520 research outputs found
Hints of Standard Model Higgs Boson at the LHC and Light Dark Matter Searches
The most recent results of searches at the LHC for the Higgs boson h have
turned up possible hints of such a particle with mass m_h about 125 GeV
consistent with standard model (SM) expectations. This has many potential
implications for the SM and beyond. We consider some of them in the contexts of
a simple Higgs-portal dark matter (DM) model, the SM plus a real gauge-singlet
scalar field D as the DM candidate, and a couple of its variations. In the
simplest model with one Higgs doublet and three or four generations of
fermions, for D mass m_D DD tends to have a
substantial branching ratio. If future LHC data confirm the preliminary Higgs
indications, m_D will have to exceed m_h/2. To keep the DM lighter than m_h/2,
one will need to extend the model and also satisfy constraints from DM direct
searches. The latter can be accommodated if the model provides sizable isospin
violation in the DM-nucleon interactions. We explore this in a
two-Higgs-doublet model combined with the scalar field D. This model can offer
a 125-GeV SM-like Higgs and a light DM candidate having isospin-violating
interactions with nucleons at roughly the required level, albeit with some
degree of fine-tuning.Comment: 17 pages, 4 figures, slightly revised, main conclusions unchanged,
references added, matches published versio
DAMA detection claim is still compatible with all other DM searches
We show that the annual modulation signal observed by DAMA can be reconciled
with all other negative results from dark matter searches with a conventional
halo model for particle masses around 5 to 9 GeV. We also show which particular
dark matter stream could produce the DAMA signal.Comment: Talk given at TAUP2005, Sept. 10-14 2005, Zaragoza (Spain). 3 pages,
4 figure
GZK photons as UHECR above 10 eV
"GZK photons" are produced by extragalactic nucleons through the resonant
photoproduction of pions. We present the expected range of the GZK photon
fraction of UHECR, assuming a particular UHECR spectrum and primary nucleons,
and compare it with the minimal photon fraction predicted by Top-Down models.Comment: Talk given at TAUP2005, Sept. 10-14 2005, Zaragoza (Spain); 3 pages,
2 figure
Gravitational wave signatures from discrete flavor symmetries
Non-Abelian discrete symmetries have been widely used to explain the patterns of lepton masses and flavor mixing. In these models, a given symmetry is assumed at a high scale and then is spontaneously broken by scalars (the flavons), which acquire vacuum expectation values. Typically, the resulting leading order predictions for the oscillation parameters require corrections in order to comply with neutrino oscillation data. We introduce such corrections through an explicit small breaking of the symmetry. This has the advantage of solving the cosmological problems of these models without resorting to inflation. The explicit breaking induces an energy difference or "bias"between different vacua and drives the evolution of the domain walls, unavoidably produced after the symmetry breaking, towards their annihilation. Importantly, the wall annihilation leads to gravitational waves which may be observed in current and/or future experiments. We show that a distinctive pattern of gravitational waves with multiple overlapped peaks is generated when walls annihilate, which is within the reach of future detectors. We also show that cosmic walls from discrete flavor symmetries can be cosmologically safe for any spontaneous breaking scale between 1 and 1018 GeV, if the bias is chosen adequately, without the need to inflate the walls away. We use as an example a particular A4 model in which an explicit breaking is included in right-handed neutrino mass terms
Associated single photons and doubly charged scalar at linear e-e- colliders
Doubly charged scalars, predicted in many models having exotic Higgs
representations, can in general have lepton-number violating (LFV) couplings.
We show that by using an associated monoenergetic final state photon seen at a
future linear e-e- collider, we can have a clear and distinct signature for a
doubly-charged resonance. The strength of the Delta L=2 coupling can also be
probed quite effectively as a function of the recoil mass of the doubly-charged
scalar.Comment: Reference adde
Anisotropy of the Cosmic Neutrino Background
The cosmic neutrino background (CNB) consists of low-energy relic neutrinos
which decoupled from the cosmological fluid at a redshift z ~ 10^{10}. Despite
being the second-most abundant particles in the universe, direct observation
remains a distant challenge. Based on the measured neutrino mass differences,
one species of neutrinos may still be relativistic with a thermal distribution
characterized by the temperature T ~ 1.9K. We show that the temperature
distribution on the sky is anisotropic, much like the photon background,
experiencing Sachs-Wolfe and integrated Sachs-Wolfe effects.Comment: 5 pages, 2 figures / updated references, discussion of earlier wor
Charged Vacuum Bubble Stability
A type of scenario is considered where electrically charged vacuum bubbles,
formed from degenerate or nearly degenerate vacuua separated by a thin domain
wall, are cosmologically produced due to the breaking of a discrete symmetry,
with the bubble charge arising from fermions residing within the domain wall.
Stability issues associated with wall tension, fermion gas, and Coulombic
effects for such configurations are examined. The stability of a bubble depends
upon parameters such as the symmetry breaking scale and the fermion coupling. A
dominance of either the Fermi gas or the Coulomb contribution may be realized
under certain conditions, depending upon parameter values.Comment: 16 pages,revtex; accepted for publication in Phys.Rev.
Light-Heavy Symmetry: Geometric Mass Hierarchy for Three Families
The Universal Seesaw pattern coupled with a LightHeavy
symmetry principle leads to the Diophantine equation , where and distinct. Its unique non-trivial
solution gives rise to the geometric mass hierarchy ,
, for fermion families. This is realized in
a model where the hybrid (yet UpDown symmetric) quark mass
relations play a
crucial role in expressing the CKM mixings in terms of simple mass ratios,
notably .Comment: 12 pages, no figures, Revtex fil
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