, 1999

Anisotropy in Extragalactic Radio PolarizationsAnisotropy in Extragalactic Radio Polarizations

beta = polarization offset angle

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



Galactic Coordinates

Equatorial Coordinates

Anisotropy in Extragalactic Radio PolarizationsAnisotropy in Extragalactic Radio PolarizationsA generalized (RM dependent) statistic indicates that the entire data set shows dipole anisotropy

Possible ExplanationPossible Explanation

An anisotropically distributed background pseudoscalar field of sufficiently large strength can explain the observations

To account for the RM dependence

Rotation in polarization =g ( change in the pseudoscalar field along the path

Pseudoscalar field at source

g< 10 -11 GeV-1

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

HutsemHutseméékerskers EffectEffect

Equatorial Coordinates

1<z<2.3

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

•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

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

Significance LevelSignificance Level

Significance LevelSignificance Level

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

Alignment Statistic (z > 1)Alignment Statistic (z > 1)

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

Possible ExplanationPossible Explanation

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 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

Preferred AxisPreferred Axis

Optical axis is the eigenvector of S with maximum eigenvalue

Alignment StatisticAlignment Statistic

Preferred axis points towards (or opposite) to Virgo

Degree of Polarization < 2%

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

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.

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

Future observations will hopefully clarify the situation

Radio anisotropy may also arise due to some local unknown effect


sin(2) < 0 +

sin(2) > 0


Significance Level of Radio Significance Level of Radio AnisotropyAnisotropy

Radiation propagating over cosmological Radiation propagating over cosmological distances also probes isotropy of the Universedistances also probes isotropy of the Universe

CMBR

Radiation from distant AGNs

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

)()()( 21 nnw

Angular correlation function

or 3-D correlation function

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

APM Survey100 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

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

The results agree reasonably well with the CDM model with

Dodelson (2003)Maddox et al (1990)

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radio dipole axis

cut rm

dipole anisotropy birch

sources rm

preferred axes

quadrupole octopole

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