882 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
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
Effect of quantum fluctuations on topological excitations and central charge in supersymmetric theories
The effect of quantum fluctuations on Bogomol'nyi-Prasad-Sommerfield
(BPS)-saturated topological excitations in supersymmetric theories is studied.
Focus is placed on a sequence of topological excitations that derive from the
same classical soliton or vortex in lower dimensions and it is shown that their
quantum characteristics, such as the spectrum and profile, differ critically
with the dimension of spacetime. In all the examples examined the supercharge
algebra retains its classical form although short-wavelength fluctuations may
modify the operator structure of the central charge, yielding an anomaly. The
central charge, on taking the expectation value, is further affected by
long-wavelength fluctuations, and this makes the BPS-excitation spectra only
approximately calculable in some low-dimensional theories. In four dimensions,
in contrast, holomorphy plays a special role in stabilizing the BPS-excitation
spectra against quantum corrections. The basic tool in our study is the
superfield supercurrent, from which the supercharge algebra with a central
extension is extracted in a supersymmetric setting. A general method is
developed to determine the associated superconformal anomaly by considering
dilatation directly in superspace.Comment: 10 pages, Revtex, to appear in PR
Effective Two Higgs Doublets in Nonminimal Supersymmetric Models
The Higgs sectors of supersymmetric extensions of the Standard Model have two
doublets in the minimal version (MSSM), and two doublets plus a singlet in two
others: with (UMSSM) and without (NMSSM) an extra U(1)'. A very concise
comparison of these three models is possible if we assume that the singlet has
a somewhat larger breaking scale compared to the electroweak scale. In that
case, the UMSSM and the NMSSM become effectively two-Higgs-doublet models
(THDM), like the MSSM. As expected, the mass of the lightest CP-even neutral
Higgs boson has an upper bound in each case. We find that in the NMSSM, this
bound exceeds not very much that of the MSSM, unless tan(beta) is near one.
However, the upper bound in the UMSSM may be substantially enhanced.Comment: 8 pages, 1 table, 3 figure
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