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Is there a preferred direction in the Universe

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

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Is there a preferred direction in the Universe

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  1. 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

  2. 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

  3. CFA Survey 1986

  4. CFA Survey 1986

  5. CMBR 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

  6. CMBR Probe WMAP

  7. WMAP multi-frequency maps Ka band 33 GHz K band 23 GHz Q band 41 GHz W band 94 GHz V band 61 GHz

  8. DT(q,f) = Temperature Fluctuations about the mean Two Point Correlation Function Statistical isotropy implies

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

  10. TT Cross Power Spectrum

  11. 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

  12. 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

  13. Extraction of Preferred Axis Imagine dT as a wave function y Maximize the angular momentum dispersion  Oliveira-Costa et al 2003

  14. 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

  15. The preferred axis for both • Quadrupole and • Octopole points roughly in the direction (l,b)  (-110o,60o) in Virgo Constellation

  16. 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

  17. 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

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

  19. 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

  20. 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) 2 |RM - <RM>| > 6 rad/m 2 <RM> = 6 rad/m

  21. Distribution of RM The cut eliminates the data near the central peak

  22. The radio dipole axis also points towards Virgo Jain and Ralston, 1999

  23. Anisotropy in Extragalactic Radio Polarizations beta = polarization offset angle Using the cut |RM - <RM>| > 6 rad/m2

  24. Anisotropy in Extragalactic Radio Polarizations Using the cut |RM - <RM>| > 6 rad/m2 Galactic Coordinates

  25. Anisotropy in Extragalactic Radio Polarizations A generalized (RM dependent) statistic indicates that the entire data set shows dipole anisotropy Equatorial Coordinates

  26. Possible Explanation 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

  27. HutsemékersEffect 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

  28. HutsemékersEffect 1<z<2.3 Equatorial Coordinates

  29. 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

  30. Statistic qk, k=1…nv 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 Diand the mean angleq Statistic Jain, Narain and Sarala, 2003

  31. 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 < 2%) • High redshift sample (z > 1)

  32. Significance Level

  33. Significance Level

  34. Significance Level Large redshifts (z > 1) show alignment over the entire sky

  35. Alignment Statistic (z > 1)

  36. Alignment 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

  37. Possible 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

  38. 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

  39. Preferred Axis Optical axis is the eigenvector of S with maximum eigenvalue

  40. Alignment Statistic Preferred axis points towards (or opposite) to Virgo Degree of Polarization < 2%

  41. Prob. for pairwise coincidences Ralston and Jain, 2003

  42. 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. 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

  43. Anisotropy in Extragalactic Radio Polarizations sin(2b) < 0 + sin(2b) > 0  Using the cut |RM - <RM>| > 6 rad/m2

  44. Significance Level of Radio Anisotropy

  45. Radiation propagating over cosmological distances also probes isotropy of the Universe • CMBR • Radiation from distant AGNs

  46. 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

  47. APM Survey 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

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