暗黒物質対消滅起源のガンマ線

暗黒物質対消滅起源のガンマ線
久野純治 (東京大学宇宙線研究所）
研究会「CANGAROO望遠鏡によるガンマ線天文学の新展開」
日時：２００３年１２月１１日（木）-１２日（金）
場所：京都大学基礎物理学研究所湯川記念館3F 大講演室
1, Introduction
Evidence of cold dark matter
Fit to the WMAP , CBI, ACBAR,
2dFGRS and Lyman α forest data
2dFGRS v.s. N-body simulation for
Large-scale structure formation
What is this dark matter?
Candidate of dark matter
MACHO (almost excluded)
107.5 M  M  30M Microlensing
Wide binaries (Chaname et al)
45M  M
Neutrino (Not cold)
It might be hot dark matter, thus
  0.01 ( m  1eV )
Unknown stable particle
Relics in the early hot universe.
WIMP (Weakly interacting massive particle) (Cold)
SUSY particle, Kaluza-Klein particle, Wimpzilla,,,
Axion (Cold)
SUSY dark matter
Solves hierarchy problem
SUSY GUTs
Light Higgs boson
Lightest SUSY particle(LSP) is
stable due to R parity.
SM particles; even, SUSY particles; odd
→ Dark Matter
Nature of LSP
It depends on the SUSY breaking mechanism
0
0
0
0
0
Neutralino ( 10 ); 1  a1B  a2W3  a3 H1  a4 H2
0
0
(
H
(
B
)
Bino
-like or Higgsino ) -like in supergravity
0
(
W
Wino 3 )-like in the anomaly mediation
Gravitino (G0 ) in the gauge mediation
Direct search for DM ｂｙ the nucleus elastic scattering
Dirac neutrino (sneutrino) mass > 100TEV
Dark matter should be Majorana fermion or real scalar
if it has weak charge.
DM genesis
Thermal abundance
10 10  SM particles is blocked when
T  1/ 20 m 0 .
1
0
1
10 (56)
(1/100GeV ) 2
v annihiration
eff
Smaller DM ( 0.27) may mean
larger annihilation rate.
Notice co-annihilation may
enhances cross section when
SUSY particles masses are degenerate.
10 1  SM particles, 10  SM particles,
(Nath et al)
Non-thermal production
DM is produced after T  1/ 20 m 0 by non-thermal
1
process.
(for example, G, Qball,  10  )
 0
1
 1/ 20
10 (56) 
 T / m 0

1
 (1/100GeV )2

 v annihiration eff

In this case, the larger annihilation rate, such as in
Higgsino-like or Wino-like case, is favored.
Detection of DM
Direct detection by elastic scattering with nucleus.
 N  N
0
1
0
1
DAMA, EDELWEISS, CDMS, Zeplin, ……
Indirect detection of neutrinos, antiproton, positron,
and gamma ray from DM annihilation in our Galaxy,
Sun, or Eearh.
10 10  p, e , , 
Collider experiment
LHC starts on 07’.
It determine mass and properties of the DM
candidate.
2, Dark matter distribution
N-body simulation provides
universal cuspy profile for the
halo DM density distributon
(Navarro, Frenk & White,
96,97).
 NFW (r ) 
0
(r / r0 )(1  r / r0 ) 2
Navarro, Frenk &White
 M 99 (r ) 
0
(r / r0 )1.5 (1   r / r0  )
1.5
Moore
High resolution N body simulation
Large N and small time stepsize are required.
( N O(10)M )
Recent simulation observed
deviation from the universal
profile for r  0.01 rV .
Time evolution
(Figures;Fukushige and Makino)
Cusp/Core problem
Rotation curve measure ment of Low Surfacebrightness Galaxies by HI and Halpha.
Data prefer soft cores .
Early suspicion on observation;
beaming, pointing error,
small sample, inconsistency
among observations, etc.
de Blok(2003): These problems
no more exit.
Measurement of gravitational
lense constrains DM profile
for clusters.
Sand et al show   0.54
Objection :Ellipticity (Dalal et
al)
A little good news.
1/ r 3 for large radius is favored.
(CL0024+11654, Kneib et al)
Our galaxy
Our galaxy is High surface-brightness galaxy.
(Baryon rich, Bar, BH )
It is difficult to say something, especially DM
profile around the galactic center.
http://www.astronomynotes.com/ismnotes/rotcurv2-big.gif
3, Gamma ray from DM annihilation
in Galactic center
Gamma ray from DM annihilation
line spectrum: 10 10   ,  Z 0
continuum spectrum: 10 10  W W  , Z 0 Z 0 ,
 0 
Merit and Demerit
Merit:
Characteristic spectrum, e.g. line.
Sensitive to heavier DM
Demerit: Cross section depends on DM proparties.
Sensitive to DM halo profile.
Gamma ray flux
d  ( E )
dE
 9.3 1012 cm-2sec-1GeV -1  J 
 100GeV 


 m 0 

1

2
v VV ' 
dNVV ' 
 27 3 -1 

cm sec 
VV ' dE  10
where
 DM
1


dl 
d 
J  
-3 

sight
lineof
8.5kpc 
 0.3GeVcm 
2
Galactic Halo profile
Dependence on DM profile is huge.
 DM
1


J  
d 
dl 
-3 

lineof
sight
8.5kpc 
 0.3GeVcm 
 M 99 (r ) 
0
(r / r0 )1.5 (1   r / r0  )
 NFW (r ) 
1.5
0
(r / r0 )(1  r / r0 ) 2
modifed (r ) 
isothermal
0
(1   r / r0  )
2
2
J  105
J  103
J  3 101
for R0  8.5kpc,  DM ( R0 )  0.3GeVcm-3 and   103.
In the following, I take the moderate value, that is
J  103 .
DM annihilation cross section
Annihilation cross section to fermions is suppressed
by the fermion mass due to the S wave annihilation.
Sizable cross section to continum gammais expected
when m  mW .
0
1
Cross section depends on propaties of the DM.
Case 1:Bino-like DM.
Interaction is very weak.
MSUGRA + thermal production favor this.
Case 2: Higgsino or Wino DM.
These have SU(2) weak charge.
Bino-like DM
Line spectrum.
4
 100GeV   J  
12
-2
-1
  2.0 10 cm sec  
  3
3 
 m
10

10

l

 
Sensitive to slepton mass.
Continuum spectrum
MSUGRA simulation by
Feng et al.
m 0  61,97,120, 202GeV.
1
 v 
2
m
 10
cW2 ml4
2
Higgsino or Wino DM
They have SU(2) weak charge and acompany
with

SU(2) partner, those are chargino,  . When they
are heavier than W boson mass, the masses are
degenerate.
Annihiration cross section to 2 gamma’s is
independent of the DM mass at the leading order.
 v 
2
 1   1
4  2
For Wino (Higgsino)
2
 4  sW mW
This means that line gamma search is sensitive to
heavier DM.
4
However, this behavior is strange since  v   2 .
vm 0
1
Non-relativistic effects
DM is highly non-relativistic (v / c  103 ). Thus, the cross
section is sensitive to existence of bound state under
Yukawa potential induced by W exchange.
 v (cm3 sec1 )
for  0  0  2
v / c  103
 m  0.1 GeV
 m  1 GeV
Wino-like
Higgsino-like
Leading order cal.
E  mv2 / 2  0
Zero energy resonance
enhances the cross section.
Bound state
W-exchanged
Yukawa potential
Line spectrum (

 m  0.1GeV
 m  1GeV
Wino-like
Flux (cm-2sec-1 )   103
103

 m  0.1GeV
 m  1GeV
Higgsino-like
).
Photon energy (GeV)
Continuum spectrum (  m  0.1GeV ,
Flux (cm2 sec1 GeV 1 )
Wino-like
17
10
1011
9
10
  103
)
Flux (cm2 sec1 GeV 1 )
Higgsino-like
1019
1015
1017
1013
1015
1013
1011
The shaded regions correspond to S> BG.
d B.G. / dE  9.1105  (E /1GeV)2.7  (EGLET)
There are already some regions constrained by the EGRET.
EGLET
Gamma ray spectrum from
Galactic center observed by
EGLET is not well fit to the
standard explanation of diffused
gamma,
p, He  X 
  0  2 (index=2.72)
It might come from DM annihilation.
(Cesarini et al)
4, Summary
After WMAP measurement, DM search is very
important subject. Gamma from DM annihilation is
sensitive to relatively heavier DM, and it has
different dependence from other DM searches.
Will gamma from DM annihilation at Galactic center
be observed or not ? Or, can we discriminate
particle physics models or astronomical models? At
present, it is hard to answer them, because gamma
ray signal depend on detail of both models.
If DM candidate is discovered at new collider
(LHC?) or DM-like gamma ray is observed, DM
astronomy will be started.

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