The Cosmic Microwave Background and The Relic Neutrino Background

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The Cosmic Microwave Background andThe Relic
Neutrino Background

• Oral Qualifying Exam

Alexandre Bruno Sousa
May 2002
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Outline

• Introduction
• CMBR Properties
• Recent CMBR Measurements
• The Standard Cosmology
• Is The Universe Flat?
• Future Experiments
• The Relic Neutrino Background
• RNB Properties
• RNB Observation
• Conclusions

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Introduction

• The Cosmic Microwave Background Radiation was
  originally predicted by George Gamow in the late
  1940s to be a necessary consequence of a Universe
  originated according to the Big Bang model.
• It was discovered accidentally by Arno Penzias
  and Robert Wilson in 1965, during studies of the
  radio emissions of the Milky Way.
• The CMBR thermal spectrum is fitted to a high
  degree of accuracy to a Black Body radiation
  spectrum with T3 K

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Introduction

• The CMBR was emitted 400 000 years after the Big
  Bang when radiation decoupled from matter,
  following recombination of protons and electrons
  to form Hydrogen atoms.
• Detailed studies of the CMBR allow us to look
  directly into the features of the surface of last
  scattering, providing insights on several
  cosmological parameters, the curvature and the
  large scale structure of the Universe.

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CMBR Properties

• The CMBR Thermal Spectrum follows a Planckian
  distribution to a very high degree of accuracy.
  Current measurements yield the Black Body
  temperature
• The current CMBR number density is

• The CMBR temperature is remarkably uniform over
  a wide range of angular scales.

• The frequencies of the CMBR anisotropies overlap
  with some galactic emissions which thus
  constitute experimental backgrounds.

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CMBR Anisotropies

• Studies of the small temperature fluctuations in
  the CMBR provide a unique probe of the Universe
  early times. These fluctuations arise due to five
  distinct physical effects
• 1) Our peculiar velocity with respect to the
  cosmic rest frame
• (Dipole Anisotropy).
• 2) Density fluctuations on the last scattering
  surface
• (Sachs-Wolfe effect).
• 3) Fluctuations intrinsic to the radiation field
  itself on the last scattering surface.
• 4) The peculiar velocity of the last scattering
  surface.
• 5) Additional fluctuations from scattering on hot
  electrons if the Universe should be re-ionized
  after decoupling (Sunyaev-Zeldovich effect).

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CMBR Anisotropies
Dipole Anisotropy

• Our movement with respect to the cosmic rest
  frame Doppler shifts the CMBR. The regions we are
  moving towards to appear hotter.
• From this measurements it is possible to
  establish that we are moving with v 3711 Km/s
  towards l 264.14 0.15, b 48.26 0.15.

http//chandra.harvard.edu/photo/map/
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The CMBR Power Spectrum

• The CMBR temperature fluctuations can be expanded
  into spherical harmonics
• Dropping the dipole term, the mean square over
  the whole sky is
• Averaging over all possible positions of a
  randomly placed observer, we find
• The Cl coefficients provide a complete
  statistical description of the temperature
  anisotropies.

• At large l one also finds that the angular size
  of a feature in the sky is inversely
  proportional to the order l of the multipole that
  dominates it

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The CMBR Power Spectrum

• The experimental determination of the Power
  Spectrum follows closely the procedure depicted
  above. One expands a temperature measurement at a
  position p in spherical harmonics
• Where is a window function that accounts
  for the beam pattern seen by the experiment. The
  correlation between signals from two different
  points in the sky is then
• Averaging over all directions separated by an
  angle and over all positions as before, we
  find
• As an example, a gaussian beam profile with FWHM
  qC, transformed into l space, yields the window
  function
• The Power Spectrum calculated from the
  temperature measurements of the sky is model
  independent.

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Recent Measurements of the CMBR
COBE-COsmic Background Explorer

• COBE was launched by NASA in 1989. The CMBR
  anisotropy was measured by the Differential
  Microwave Radiometer (DMR) instrument.
• COBE Angular Resolution
• DMR Measurements at 31.5, 53 and 90 GHz.
• 4 years of data taking.

http//space.gsfc.nasa.gov/astro/cobe/
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Recent Measurements of the CMBR
COBE Results
http//space.gsfc.nasa.gov/astro/cobe/dmr_image.ht
ml

• Precise measurement of the dipole anisotropy
• First measurement of a CMBR intrinsic anisotropy
• 
  
• 
  on a 7º angular scale.

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Recent Measurements of the CMBR
BOOMERanGBaloon Observations Of Millimetric
ExtraGalactic Radiation and Geophysics

• BOOMERanG is a baloon experiment designed to map
  the CMBR over a partial region of the sky with
  increased resolution over COBE/DMR.
• 10 angular resolution gt (40
  times better than COBE/DMR).
• 90, 150, 240 and 400 GHz frequency measurements.
• Sensitivity similar to COBEs
• 10.5 days flight over Antarctica.
• 37 Km altitude.
• Sky coverage 1800 square degrees (3 of the
  sky).

http//www.physics.ucsb.edu/boomerang/
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Recent Measurements of the CMBR
BOOMERanG Payload
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Recent Measurements of the CMBR
BOOMERanG Results-Sky Maps

• The average scale of the temperature fluctuations
  is around 1 degree.

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Recent Measurements of the CMBR
BOOMERanG Results-Power Spectrum

• The Power Spectrum shows a primary peak at l200,
  corresponding to an angular scale of 1º.
• The fit to the data is consistent with a flat
  Universe (to be discussed).

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Recent Measurements of the CMBR
Other Experiments

• MAXIMA (Millimiter Anisotropy eXperiment IMaging
  Array)
• Very similar to BOOMERanG with shorter flights
  and equivalent angular resolution.
• DASI (Degree Angular Scale Interferometer)
• Ground based at the Scott-Amundsen South Pole
  station.
• 20 resolution at 26, 30 and 36 GHz
• CBI (Cosmic Background Imager)
• Ground based 13 element interferometer at S.
  Pedro de Atacama, Chile.
• 5-1º resolution at 26-36 GHz

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Recent Measurements of the CMBR
Other Experiments-Results
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The Standard Cosmology

• The Big Bang model, now considered the Standard
  Cosmology, describes a homogeneous and isotropic
  expanding Universe consistent with the
  Cosmological Principle. The line element for any
  space-time consistent with this principle can be
  written on a Friedmann-Robertson-Walker form
• In spherical coordinates
• k is the constant curvature and it is determined
  by the spatial geometry of the Universe
• In such Universe, two particles separated by a
  distance l , which grows proportionally to a(t),
  will have a corresponding recessional velocity

• We can define a dimensionless density parameter
• where is the density of a flat
  Universe.

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The Standard Cosmology
Shortcomings of the Standard Cosmology

• 1) Horizon Problem The Universe is homogeneous
  and isotropic on scales much greater than the
  horizon (CMBR measurements are a clear proof).
• 2) Flatness Problem The density of the present
  universe is within one order of magnitude of the
  critical density . However, it can be
  shown that deviations from grow with
  time
• In the Standard Cosmology, this means that
  was fine-tuned to within
• at the Planck time .
• 3) Density fluctuation Problem It is believed
  that galaxies and clusters of galaxies evolved by
  gravitational instability from small density
  fluctuations in the early universe. The required
  magnitude of fluctuations on galactic scales at
  the Planck epoch is
• 4) Dark Matter Problem Should the density of the
  Universe be very close to the critical density,
  non-baryonic matter must dominate the Universe.
  The nature of this Dark Matter is still unknown.
  

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Is the Universe Flat?
The Inflationary Paradigm

• Formulated by Alan Guth in 1981, the Inflationary
  Paradigm postulates that the very early Universe
  underwent a period of very rapid expansion. The
  expansion factor is

• As a result of Inflation, regions initially in
  causal contact are blown up to sizes much greater
  than the present Hubble radius.
• The curvature of the Universe is increased by an
  enormous factor, so that it becomes
  indistinguishable from a flat Universe.
• Both the Horizon and the Flatness problems are
  solved if
• Small density perturbations are produced due to
  quantum fluctuations of gravitational fields
  during Inflation, a possible solution for the
  density fluctuation problem.

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Is the Universe Flat?
Cosmological Parameters

• The Power Spectrum of the CMBR (i.e. the Cl
  coefficients) depends on several cosmological
  parameters
• The total density
  parameter of the Universe.
• The baryon density
  parameter.
• The Cold Dark Matter
  density parameter.
• The Cosmological Constant
  density parameter.
• The spectral index of
  scalar fluctuations.
• The Hubble Constant.

• The following animations show how the variation
  of these parameters affect the angular power
  spectrum.

http//www.hep.upenn.edu/max/cmb/movies.html
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Is the Universe Flat?
Results

• The current best estimates for the cosmological
  parameters from CMBR measurements come from
  BOOMERanG.

Best Fit

• Either alone or combined with the LSS Survey and
  the Supernovae Survey, the CMBR measurements
  strongly indicate that we live in a flat or
  nearly flat Universe, consistent with the
  inflationary scenarios.

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Future Experiments
MAP-Microwave Anisotropy Probe

• The natural successor of COBE, MAP was launched
  in 2001 to an Earth-Sun lagrangian point orbit.
• 2 years of data taking.
• 15 minimum angular resolution over a 22-90 GHz
  frequency range.

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Future Experiments
PLANCK

• Scheduled for launch in early 2007, the PLANCK
  survey of the CMBR will produce its most accurate
  and extensive map.
• Orbit similar to the MAP orbit.
• 5 angular resolution
• 30-850 GHz frequency range (almost complete
  extraction of foregrounds).
• Very high sensitivity

http//astro.estec.esa.nl/SA-general/Projects/Plan
ck/
RF receiver (30-100 GHz)
Bolometer(100-850GHz)
Planck detector
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Future Experiments
PLANCK-Predicted Results

• Able to monitor and remove galactic and
  extragalactic foregrounds, the PLANCK Survey
  will measure the statistical properties of the
  CMBR to high accuracy, establishing very strong
  cosmological constraints and dramatically
  increasing our knowledge of the early Universe
  and its evolution.

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The Relic Neutrino Backgound
Introduction

• Neutrinos are probably one of the most abundant
  components of the Universe.
• A sea of Relic Neutrinos decoupled from the rest
  of the matter within the first seconds after the
  Big Bang.
• The Universe should also be filled with Relic
  Neutrinos generated by Supernovae explosions.
• Ultra High Energy Relic Neutrinos could be
  generated by AGNs (Active Galactic Nuclei) and
  sources of Gamma Ray Bursts.

Relic Neutrino Sea decouples
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RNB Properties

• Before neutrino decoupling, the neutrinos are in
  equilibrium through weak interactions such as
• After decoupling, the neutrinos are expected to
  have a similar temperature to the one from the
  CMBR, but Reheating occurs, changing the value of
  
• Before pair annihilation
• After pair annihilation
• Since the total entropy density for particles in
  equilibrium is conserved

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RNB Properties

• The present number density of neutrinos for a
  single family is
• If then the present velocity of
  the relic neutrinos is
• The neutrino contribution to the total mass
  density in units of the critical density is given
  by
• The present upper limit on the neutrino mass from
  cosmological considerations arises from CMBLSS
  results
• This present lower upper limit for the neutrino
  mass obtained in laboratory comes from the
  Heidelberg-Moscow experiment, assuming Majorana
  neutrinos

Wang, Tegmark Zaldarriaga (astro-ph/0105091)
m v (0.05 - 0.84) eV (95 C.L.)
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RNB Observation

• Due to the low energies involved, direct
  observation of the relic neutrino sea is beyond
  present technological capabilities. However,
  indirect observation may be possible.
• Fargion (astro-ph/9710029) and Weiler
  (hep-ph/9710431) envisioned the following
  annihilation process

• The production rate is greatly enhanced by the
  possible relic neutrino clustering in the
  galactic halo or in our galaxy cluster.
• If this process occurs, the secondary products
  contribute more than 10 to the observed cosmic
  ray flux above 1019 eV (Yoshida et al.,
  hep-ph/98080324).
• This excess in the cosmic ray flux, as well as
  the correlation of the UHE neutrino and the
  secondaries directions could be observed by
  the Auger experiment.

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Conclusions

• Great progress has been made in observations of
  the Cosmic Microwave Background Radiation.
• The most recent measurements severely constrain
  the cosmological parameters and the cosmological
  models describing the Universe.
• CMBR, LSS and SCP strongly indicate that the
  density of the Universe is very close to the
  critical density and favor models based on the
  Inflationary Paradigm.
• Massive relic neutrinos can play an important
  role in understanding the nature of Dark Matter.
• Indirect observation of the Relic Neutrino
  Background may be possible in the near future.
• This is not The End, this is just The Beginning!

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