M. Ma pe lli
SISSA
Deca ying Cold a nd Wa rm Da rk Ma tter:
re ioniza tion a nd the rma l history
of the unive rse
colla bora tors
A. Ferra ra , E. Pierpa oli
Cold a nd Wa rm Da rk Ma tter:
MAIN DIFFERENCE:
WDM pa rticles, less ma ssive, have higher
DISPERSION VELOCITY tha n CDM particles.
WDM particles can prevent the forma tion of the
smallest halos, a lleviating the “substructure crisis” of
CDM models; but they delay (maybe too much) the
structure forma tion (Ostriker & Steinha rdt 2003)
Current observa tions cannot rule out the
CDM or the WDM scenario
How to distinguish among DM models ?
DM DECAYs/ ANNIHILATIONs
e+ + e-
dm
(Hooper & Wa ng 2004)
e+ + e-
dm + dm*
F+, Z'
(Asca siba r et a l. 2005)
And the obse rva tions?
INTEGRAL map of the 511 kev emission from the
Galactic center
Bulge excess flux:
~ 10- 3 ph cm - 2 s- 1
Knodlseder et a l 2005
And the obse rva tions?
The ore tic a l e xpla na tions:
SN IA (Knolse de r e t a l. 2005)
de c aying/ a nnihila ting da rk
ma tte r (Boehm et al. 2004; Hooper &
Wang 2004; Ascasibar et a l. 2005) -->
LIGHT DARK MATTER (1-100 MeV)
DM de c a ys in the e a rly unive rse :
DM decays/ a nnihilations ca n be detected not only as a
emission line in the local universe, but also as a
background due to particles decaying at different z
I derive the COMOVING DECAYING RATE
a nd
I use it to calculate the IONIZATION and the HEATING
of the universe from the last sca ttering surfa ce due to
DM deca ys
Are the deca ying DM particles able to REIONIZE
the Universe achieving the e = 0.17 (WMAP) ?
DM de c a ys in the e a rly unive rse :
comoving deca ying ra te
energy injection rate per ba ryon
DM de c a ys in the e a rly unive rse :
of the energy goes into ionizations
of the energy goes into heating
(Chen & Ka mionkowski 2004; Shull & Va n
Steenberg 1985)
va riation of the ioniza tion
fraction (H)
va ria tion of the ioniza tion
fraction (He)
va ria tion of the matter
temperature
DM de c a ys in the e a rly unive rse :
We implement these equations into the public code
RECFAST (Sea ger, Sasselov & Scott 1999; 2000)
which calcula tes
ioniza tions,
recombinations a nd
matter tempera ture
evolution of the
relic fra ction of
electrons:
DM de c a ys in the e a rly unive rse :
Wha t kind of particles do we consider?
CDM:
LIGHT DARK
MATTER (LDM)
~1-100 Me V
gra vitinos
~10-100 Me V
WDM:
STERILE NEUTRINOS
~ 2-8 ke V
ne utra linos
> 30 Ge V
CDM:
LIGHT DARK MATTER (LDM)
Mass = 1-100 MeV, but probably << 30 MeV not to
overproduce the breemsstralung radiation from the
Galactic center (Casse' & Fayet 2005)
Can decay
Main candidate for the 511 keV emission from the
Galactic center both via decay (Hooper & Wang 2004)
and annihilation (Boehm et al. 2004; Ascasibar et al. 2005)
(Hooper & Wang 2004)
CDM:
LIGHT DARK MATTER (LDM)
T a factor 100
higher at z~10 !!!
τ ~ 0.01 << 0.17 (WMAP)
x increases already at z~100
Mapelli, Ferrara & Pierpaoli, in prep.
CDM:
GRAVITINOS
Mass = 10-100 MeV
They can decay; but, to remain good DM candidates,
their lifetime must be very long:
They cannot account for the 511 keV
CDM:
GRAVITINOS
NEGLIGIBLE !!!!!!
Mapelli, Ferrara & Pierpaoli, in prep.
CDM:
NEUTRALINOS
Mass >~ 30 GeV (Lightest Supersymmetric Particle)
They cannot decay remaining a good DM candidate,
because they are too massive
They can only ANNIHILATE
annihilation cross-section:
depends on z
rough approximation:
(Padmanabhan & Finkbeiner 2005)
CDM:
NEUTRALINOS
NEGLIGIBLE, unless we
a dopt a huge crosssection
Mapelli, Ferrara & Pierpaoli, in prep.
WDM:
STERILE NEUTRINOS
Most promising WDM candidate (Colombi et a l. 1996; SommerLa rsen & Dolgov 2001)
What are sterile neutrinos? MASSIVE NON-INTERACTING
neutrinos (=which do not partake the WEAK FORCE)
Predicted by the standard oscillation theory. They are
massive --> they can decay, following different channels
(Dolgov 2002)
Most important decay channel: RADIATIVE decay
Mass >= 2 keV from the analysis of the matter power
spectrum (Viel et al. 2005)
WDM:
STERILE NEUTRINOS
UPPER LIMIT ON THE MASS of sterile neutrinos by imposing tha t the
contribution of photons emitted by sterile neutrinos does not exceed the
observed unresolved HARD X-RAY BACKGROUND:
Tota l observed X-ra y
ba ckground
Unresolved X-ra y
ba ckground
(Bauer et a l. 2004)
m<10 keV
Mapelli & Ferrara 2005
WDM:
STERILE NEUTRINOS
UPPER LIMIT ON THE MASS of sterile neutrinos by the compa rison
with the X-ray line emission from the VIRGO cluster:
m < 8 keV
Abazajian, submitted
WDM:
STERILE NEUTRINOS
2 keV<= Mass <= 8 keV
Lifetime:
WDM:
STERILE NEUTRINOS
T a factor 100
higher at z~10 !!!
τ ~ 0.002 << 0.17 (WMAP)
x increases already at z~100
SIMILAR TO LDM !
Mapelli, Ferrara & Pierpaoli, in prep.
CDM/ WDM:
EFFECTS on the CMB spe c tra :
DM decays (especially LDM and sterile neutrinos) change
the ionization history and the temperature of matter
They can affect also the CMB spectra.
Are these effects detectable???
We implemented our modified version of RECFAST into the
public code CMBFAST (Seljak & Zaldarriaga 1996),
which calculates the TT, TE and EE spectra of the CMB
CDM/ WDM:
EFFECTS on the CMB spe c tra :
open circles: WMAP da ta
thick lines: with sudden
reioniza tion a t z~17 (WMAP)
TT
thin lines: without sudden
reioniza tion a t z~17
EE
bla ck lines: without
deca ying pa rticles
red lines: with deca ying
pa rticles (LDM)
TE
NEGLIGIBLE EFFECTS
on the CMB spectra
Mapelli, Ferrara & Pierpaoli, in prep.
CDM:
MORE EXOTIC DM mode ls
In the previous models we a ssume tha t the DM is composed
by one single species of pa rticles.
Different models suggest the existence of va rious species of DM.
For exa mple, Ka wa sa ki & Ya na gida (2005) expla in the 511 keV
emission from the Ga la ctic bulge postula ting a
deca ying SCALAR BOSON (1-10 MeV)
which contributes only to a sma ll fra ction of the DM:
CDM:
MORE EXOTIC DM mode ls
deca ying SCALAR BOSON (1-10 MeV)
SIMILAR TO LDM
and sterile
neutrinos
SUMMARY:
For LIGHT particles (LDM, sterile neutrinos) the contribution to
reionization and heating is important; whereas for heavy particles
(gravitinos, neutralinos) is negligible
LIGHT particles are sources of partial early ionization (in
agreement with models of complex reionization history: Cen
2002; Furlanetto & Loeb 2004)
Thomson optical depth <= 0.01, lower than WMAP but nonnegligible
Effect on the CMB spectra negligible
FUTURE:
The effect on the MATTER TEMPERATURE is relevant !!!!
Do decaying particles leave an imprint on the 21 cm maps
detectable with LOFAR, PAST, etc ?
(Valdes, Mapelli & Ferrara, in prep.)
Can an early reionization and an early heating modify the
structure formation history?
(Shchekinov & Vasiliev 2004)