Fundamental Physics from Space

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Fundamental Physics from Space

• Standard Model
• What it Explains
• What it doesnt Explain

Scott Dodelson University of Kentucky March 9,
2006
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Standard Model of Particle Physics
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Standard Model of Particle Physics

• 4 Gauge fields associated with SU(2)xU(1)
• One left-handed doublet (eL,?L)
• One right-handed singlet eR
• One scalar (Higgs) field

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Three minor extensions (all of which won Nobel
Prizes)

• Quarks as well as leptons
• ? Quantum Chromodynamics gluons and their
  interactions
• ? Three generations electron, muon, tau (and
  similarly for quarks)

Gravity (General Relativity)
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This Model enables us to compute the constituents
of the universe

• Primordial Production of Light Elements
• Existence and blackbody nature of Cosmic
  Microwave Background

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SM allows computation of light element abundances
n?p conversions stop because weak interactions
freeze out
Neutrons Boltzmann suppressed difference because
of mass (QCD)
Neutrons decay (weak interaction)
Light nuclei form (EM)
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Predictions depend only on baryon density

• Unknown parameter ?B ?B/?cr
• Deuterium measurements most accurate ?B 0.04
• Agrees with WMAP results
• Possible conflict with He or Li

Coc et al. 2004
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EM predicts that cosmic photons have blackbody
shape

• Tightly coupled to free electrons early on via
  Compton scattering
• Electrons protons combine to form neutral H at
  kT0.3 eV (EM)
• Photons travel freely thereafter, but maintain
  thermal shape

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Its not just Cosmology
All phenomena observed at the largest
accelerators in the world can be explained by the
Standard Model
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Its not just Particle Physics
Politics Sociology Psychology Biology Chemistry At
omic Physics Nuclear Physics Particle Physics

• In the pyramid of knowledge, The Standard Model
  is the base and, in principle, can explain all
  phenomena.

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Except

• Neutrino Transformations
• Gravitational Potential Wells
• Type Ia Supernovae Brightness
• Acoustic Oscillations in CMB

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Neutrinos change flavor as they propagate over
long distances
Many fewer electron neutrinos from Sun than
expected
Bahcall
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What is the probability that an electron neutrino
will transform into a muon neutrino?
Evolve the initial state with the Hamiltonian
The neutrino term in Weinbergs Hamiltonian (Z??)
does not mix ?e and ?? that part of H is
diagonal
In the absence of any other terms (e.g. mass
terms)there will be no transformations from one
flavor to another
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Mass terms mix flavors
There is a mass matrix with masses me and m? and
mixing angle ? (similar to CKM matrix of quarks).
Take the inner product with the state (0 , 1) and
squareto get transformation probability
In the high energy limit,
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Electron Neutrino Constraints
Solar
Solar Kamland
Astrophysical evidence for ??-?? transitions ?m2
0.005 eV2
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Two mechanisms for sub-eV masses
mR0 One Dirac neutrino with mass mLR ltlt other
masses

• mR mLR One light Majorana neutrino with mass
  mLR 2/mR

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Potential Wells are much deeper than can be
explained with visible matter
We have measured this for many years on galactic
scales
Kepler vGM/R1/2
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Simplest Explanation is Dark Matter
Without dark matter, potential wells would be
much shallower, and the universe would be much
less clumpy
Clumpiness
?Large Scales
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Most robust constraints on non-baryonic dark
matter from clumpiness in Universe
There is 7 times more non-baryonic (non-normal!)
matter in the Universe than baryonic matter.
SDSS Tegmark, et al. 2005
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Where is dark matter found in Weinbergs
Lagrangian?

• Cannot interact with photons (neutral)
• Must be non-relativistic when structure
  formation began (MgtkeV)
• Must be stable
• Likely weakly interacting

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Supersymmetry Add partners to each particle in
Weinbergs Lagrangian
Beautiful theoretical idea invented long before
it was realized that neutral, stable, massive,
weakly interacting particles are needed
Neutralinos
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Distant Type Ia Supernovae are fainter than they
would be if the universe were decelerating
Accelerating
Decelerating
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Expansion Scale factor a grows with time
Acceleration da/dt grows with time
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Acceleration is surprising
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To get acceleration in the context of general
relativity
Need substance whose energy density remains
roughly constant as the universe expands
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Constant Energy Density is Surprising
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Where is Dark Energy found in Weinbergs
Lagrangian?

• Can add scalar field
• It behaves like NR matter unless mlt10-33 eV

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Mystery has broad appeal
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Acoustic Oscillations in the Cosmic Microwave
Background
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The power spectrum shows well-defined peaks and
cross-correlation with polarization
These striking features are best explained by an
early epoch of acceleration (inflation) which
requires field with negative pressure
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We see photons today from last scattering surface
when the universe was just 400,000 years old
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Oscillations can be decomposed into Fourier modes


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Combine Fourier Modes to Produce Structure in our
Universe




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In this simple example, all modes have have
wavelength/frequency
More generally, at each wavelength/frequency,
need to average over many modes to get spectrum
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What spectrum is produced by a piano string
Middle C on a piano
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Compare the piano spectrum to CMB spectrum
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CMB is different because

• Fourier Transform of spatial, not temporal,
  signal
• Time scale much longer (400,000 yrs vs. 1/260
  sec)
• No finite length all k allowed!

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Largest Wavelength/Smallest Frequency
Smallest Wavelength/Largest Frequency
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Acoustic Oscillations

• Pressure of radiation acts against clumping
• If a region gets overdense, pressure acts to
  reduce the density restoring force
• Oscillation frequency largest for small
  wavelength modes

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Why peaks and troughs?

• Vibrating String Characteristic frequencies
  because ends are tied down
• Temperature in the Universe Small scale modes
  begin oscillating earlier than large scale modes

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Puzzle Why are all modes in phase?
The perturbation corresponding to each mode can
either have zero initial velocity or zero initial
amplitude
We implicitly assumed that every mode started
with zero velocity.
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Remember that at anywavelength, we are averaging
over many modes with different direction.
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If they do all start out with the same phase
First peak will be well-defined
Clumpiness
Time/(400,000 yrs)
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As will first trough ...
And all subsequent peaks and troughs
Clumpiness
Time/(400,000 yrs)
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If all modes are not synchronized though
First Trough
First Peak
Clumpiness
Clumpiness
Time/(400,000 yrs)
Time/(400,000 yrs)
We will NOT get series of peaks and troughs!
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Solution Period of Early Acceleration
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During Inflation, quantum mechanical fluctuations
slightly distort smooth universe
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Inflation gives a beautiful explanation of
synchronization
When modes leave the horizon, they cease to
evolve when they re-enter, only the constant
mode remains
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To get inflation, need early dark energy!

• Different than current dark energy about 40
  orders of magnitude denser.
• One similarity no connection to anything in
  Standard Model

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Conclusions

• Standard Model has taught us how to do cosmolgy
• Space-observations offer the only evidence for
  physics beyond SM
• Profound mysteries remain to be solved neutrino
  mass, dark matter, dark energy

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