881 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
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
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.
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
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
Implications of Low Energy Supersymmetry Breaking at the Tevatron
The signatures for low energy supersymmetry breaking at the Tevatron are
investigated. It is natural that the lightest standard model superpartner is an
electroweak neutralino, which decays to an essentially massless Goldstino and
photon, possibly within the detector. In the simplest models of gauge-mediated
supersymmetry breaking, the production of right-handed sleptons, neutralinos,
and charginos leads to a pair of hard photons accompanied by leptons and/or
jets with missing transverse energy. The relatively hard leptons and softer
photons of the single e^+e^- \gamma \gamma + \EmissT event observed by CDF
implies this event is best interpreted as arising from left-handed slepton pair
production. In this case the rates for l^{\pm} \gamma \gamma + \EmissT and
\gamma \gamma + \EmissT are comparable to that for l^+l^- \gamma \gamma +
\EmissT.Comment: 18 pages, Latex, tables correcte
Fitting Neutrino Physics with a U(1)_R Lepton Number
We study neutrino physics in the context of a supersymmetric model where a
continuous R-symmetry is identified with the total Lepton Number and one
sneutrino can thus play the role of the down type Higgs. We show that
R-breaking effects communicated to the visible sector by Anomaly Mediation can
reproduce neutrino masses and mixing solely via radiative contributions,
without requiring any additional degree of freedom. In particular, a relatively
large reactor angle (as recently observed by the Daya Bay collaboration) can be
accommodated in ample regions of the parameter space. On the contrary, if the
R-breaking is communicated to the visible sector by gravitational effects at
the Planck scale, additional particles are necessary to accommodate neutrino
data.Comment: 19 pages, 3 figures; v2: references added, constraints updated,
overall conclusions unchange
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