40 research outputs found
Constraints on the parity-violating couplings of a new gauge boson
High-energy particle physics experiments allow for the possible existence of
a new light, very weakly coupled, neutral gauge boson (the U boson). This one
permits for light (spin-1/2 or spin-0) particles to be acceptable Dark Matter
candidates, by inducing sufficient (stronger than weak) annihilation cross
sections into e+e-. They could be responsible for the bright 511 keV gamma ray
line observed by INTEGRAL from the galactic bulge.
Such a new interaction may have important consequences, especially at lower
energies. Parity-violation atomic-physics experiments provide strong
constraints on such a U boson, if its couplings to quarks and electrons violate
parity. With the constraints coming from an unobserved axionlike behaviour of
this particle, they privilegiate a pure vector coupling of the U boson to
quarks and leptons, unless the corresponding symmetry is broken sufficiently
above the electroweak scale.Comment: 6 page
Ruling out the light weakly interacting massive particle explanation of the Galactic 511 keV line
Clarifying the covariant formalism for the SZ effect due to relativistic non-thermal electrons
We derive the covariant formalism associated with the relativistic
Sunyaev-Zel'dovich effect due to a non-thermal population of high energy
electrons in clusters of galaxies. More precisely, we show that the formalism
proposed by Wright in 1979, based on an empirical approach (and widely used in
the literature) to compute the inverse Compton scattering of a population of
relativistic electrons on CMB photons, can actually be re-interpreted as a
Boltzmann-like equation, in the single scattering approximation.Comment: 12 pages. Error in the interpretation of E. Wright's earlier results
corrected. Accepted for publication in PR
PAMELA and FERMI-LAT limits on the neutralino-chargino mass degeneracy
Searches for Dark Matter (DM) particles with indirect detection techniques
have reached important milestones with the precise measurements of the
anti-proton and gamma-ray spectra, notably by the PAMELA and FERMI-LAT
experiments. While the gamma-ray results have been used to test the thermal
Dark Matter hypothesis and constrain the Dark Matter annihilation cross section
into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA
experiment remains relatively unexploited. Here we show that the latter can be
used to set a constraint on the neutralino-chargino mass difference. To
illustrate our point we use a Supersymmetric model in which the gauginos are
light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP)
is the neutralino. In this framework the W^+ W^- production is expected to be
significant, thus leading to large anti-proton and gamma-ray fluxes. After
determining a generic limit on the Dark Matter pair annihilation cross section
into W^+ W^- from the anti-proton data only, we show that one can constrain
scenarios in which the neutralino-chargino mass difference is as large as ~ 20
GeV for a mixed neutralino (and intermediate choices of the anti-proton
propagation scheme). This result is consistent with the limit obtained by using
the FERMI-LAT data. As a result, we can safely rule out the pure wino
neutralino hypothesis if it is lighter than 450 GeV and constitutes all the
Dark Matter.Comment: 22page
Light neutralino dark matter in the MSSM and its implication for LHC searches for staus
It was shown in a previous study that a lightest neutralino with mass below
30 GeV was severely constrained in the minimal supersymmetric standard model
(MSSM), unless it annihilates via a light stau and thus yields the observed
dark matter abundance. In such a scenario, while the stau is the
next-to-lightest supersymmetric particle (NLSP), the charginos and the other
neutralinos as well as sleptons of the first two families are also likely to be
not too far above the mass bounds laid down by the Large Electron Positron
(LEP) collider. As the branching ratios of decays of the charginos and the
next-to-lightest neutralino into staus are rather large, one expects
significant rates of tau-rich final states in such a case. With this in view,
we investigate the same-sign ditau and tri-tau signals of this scenario at the
Large Hadron Collider (LHC) for two MSSM benchmark points corresponding to
light neutralino dark matter. The associated signal rates for these channels
are computed, for the centre-of-mass energy of 14 TeV. We find that both
channels lead to appreciable rates if the squarks and the gluino are not too
far above a TeV, thus allowing to probe scenarios with light neutralinos in the
14 TeV LHC run with 10-100 fb^{-1}.Comment: 19p, 4 Fig
Ruling out the light weakly interacting massive particle explanation of the Galactic 511 keV line
Kination Dominated Reheating and Cold Dark Matter Abundance
We consider the decay of a massive particle under the complete or partial
domination of the kinetic energy density generated by a quintessential
exponential model and we impose a number of observational constraints
originating from nucleosynthesis, the present acceleration of the universe and
the dark-energy-density parameter. We show that the presence of kination causes
a prolonged period during which the temperature is frozen to a plateau value,
much lower than the maximal temperature achieved during the process of
reheating in the absence of kination. The decoupling of a cold dark matter
particle during this period is analyzed, its relic density is calculated both
numerically and semi-analytically and the results are compared with each other.
Using plausible values (from the viewpoint of particle models) for the mass and
the thermal averaged cross section times the velocity of the cold relic, we
investigate scenaria of equilibrium or non-equilibrium production. In both
cases, acceptable results for the cold dark matter abundance can be obtained,
by constraining the initial energy density of the decaying particle, its decay
width, its mass and the averaged number of the produced cold relics. The
required plateau value of the temperature is, in most cases, lower than about
40 GeVComment: Final versio