1,114 research outputs found
Light spin-1/2 or spin-0 Dark Matter particles
We recall and precise how light spin-0 particles could be acceptable Dark
Matter candidates, and extend this analysis to spin-1/2 particles. We evaluate
the (rather large) annihilation cross sections required, and show how they may
be induced by a new light neutral spin-1 boson U. If this one is vectorially
coupled to matter particles, the (spin-1/2 or spin-0) Dark Matter annihilation
cross section into e+e- automatically includes a v_dm^2 suppression factor at
threshold, as desirable to avoid an excessive production of gamma rays from
residual Dark Matter annihilations. We also relate Dark Matter annihilations
with production cross sections in e+e- scatterings. Annihilation cross sections
of spin-1/2 and spin-0 Dark Matter particles are given by exactly the same
expressions. Just as for spin-0, light spin-1/2 Dark Matter particles
annihilating into e+e- could be responsible for the bright 511 keV gamma ray
line observed by INTEGRAL from the galactic bulge.Comment: 10 page
Some Comments on an MeV Cold Dark Matter Scenario
We discuss several aspects of astroparticle physics pertaining to a new model
with MeV cold dark matter particles, which annihilate to electron-positron
pairs in a manner yielding the correct CDM density required today, and
explaining the enhanced electron-positron annihilation line from the center of
the Galaxy. We note that the mass of the vector meson mediating the
annihilations, should exceed the mass of CDM particle, and comment on possible
enhancement due to CDM clustering, on the detectability of the new CDM, and on
particle physics models incorporating this scenario.Comment: 13 pages, 2 figures. v2 - Added some remarks regarding a more
stringent mass bound. References added, some typos corrected. v3 - Added a
comment regarding the invalidity of perturbative calculation in the case of a
very small coupling g'. Removed the comment regarding the smallness of the
angular width of the 511 keV lin
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
Probing the SUSY breaking scale at an collider
If supersymmetry is spontaneously at a low energy scale then the resulting
gravitino would be very light. The interaction strength of the longitudinal
components of such a light gravitino to electron-selectron pair then becomes
comparable to that of electroweak interactions. Such a light gravitino could
modify the cross-section for e^_L e^_R-->\tilde {e}_L\tilde {e}_R from its
MSSM value. Precision measurement of this cross-section could therefore be used
to probe the low energy SUSY breaking scale.Comment: Plain Tex, 7 pages, No figure
Constraints on Light Dark Matter and U bosons, from psi, Upsilon, K+, pi0, eta and eta' decays
Following searches for photinos and very light gravitinos in invisible decays
of psi and Upsilon, we discuss new limits on Light Dark Matter and U bosons,
from psi and Upsilon decays, as well as rare decays of K+ and invisible decays
of pi0, eta and eta' ... . The new limits involving the vector couplings of the
U to quarks turn out, not surprisingly, to be much less restrictive than
existing ones on axial couplings, from an axionlike behavior of a light U
boson, tested in psi --> gamma U, Upsilon --> gamma U and K+ --> pi+ U decays
(or as compared to the limit from parity-violation in atomic physics, in the
presence of an axial coupling to the electron). Altogether the hypothesis of
light U bosons, and light dark matter particles, remains compatible with
particle physics constraints, while allowing for the appropriate annihilation
cross sections required, both at freeze-out (for the relic abundance) and
nowadays (if e+ from LDM annihilations are at the origin of the 511 keV line
from the galactic bulge).Comment: 8 page
Supersymmetry and Gauge Invariance Constraints in a U(1)U(1)-Higgs Superconducting Cosmic String Model
A supersymmetric extension of the -Higgs bosonic
superconducting cosmic string model is considered,and the constraints imposed
upon such a model due to renormalizability, supersymmetry, and gauge invariance
are examined. For a simple model with a single chiral superfield and a
single chiral superfield, the Witten mechanism for bosonic
superconductivity (giving rise to long range gauge fields outside of the
string) does not exist. The simplest model that can accommodate the requisite
interactions requires five chiral supermultiplets. This superconducting cosmic
string solution is investigated.Comment: 17 pages, revtex, no figures; to appear in Phys. Rev.
Integral and Light Dark Matter
The nature of Dark Matter remains one of the outstanding questions of modern
astrophysics. The success of the Cold Dark Matter cosmological model argues
strongly in favor of a major component of the dark matter being in the form of
elementary particles, not yet discovered. Based on earlier theoretical
considerations, a possible link between the recent SPI/INTEGRAL measurement of
an intense and extended emission of 511 keV photons (positron annihilation)
from the central Galaxy, and this mysterious component of the Universe, has
been established advocating the existence of a light dark matter particle at
variance with the neutralino, in general considered as very heavy. We show that
it can explain the 511 keV emission mapped with SPI/INTEGRAL without
overproducing undesirable signals like high energy gamma-rays arising from
decays, and radio synchrotron photons emitted by high energy
positrons circulating in magnetic fields. Combining the annihilation line
constraint with the cosmological one (i.e. that the relic LDM energy density
reaches about 23% of the density of the Universe), one can restrict the main
properties of the light dark matter particle. Its mass should lie between 1 and
100 MeV, and the required annihilation cross section, velocity dependent,
should be significantly larger than for weak interactions, and may be induced
by the virtual production of a new light neutral spin 1 boson . On
astrophysical grounds, the best target to validate the LDM proposal seems to be
the observation by SPI/INTEGRAL and future gamma ray telescopes of the
annihilation line from the Sagittarius dwarf galaxy and the Palomar-13 globular
cluster, thought to be dominated by dark matter.Comment: 7 pages, 0 figures. To appear in the Proceedings of the 5th INTEGRAL
Workshop: "The INTEGRAL Universe", February 16-20, 2004, Munich, German
Testing the equivalence principle: why and how?
Part of the theoretical motivation for improving the present level of testing
of the equivalence principle is reviewed. The general rationale for optimizing
the choice of pairs of materials to be tested is presented. One introduces a
simplified rationale based on a trichotomy of competing classes of theoretical
models.Comment: 11 pages, Latex, uses ioplppt.sty, submitted to Class. Quantum Gra
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