Dark Matter

1
Dark Matter Dark EnergyNew Challenges for
Particle Physics

• Jim Siegrist
• UCB/LBNL
• USF, 29-Apr-04
• Acknowledgement Murayama, Hinchliffe, Quantum
  Universe Writing Team

2
What is the nature of the universe and what is it
made of?What are matter, energy, space and
time?How did we get here and where are we going?
Particle Physics and the Quantum Universe

• Understanding the Universe requires particle
  physics to determine its fundamental nature
• Astrophysical obs ? parameters of Universe
• Accelerator expts ? search for quantum
  explanation
• Two ends must meet
• Observing the relics of the big bang
• Recreating the particles and forces of early
  Universe at accelerators

3
Particle Physics Has a Complete Understanding of
Ordinary Matter

• We have a commanding knowledge of the particles
  and forces around us.
• A theoretical framework called the Standard
  Model (SM) describes data with exquisite
  precision.

4
Symmetry Plays the Central Role

• Formulation of the SM reveals that the laws of
  physics exist because of underlying (global, eg.
  space-time independent) symmetries
• Translation invariance gt momentum conservation
• Rotational invariance gt angular momentum
  conservation
• Some symmetries have been lost as the Universe
  has cooled from the Big Bang
• Particle masses arise because the vacuum today
  has different symmetry properties than during the
  initial fireball
• Space-time dependent (local, or gauge) symmetries
  generate the forces in the SM

The Standard Model Framework indicates how it can
be systematically extended
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Recent Discoveries IndicateParticle Physics Has
Reached a Singular Moment
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A Revolution in Particle Physics Some of the
Open Issues

• What is Dark Matter?
• What is Dark Energy?
• Are there extra space dimensions?
• Do all the forces become one?
• What happened to the anti-matter?
• How did the Universe come to be?

We know the Standard Modelis an incomplete
description of the Universe
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Dark Matter

• Astrophysical Perspective
• Particle Physics Perspective
• Models for new physics
• Current and future work

8
Astrophysical Perspective Galaxy Rotation
Curves

• Scale 10KPc (30,000 light years)
• Use Doppler shift of light from star in spiral
  galaxy to give velocity (red shift)
• Expect velocity to fall off with distance from
  center
• - but it doesnt

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Dark Matter in Galaxy Clusters

• Galaxies form clusters bound in a gravitational
  well
• Hydrogen gas in the well gets heated, emits
  X-rays
• Can determine baryon fraction of the cluster
• fBh3/20.056?0.014
• Combine with the BBN
• Wmatterh1/20.38?0.07
• Agrees with other methods

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Microlensing Searches

• Gravitational lensing effect

• Observed MACHO Event
• Symmetrical Light Curve and one off
• Gravitational identical curves at different
  wavelengths (unlike variable stars)

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Particle Physics Perspective

• Big Bang Nucleosynthesis tells us the Dark Matter
  cannot be baryonic
• We are forced to introduce something beyond the
  Standard Model framework.

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Particle Dark Matter

• It is not dim small stars (e.g., MACHOs)

• WIMP (Weakly Interacting Massive Particle)
  strongly favored
• Stable heavy particle produced in early Universe,
  left-over from near-complete annihilation
• TeV1012eV the correct mass scale

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Cold Thermal Relics
Figure from Kolb

• Dark Matter fraction increases as M increases
• Dark Matter fraction increases as ? decreases
• Interactions must be fully specified before a
  candidate can be ruled out. Calculations are
  therefore limited to those fully specified models.

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A Promising Model Supersymmetry(SUSY)

• Additional symmetries have to be proposed to
  extend the SM to solve the Dark Matter problem
• One approach is to double the particle spectrum
  by positing a symmetry that links fermions to
  bosonsgiving a sparticle paired with each SM
  particle, differing by ½ unit of spin
• Originally studied for other reasons

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Problems Possibly Solved by Supersymmetry

• Dark Matter problem the lightest SUSY particle
  is stable gt candidate for Dark Matter
• Explanation for how mass is generated in the SM
  gt requires a heavy top quark, as was observed
  after the SUSY prediction

• Introduces a higher level of symmetry that
  stabilizes the theory against higher order
  corrections (solves the hierarchy problem)
• Provides for Unification of the forces into a
  single force at very high energies
  (alternatively, at very short distances or in the
  very early Universe)

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Standard Model and Supersymmetry
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Breaking Supersymmetry
i.e. SM particles plus two Higgs doublets and
their SUSY partners

• How is supersymmetry broken?
• Supergravity-inspired (mSUGRA)the typical
  benchmark
• parameters m1/2, m0, A0, tan ?, sign(?)
• radiative EWSB occurs naturally from large top
  mass
• the ?01 is the LSP
• ?01, ?02, ??1, sleptons and h are light
• ?03, ?04, ??2, squarks and gluinos are heavy
• Many other possibilities have been studied

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Opening the Door

• Once SUSY is introduced,
• We can get started to discuss physics at shorter
  distances.
• It opens the door to the next level
• Hope to answer great questions
• The solution to the Dark Matter problem itself,
  e.g., SUSY, provides additional probe to how the
  Universe works.

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SUSY and Dark Matter

• Most SUSY models have unbroken R-parity that
  guarantees that lightest sparticle (LSP) is
  stable
• LSP must be neutral candidates are B W0 H ? and
  G
• ? is strongly disfavored by LEP and direct
  searches
• Parameters m1/2 (gaugino masses), m0 (squark
  masses), tan ?, sign(?), A, specified at GUT
  scale, fully describes model.
• LSP is usually B and mass controlled by m1/2

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SUGRA Allowed Regions
Plots are usually shown for fixed tan ß sign (µ),
A as a region in m1/2 m0 space.
Low mass region m1/2 and m0 are small
0.1 ? ?h2 ? 0.3
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After WMAP Results
Recall for LHC that roughly mg 2.4m1/2 and
me 1.1m0

LSP forced to lower masses by WMAP results good
for accelerator based searches.
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Current and Future Experimental Work

• Today Tevatron
• Soon Large Hadron Collider
• Tomorrow Linear Collider

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Tevatron
SUSY higgs A/H in ??, bb
Run II 5? discovery M175 GeV for tan?50 with 5
fb-1
bb (h/H/A) enhanced at large tan?A ? bb, so 4
bs in final state A ? ??, Run I analysis 4
jets, 3 b tags

• Work in progress
• Higgs multijet trigger studies
• 4 jets QCD background
• B-mistag studies for background

Control sample requires two b-tags Data and MC
agree very well
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Next Steps LHC in 2007
The LHC detectors are designed to find the SM
Higgs. Low mass is covered by ??, ttH(bb),
qqH(WW,??). A low mass Higgs has many
accessible decay modes ? some couplings measured.
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ATLAS Detector at CERNs Large Hadron Collider
Inner Tracking Detector
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ATLAS Overview

• Production is complete or in progress for most
  ATLAS components.
• Underground installation has been underway for
  some months.
• The schedule continues to be tight, but it is
  feasible for ATLAS to be ready for first LHC beam
  as planned in 2007.

http//atlas.web.cern.ch/Atlas/TCOORD/Activities/T
cOffice/Scheduling/Installation/UX15webcams.html
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LHCs Task

• Find the particle(s) responsible for mass
  generation.
• Could be Higgs, many Higgss, SUSY, Extra
  dimensions
• Power of LHC is its enormous mass reach relative
  to current facilities.
• Even low luminosity will open a new window.
• 10pb -1 (1 day at 1/100 of design luminosity)
  gives 8000 t?t and 100 QCD jets beyond the
  kinematic limit of the Tevatron
• If SUSY is correct, it could be found with 100pb
  1

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How fast can SUSY be found at LHC?
The LHC should be able to establish the existence
of SUSY and open many avenues to study masses and
decays of SUSY partices, if m(SUSY) is less than
a few TeV. For example in the SUGRA model, the
cosmologically interesting region of the SUSY
search will be covered in the first weeks of LHC
running, and the 1.5 to 2 TeV mass range for
squarks and gluons will be covered within one
year at low luminosity.
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The Linear Collider

• Full exploration of SUSY requires the CERN LHC
• A proton-proton collider with an energy seven
  times that of the Tevatron.
• Together with a high-energy ee- linear collider.
• The LHC and a linear collider are both necessary
  to discover and understand the new physics at the
  TeV scale.
• A coherent approach, exploiting the strengths of
  both machines, will maximize the scientific
  contributions of each.

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Why Both a Hadron and Electron Collider?Precision
Data
The present precision data were collected at
hadron and electron machines. The two probes
provide complementary views much like infrared
and ultraviolet astronomy complement the optical.
We fully expect this theme to continue into the
future.
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How Will a 500 GeV Linear Collider Complement the
LHC?

• Experiments at the LHC are likely to discover
  Dark Matter
• But a linear collider answers crucial questions
• What is the spin state of the candidate?
• Does it have the coupling consistent with Dark
  Matter particles?
• Is it produced in a manner consistent with
  production of relics in the early Universe?

A fully International Project planned for the
next decade
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Dark Energy

• Astrophysical Perspective
• Particle Physics Perspective
• Models and Ideas
• Current and Future Work (for Supernovae)

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Type-IA Supernovae
As bright as the host galaxy
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Type-IA Supernovae

• Type-IA Supernovae standard candles
• Brightness not quite standard, but correlated
  with the duration of the brightness curve
• Apparent brightness
• ? how far (time)
• Know redshift
• ? expansion since then

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What makes the supernova measurment special?
An exhaustive accounting of sources of SN
systematic uncertainities

• SN Ia Evolution
• shifting distribution of progenitor
  mass/metallicity/C-O
• shifting distribution of SN physics params
• amount of Nickel fused in explosion
• distribution of Nickel
• kinetic energy of explosion
• opacity of atmospheres inner layers
• metallicity
• Gravitational Lensing (de)amplification

• Dust/Extinction
• dust that reddens
• evolving gray dust
• clumpy
• homogeneous
• Galactic extinction model
• Observational biases
• Malmquist bias differences
• non-SN Ia contamination
• K-correction uncertainty
• color zero-point calibration

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Type-IA Supernovae

• Clear indication for cosmological constant
• Can in principle be something else with negative
  pressure
• With wp/r,
• Generically called Dark Energy

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Cosmic Concordance

• CMBR flat Universe
• W1
• Cluster data etc
• Wmatter0.3
• SNIA
• (WL2Wmatter)0.1
• Good concordance among three

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Constraint on Dark Energy

• Dark Energy is an energy that doesnt thin much
  as the Universe expands!

• Need negative pressure
• Data consistent with cosmological constant
  wp/r1

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Cosmic Coincidence Problem

• Why do we see matter and cosmological constant
  almost equal in amount?
• Why Now problem
• Actually a triple coincidence problem including
  the radiation
• If there is a fundamental reason for
  rL((TeV)2/MPl)4, coincidence natural

Arkani-Hamed, Hall, Kolda, HM
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Embarrassment with Dark Energy for Particle
Physics

• A naïve estimate of the cosmological constant in
  Quantum Field Theory rLMPl410120 times
  observation
• The worst prediction in theoretical physics!
• People had argued that there must be some
  mechanism to set it zero
• But now it seems finite???

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Many ad-hoc Models to Explain Dark Energy
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Current and Future Work

• Nearby Supernova Factory/ SCP
• SNAP
• Some thoughts

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Understanding Supernovae
Nearby Supernova Factory well in progress,
refining understanding Supernova Cosmology
Project 2003 Results Higher redshifts,
Greatly improved systematics checks Ground
based searches continuing Refining
understanding (cf. CMAGIC ?m0.08) Probing
averaged DE equation of state w Important,
but will reach ground systematics limit
--cant achieve robust w? --confusion limit
in interpreting nature of DE
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Nearby SN Factory follow-up Instrument
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SNAP/JDEM The Next Generation

• Supernova/Acceleration Probe
• Dedicated exploration of dark energy w(z)
• Maps expansion history a(t)
• Reveals dark matter thru gravitational lensing

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SNAP/JDEM The Next Generation

• SNAP is wide, deep, and colorful
• Essential to control systematics
• Realized by LBNL technology CCDs

SNAP focal plane array
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SNAP Fundamental Physics

• Space allows high z and systematics control
• w(z) ? V / V(?)
• High energy physics, extra dimensions, new
  gravity, inflation redux?

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How can we solve the mystery of dark energy?

• A Dark Energy fills the vacuum of empty space
• Accelerating expansion of Universe
• Dark energy needs a quantum explanation
• The Higgs field fills the vacuum of empty space
• Gives particles mass
• Are dark energy and the Higgs related?
• SUSY a natural context for both

LHC, SNAP/JDEM and LC are crucial tools for
discovery
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Cosmology and Particle Physicsmeet at TeV scale

• Dark Matter
• Fermi (Higgs) scale
• v250GeV
• Dark Energy
• rL(2meV)4 vs (TeV)2/MPl0.5meV
• Neutrino
• (Dm2LMA)1/27meV vs (TeV)2/MPl0.5meV
• TeV-scale physics will be rich

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Conclusions

• Answers to origins of Dark Matter and Dark Energy
  soon
• Many exciting possibilities
• One of several thrusts in particle physics today

Expect a 21st Century Revolution in Particle
Physics
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References

• Books
• The Elegant Universe, B. Greene, Random House,
  1999.
• Supersymmetry, G. Kane, Perseus Publishing, 2000
• Quarks, Leptons and the Big Bang, J. Allday, IOP,
  2002.
• Facts and Mysteries in Particle Physics, M.
  Veltman, World Scientific, 2003.
• The Fabric of the Cosmos, B. Greene, Knopf, 2004.
• Connecting Quarks with the Cosmos, National
  Academy Press, 2003
• Articles
• Papers in the Scientific American special report
  on the cosmos (February 2004)
• The Cosmic Symphony, Wayne Hu and Martin White
  (p. 44)
• Reading the Blueprints of Creation, Michael A.
  Strauss (p.54)
• From Slowdown to Speedup, Adam Riess and
  Michael S. Turner (p. 62)
• Out of the Darkness, George Dvali (p. 68)
• Web sites
• http//www.ostp.gov/ (see OSTP NEWS, Physics of
  the Universe Report)
• http//www.interactions.org
• http//www.interactions.org/pdf/Quantum_Universe.p
  df
• Experiments
• ATLAS http//atlas.web.cern.ch/Atlas/Welcome.html
  

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