Transcript Astrophysical Constraints on Dark Matter

2nd Korea-China joint seminar on Dark Matter Search
Progress of dark matter research
Xuelei Chen
陳學雷
National Astronomical Observatory of China
Nov 24, 2007 Seoul National University
Outline
• A brief Review of DM problem
• Some Cosmological Constraints on
non-conventional DM
• Suggestion on searching for Light DM
Evidences of dark matter
Most Dark matter is not ordinary matter
(baryon)
BBN & CMB:
baryon is only 4-5%
Can neutrinos be the dark matter ?
at freeze-out
at freeze-out
if weakly interacting
hot dark matter relativistic
m< 1 keV
warm dark matter quasi-relativistic 1 keV < m < 10 keV
cold dark matter non-relativistic m > 10 keV
Pure HDM(light neutrino) is
excluded.
CDM, WDM, and mixtures are
possible.
Tegmark et al (SDSS),
astro-ph/0608632
Weakly Interacting Massive Particle
(WIMP)?
dark -- weakly interacting?
cold -- massive (non-relativisitic)
abundance @ early Universe
freeze out when H = n <Av>,
lightest supersymmetric particle
(neutralino, gravitino, sneutrino, ...?)
Kaluza-Klein particle?
Dark Matter or MOND?
Testing modified gravity: bullet cluster (Clowe et al astro-ph/0608407)
Improbable as it is, all other explanations are more
improbable still.
--Sherlock Holmes
Searching for DM:
WIMP direct search
• DM can penetrate shielded (underground) detectors
• detecting single atom collision:
elastic--phonons and heat
inelastic -- ionization/excitation
• identification/annual modulation
DAMA, CDMS, Edelweiss,
CRESST, KIMS, ZEPLIN,
XENON...
Indirect Search
Gamma-Ray from DM annihilation
High Energy Neutrino from DM annihilation
Cosmic Ray from DM annihilation
GLAST
Challenge to CDM:
halo profile
simulation (Navarro, Frenk,
white 1996): cusp
NFW96, rotation curve
• Is density profile really universal?
•What is the real slope
NFW: 1.0 Moore 1.5
• Observation
beam smearing? 21cm, H, CO
some agree w/ cusp, but most dwarf
has core (slope 0.2)
• Cusp cheat as core
vg != vc , because of inclination, effect of bulge and bar,
supported by pressure, star orbit in triaxial halo, ...
gas
Challenge to CDM:
halo substructure
Simulation indicates 102-3 DM subhalo
in Local Group, but observed satellites ~ 20
• satellites do exist, but star formation
suppressed (after reionization?)
• satellites orbit do not bring them to
close interaction with disk, so they will not
heat up the disk.
• Local Group dwarf velocity dispersion
underestimated
• halo substructure may be probed by
lensing (still controversial)
B. Moore et al 1997
Dwarf galaxies
Nearly 20 new dwarf galaxies
discovered
Updated Mateo plot
minimal mass of DM halo for
dwarf galaxies
5 x 107 Msun
Core and low phase space
density in dwarf galaxies
Gilmore et al 2007
But ...
Simon & Geha 2007
Missing satellite problem solved?
Simon & Geha 2007
Alternatives
Warm Dark Matter,
Self-Interacting Dark Matter
Strongly Interacting Massive Particle
Annihilating DM
Decaying DM
Fuzzy DM
Light DM
...
Test DM interaction
with CMB and LSS
XC, Hannestad, Scherrer 2002
Cosmic Ionization History: constraint
on DM decay/annihilation
z ~ 1000
z ~ 30
?
z~6
z~0
DM decay affects reionization
XC & Kamionkowski 2004
Constraint on DM decay
XC & Kamionkowski 2004
L. Zhang et al. 2007
Light (MeV) Dark Matter?
If dark matter mass is 1-100 MeV
instead of 100 GeV (neutralino), then
the number density is much higher.
Annihilation rate ~ n2 (Boehm, Hooper,
Silk 2003)
INTEGRAL observation of
GC 511 keV line: where does
the positron come from?
CMB Constraint on Light Dark Matter
homogenous annihilation
during recombination
Impact on reionization
L. Zhang et al. 2006
Presense of a new interaction?
• supersymmetric version of
SU(3) x SU(2) x U(1) x U(1)
• mU ~ MeV
• vector gauge coupling ~ 10-6
• U-boson coupling allow
greater DM annihilation rate,
leads to the correct abundance
P. Fayet astro-ph/0702176
U-boson mediated interaction
of MeV dark matter
Ek ~ MDM v2
• Cross section about 102 times WIMP (assume
mass ~ MW) interaction mediated by W
• Collision Rate ~ cross section/mass, about 106
times WIMP collision rate
A new possibility:
direct search of Light DM
• Light Dark Matter mass: 1-100 MeV
• interaction: weak interaction, or new
interaction (e.g. mediated by U-boson)
• Direct Search have so far been limited to
m>10 GeV
• Need develop technology to constrain this part
of parameter space
Nuclear Recoil
Pulse Approximation: nucleus
obtain a sudden speed
Elastic: The whole atom
moves, no excitation, energy
is dissipated as phonons
and/or heat
Inelastic: Some energy is
converted to ionization and/or
excitation.
Recoil Energy
very small
For each set of 5
curves, assume
detector nuclei of
mass 10, 20, 40, 80,
160 GeV
Recoil with Electron
DM scattering with electron:
Discussions
• Need to detect very small recoil energy: 1-10 eV
• Nuclear Recoil and Electron Recoil detect different
interaction
• Method of detection? Suggestions Welcome!
• What is the background?
Thanks!