118339485
Two-component dark matter
A bstractWe study an extension of the Standard Model (SM) with two interacting cold Dark Matter (DM) candidates: a neutral Majorana fermion (ν) and a neutral scalar singlet (φ). The scalar φ interacts with the SM through the “Higgs portal” coupling while ν at the tree level interacts only with φ through Yukawa interactions. The relic abundance of ν and φ is found by solving the Boltzmann equations numerically; for the case mν > mφ we also derive a reliable approximate analytical solution. Effects of the interaction between the two DM components are discussed. A scan over the parameter space is performed to determine the regions consistent with the WMAP data for DM relic abundance, and with the XENON100 direct detection limits for the DM-nucleus cross section. We find that although a large region of the parameter space is allowed by the WMAP constraints, the XENON100 data severely restricts the parameter space. Taking into account only amplitudes generated at the tree level one finds three allowed regions for the scalar mass: mφ ~ 62.5 GeV (corresponding to the vicinity of the Higgs boson resonance responsible for φφ annihilation into SM particles), mφ ≃ 130 − 140 GeV and mφ ≳ 3 TeV. 1-loop induced ν-nucleon scattering has been also calculated and discussed. A possibility of DM direct detection by the CREST-II experiment was considered.
118491017
Supersymmetric left–right model with radiative neutrino mass and multipartite dark matter
We propose a unified extension of the standard model with three types of coexisting dark matter, motivated by three well-studied scenarios: (1) supersymmetry with $$R$$R-parity conservation, (2) left–right symmetry where the $${SU}(2)_R$$SU(2)R doublet is not $$(\nu ,e)_R$$(ν,e)R but $$(n,e)_R$$(n,e)R where $$n$$n is a dark-matter candidate, and (3) a one-loop radiative neutrino mass model where the particles in the loop have an odd $$Z_2$$Z2 symmetry, the lightest of which is also a dark-matter candidate. Whereas there are many new particles in this model, the gauge couplings get unified in the same way as in the minimal supersymmetric standard model (MSSM). Since there are at least three dark-matter candidates, each one’s share of the total relic density of the Universe is adjustable, allowing for a much larger parameter space for the MSSM candidate itself. Our main focus is a careful study of a possible specific multipartite dark-matter scenario in this context.
14407716
Nonuniversal scalar masses: A signal-based analysis for the CERN Large Hadron Collider
We study the possible signatures of nonuniversal scalar masses in supersymmetry at the Large Hadron Collider (LHC). This is done, following our recent study on gaugino nonuniversality, via a multichannel analysis, based largely on the ratios of event rates for different final states, aimed at minimizing irregularity in the pattern due to extraneous effects and errors. We have studied (a) squark-slepton nonuniversality, (b) nonuniversality in sfermion masses of the third family, (c) the effects of SO(10) D-terms in supersymmetric grand unified theories. After presenting an elaborate numerical analysis of like- and opposite-sign dileptons, inclusive and hadronically quiet trileptons, as well as inclusive jet final states, we point out specific features of the spectrum in each case, which can be differentiated in the above channels from the spectrum for a minimal supergravity scenario with a universal scalar mass at high scale. The event selection criteria and the situations where the signals are sizable enough for a comparative study, are also delineated. It is found that, with some exceptions, the trilepton channels are likely to be especially useful for this purpose.
55809021
Heptagonic symmetry for quarks and leptons
The non-Abelian discrete symmetry D(7) of the heptagon is successfully applied to both quark and lepton mass matrices, including CP violation.
123789901
Dark Matter Pions
We study the scenario where dark matter corresponds to a set of pseudoGoldstone bosons, that we call dark pions, generated by the spontaneous breaking of a symmetry in the dark sector. As a concrete example, we consider an SU(N)×SU(N) broken to the diagonal subgroup that remains an exact symmetry that ensures the stability of the dark pions, and allows a novel-interactions involving neutral gauge bosons and 3 dark pions. We study both experimental and theoretical constraints, and show that the model can accommodate all data in wide regions of parameter space.
10611151
Unitarity violation in sequential neutrino mixing in a model of extra dimensions
We give the first demonstration of unitarity violation in the sequential neutrino mixing matrix in a scenario with extra compact spacelike dimensions. Gauge singlet neutrinos are assumed to propagate in one extra dimension, giving rise to an infinite tower of states in the effective four-dimensional theory. It is shown that this leads to small lepton-number violating entries in the neutrino mass matrix, which can violate unitarity on the order of 1%.
117279651
Black holes and the positive cosmological constant
We address some aspects of black hole spacetimes endowed with a positive cosmological constant, i.e. black holes located inside a cosmological event horizon. First we establish a general criterion for existence of cosmological event horizons. Using the geometrical set up built for this, we study classical black hole no hair theorems for both static and stationary axisymmetric spacetimes. We discuss cosmic Nielsen-Olesen strings as hair in Schwarzschild-de Sitter spacetime. We also give a general calculation for particle creation by a Killing horizon using complex path analysis and using this we study particle creation in Schwarzschild-de Sitter spacetime by both black hole and the cosmological event horizons.
59390019
Can a black hole with conformal scalar hair rotate
It is shown that, under the separability assumption for the metric, the slow-rotation approximation for the Bocharova-Bronnikov-Melnikov-Bekenstein black hole in general relativity with a conformally coupled scalar field does not work outside the event horizon. Suggestions indicated by our present analysis towards a fully rotating black hole solution are discussed.
118589509
A note on Hawking radiation via complex path analysis
As long as we neglect backreaction, the Hawking temperature of a given black hole would not depend upon the parameters of the particle species we are considering. In the semiclassical complex path analysis approach of Hawking radiation, this has been verified by taking scalar and Dirac spinors separately for different stationary spacetime metrics. Here we show in a coordinate-independent way that for an arbitrary spacetime with any number of dimensions, the equations of motion for a Dirac spinor, a vector, spin-2 and spin- fields reduce to Klein–Gordon equations in the WKB semiclassical limit. We then obtain, under some suitable assumptions, the complex solutions of those resulting scalar equations across the Killing horizon of a stationary spacetime to get a coordinate-independent expression for the emission probability identical for all particle species. Finally we consider some explicit examples to demonstrate the validity of that expression.
118407015
On the existence of cosmological event horizons
We show that, for general static or axisymmetric stationary spacetimes, a cosmological Killing horizon exists only if Rabnanb < 0 for a hypersurface orthogonal timelike na, at least over some portion of the region of interest of the manifold. This implies violation of the strong energy condition by the matter fields, the simplest example of which is a positive cosmological constant.
118575846
Massive spin-2 and spin-1/2 no hair theorems for stationary axisymmetric black holes
We present a proof of the no hair theorems corresponding to free massive non-perturbative PauliFierz spin-2 and perturbative massive spin- 1 fields for stationary axisymmetric de Sitter black hole spacetimes of dimension four with two commuting Killing vector fields. The applicability of these results for asymptotically flat and anti-de Sitter spacetimes are also discussed.