arXiv subjects
Publications and source records attributed to Salah Nasri.
We consider a new effective symmetry that acts on a gauge invariant Lagrangian. We show that the standard model after spontaneous symmetry breakdown is invariant under this symmetry which identifies up to a scale factor the gauge parameter with the elementary or composite scalars in the theory. We discuss some of the consequences of this symmetry in the abelian and non-abelian sectors of the standard model.
We consider an extension of the standard model (SM) with charged singlet scalars and right handed (RH) neutrinos all at the electroweak scale. In this model, the neutrino masses are generated at three loops, which provide an explanation for their smallness, and the lightest RH neutrino, $N_{1}$, is a dark matter candidate. We find that for three generations of RH neutrinos, the model can be consistent with the neutrino oscillation data, lepton flavor violating processes, $N_{1}$ can have a relic density in agreement with the recent Planck data, and the electroweak phase transition can be strongly first order. We also show that the charged scalars may enhance the branching ratio $h-->YY$, where as $h-->YZ$ get can get few percent suppression. We also discuss the phenomenological implications of the RH neutrinos at the collider.
We reconsider top condensate models from the perspective that not only two quark composite fields can form but also four quark ones. We obtain a model which contains a Higgs doublet and a Higgs triplet, where one of the neutral components of the Higgs triplet identifies with the Higgs boson found at the LHC. We discuss some of the phenomenological consequences.
We study the implications of a criterion of naturalness for a simple two Higgs doublet model in the context of the discovery of a Higgs like particle with a mass at 125 GeV. This condition which measures the amount of fine tuning further limits the parameter space of this particular model and together with other phenomenological constraints leads to an allowed range of masses for the other neutral or charged Higgs bosons: H, a^{\pm}, a^0.
We study via the renormalization group equations at one-loop order the perturbativity and vacuum stability of a two-singlet model of cold dark matter (DM) that consists in extending the Standard Model with two real gauge-singlet scalar fields. We then investigate the regions in the parameter space in which the model is viable. For this, we require the model to reproduce the observed DM relic density abundance, to comply with the measured XENON 100 direct-detection upper bounds, and to be consistent with the RGE perturbativity and vacuum-stability criteria up to $40\mathrm{TeV}$. For small mixing angle $θ$ between the physical Higgs $h$ and auxiliary field, and DM-$h$ mutual coupling constant $λ_{0}^{(4)}$, we find that the auxiliary-field mass is confined to the interval $116\mathrm{GeV}-138\mathrm{GeV}$ while the DM mass is mainly confined to the region above $57\mathrm{GeV}$. Increasing $θ$ enriches the existing viability regions without relocating them, while increasing $λ_{0}^{(4)}$ shrinks them with a tiny relocation. We show that the model is consistent with the recent Higgs boson-like discovery by the ATLAS and CMS experiments, while very light dark matter (masses below $5\mathrm{GeV}$) is ruled out by the same experiments.
We propose a minimal extension of the Standard Model by two real singlet fields that could provide a good candidate for light Dark Matter, and give a strong first order electroweak phase transition. As a result, there are two CP even scalars; one is lighter than \sim 70 GeV, and the other one with mass in the range of 280-400 GeV; and consistent with electroweak precision tests. We show that the light scalar mass can be as small as 25 GeV while still being consistent with the LEP data. The predicted dark matter scattering cross section is large enough to accommodate CoGeNT and can be probed by future XENON experiment. We also show that for dark matter mass around 2 GeV, the branching fraction of the process (B^+\rightarrowK^++2(DM)) can be accessible in SuperB factories.
We study the implications of phenomenological processes on a two-singlet extension of the Standard Model we introduced in a previous work to describe light cold dark matter. We look into the rare decays of $Υ$ and $B$ mesons, most particularly the invisible channels, and study the decay channels of the Higgs particle. Preferred regions of the parameter space are indicated, together with others that are excluded. Comments in relation to recent Higgs searches and finds at the LHC are made.
In this work, we have investigated the nature of the electroweak phase transition in the U(1) extended minimal supersymmetric standard model without introducing any exotic fields. The effective potential has been estimated exactly at finite temperature taking into account the whole particle spectrum. For reasonable values of the lightest Higgs and neutralino, we found that the electroweak phase transition could be strongly first order due to: (1) the interactions of the singlet with the doublets in the effective potential, and (2) the evolution of the wrong vacuum that delays the transition.
We extend the Standard Model by adding two gauge-singlet $\mathbb{Z}_{2}$% -symmetric scalar fields that interact with visible matter only through the Higgs particle. One is a stable dark matter WIMP, and the other one undergoes a spontaneous breaking of the symmetry that opens new channels for the dark matter annihilation, hence lowering the mass of the WIMP. We study the effects of the observed dark matter relic abundance on the annihilation cross section and find that in most regions of the parameters space, light dark matter is viable. We also compare the elastic scattering cross-section of our dark matter candidate off nucleus with existing (CDMSII and XENON100) and projected (SuperCDMS and XENON1T) experimental exclusion bounds. We find that most of the allowed mass range for light dark matter will be probed by the projected sensitivity of XENON1T experiment.
We study a simple two Higgs doublet model which reflects, in a phenomenological way, the idea of compositeness for the Higgs sector. It is relatively predictive. In one scenario, it allows for a "hidden" usual Higgs particle in the 100 GeV region and a possible dark matter candidate.
Long-lived colored particles with masses m > 200 GeV are allowed by current accelerator searches, and are predicted by a number of scenarios for physics beyond the standard model. We argue that such "heavy partons'' effectively have a geometrical cross section (of order 10 mb) for annihilation at temperatures below the QCD deconfinement transition. The annihilation process involves the formation of an intermediate bound state of two heavy partons with large orbital angular momentum. The bound state subsequently decays by losing energy and angular momentum to photon or pion emission, followed by annihilation of the heavy partons. This decay occurs before nucleosynthesis for m < 10^{11} GeV for electrically charged partons and m < TeV for electrically neutral partons. This implies that heavy parton lifetimes as long as 10^{14} sec are allowed even for heavy partons with m ~ TeV decaying to photons or hadrons with significant branching fraction.
The recently measured unexpected neutrino mixing patterns have caused a resurgence of interest in the study of finite flavor groups with two- and three-dimensional irreducible representations. This paper details the mathematics of the two finite simple groups with such representations, the Icosahedral group A_5, a subgroup of SO(3), and PSL_2(7), a subgroup of SU(3).
We consider a scenario where a supersymmetric model has multiple dark matter particles. Adding a U(1)' gauge symmetry is a well-motivated extension of the Minimal Supersymmetric Standard Model (MSSM). It can cure the problems of the MSSM such as the mu-problem or the proton decay problem with high-dimensional lepton number and baryon number violating operators which R-parity allows. An extra parity (U-parity) may arise as a residual discrete symmetry after U(1)' gauge symmetry is spontaneously broken. The Lightest U-parity Particle (LUP) is stable under the new parity becoming a new dark matter candidate. Up to three massive particles can be stable in the presence of the R-parity and the U-parity. We numerically illustrate that multiple stable particles in our model can satisfy both constraints from the relic density and the direct detection, thus providing a specific scenario where a supersymmetric model has well-motivated multiple dark matters consistent with experimental constraints. The scenario provides new possibilities in the present and upcoming dark matter searches in the direct detection and collider experiments.
The Non-Abelian finite group PSL_2(7) is the only simple subgroup of SU(3) with a complex three-dimensional irreducible representation. It has two maximal subgroups, S_4 which, along with its own A_4 subgroup, has been successfully applied in numerous models of flavor, as well as the 21 element Frobenius group Z_7 x Z_3, which has gained much less attention. We show that it can also be used to generate tri-bimaximal mixing in the neutrino sector, while allowing for quark and charged lepton hierarchies.
The left-handed sneutrino in the Minimal Supersymmetric Standard Model (MSSM) has been ruled out as a viable thermal dark matter candidate, due to conflicting constraints from direct detection experiments and from the measurement of the dark matter relic density. The intrinsic fine-tuning problem of the MSSM, however, motivates an extension with a new U(1)' gauge symmetry. We show that in the U(1)'-extended MSSM the right-handed sneutrino becomes a good thermal dark matter candidate. We identify two generic parameter space regions where the combined constraints from relic density determinations, direct detection and collider searches are all satisfied.
The large neutrino mixing angles have generated interest in finite subgroups of SU(3), as clues towards understanding the flavor structure of the Standard Model. In this work, we study the mathematical structure of the simplest non-Abelian subgroup, Delta(3n^2). Using simple mathematical techniques, we derive its conjugacy classes, character table, build its irreducible representations, their Kronecker products, and its invariants.
We show that in a class of universal extra dimension (UED) models that solves both the neutrino mass and proton decay problems using low scale left-right symmetry, the dark matter of the Universe consists of an admixture of KK photon and KK right-handed neutrinos. We present a full calculation of the dark matter density in these models taking into account the co-annihilation effects due to near by states such as the scalar partner of the KK photon as well as fermion states near the right-handed KK neutrino. Using the value of the relic CDM density, we obtain upper limits on $R^{-1}$ of about 400-650 GeV and $M_{Z'}\leq 1.5$ TeV, both being accessible to LHC. For a region in this parameter space where the KK right-handed neutrino contributes significantly to the total relic density of dark matter, we obtain a lower bound on the dark matter-nucleon scattering cross section of $10^{-44}$ cm$^2$, which can be probed by the next round of dark matter search experiments.
The PVLAS experiment has recently claimed evidence for an axion-like particle in the milli-electron-Volt mass range with a coupling to two photons that appears to be in contradiction with the negative results of the CAST experiment searching for solar axions. The simple axion interpretation of these two experimental results is therefore untenable and it has posed a challenge for theory. We propose a possible way to reconcile these two results by postulating the existence of an ultralight pseudo-scalar particle interacting with two photons and a scalar boson and the existence of a low scale phase transition in the theory.