arXiv subjects

C. Pallis

Publications and source records attributed to C. Pallis.

82 records · Page 5Linked to original sources

arXiv2005

Massive Particle Decay and Cold Dark Matter Abundance

The decoupling of a cold relic, during a decaying-particle-dominated cosmological evolution is analyzed, the relic density is calculated both numerically and semi-analytically and the results are compared with each other. Using plausible values (from the point of view of supersymmetric models) for the mass and the thermal averaged cross section times the velocity of the cold relic, we investigate scenaria of equilibrium or non-equilibrium production. In both cases, acceptable results for the dark matter abundance can be obtained, by constraining the reheat temperature of the decaying particle, its mass and the averaged number of the produced cold relic. The required reheat temperature is in any case lower than about $20 {\rm GeV}$.

hep-ph↗

arXiv2004

Yukawa Quasi-Unification and Inflation

We review the construction of a concrete supersymmetric grand unified model, which naturally leads to a moderate violation of "asymptotic" Yukawa unification and, thus, can allow an acceptable b-quark mass within the constrained minimal supersymmetric standard model with mu>0. The model possesses a wide and natural range of parameters which is consistent with the data on the cold dark matter abundance in the universe, b-->s gamma, the muon anomalous magnetic moment and the Higgs boson masses. Also, it automatically leads to a new version of shifted hybrid inflation, which avoids overproduction of monopoles at the end of inflation by using only renormalizable terms.

hep-ph↗

arXiv2004

b-tau Unification with Gaugino and Sfermion Mass non Universality

In the context of a SUSY GUT inspired MSSM version, the low energy consequences of the asymptotic $b-τ$ Yukawa coupling Unification are examined, under the assumption of universal or non-universal boundary conditions for the gaugino and sfermion masses. Gaugino non-universality is applied, so that the SUSY corrections to $b$-quark mass can be reconciled with the present experimental data on muon anomalous magnetic moment. Restrictions on the parameter space, originating from the Cold Dark Matter abundance in the universe, the inclusive branching ratio of $b\to sγ$ and the accelerator data are, also, investigated and the scalar neutralino-proton cross section is calculated. In the case of a bino-like LSP and universal boundary conditions for the sfermion masses, the constraints, arising from the Cold Dark Matter and ${\rm BR}(b \to sγ)$ can be simultaneously satisfied, mainly thanks to the $A$-pole effect or the neutralino-stau coannihilations. In addition, sfermion mass non-universality provides the possibility of new coannihilation phenomena (neutralino-sbottom or neutralino-tau sneutrino-stau), which facilitate the simultaneous satisfaction of all the above requirements. In both cases above, the neutralino abundance can essentially decrease for a W-ino or higgsino like LSP creating regions of parameter space with additional neutralino-chargino and/or heavier neutralino coannihilations. The neutralino-sbottom mass proximity significantly ameliorates the detectability of LSP.

hep-ph↗

arXiv2003

MSSM with Yukawa Quasi-Unification

We consider the constrained minimal supersymmetric standard model which emerges from one theory with a small deviation from Yukawa unification which is adequate for $μ>0$. We show that this model possesses a wide and natural range of parameters which is consistent with the data on $b\to sγ$, the muon anomalous magnetic moment, the cold dark matter abundance in the universe, and the Higgs boson masses.

hep-ph↗

arXiv2003

Yukawa Quasi-Unification and Neutralino Relic Density

The construction of a Supersymmetric Grand Unified Model based on the Pati-Salam gauge group is briefly reviewed and the low energy consequences of the derived asymptotic Yukawa quasi-unification conditions are examined. In the framework of the resulting Constrained Minimal Supersymmetric Standard Model, the cosmological relic density of the bino-like LSP is calculated and the results are explicitly compared with {\tt micrOMEGAs}. In addition to the Cold Dark Matter constraint, restrictions on the parameter space, arising from the Higgs boson masses, the SUSY corrections to $b$-quark mass, the muon anomalous magnetic moment and the inclusive decay $b\to sγ$ are, also, investigated. For $μ>0$, a wide and natural range of parameters is allowed. On the contrary, the $μ<0$ case not only is disfavored from the present experimental data on the muon anomalous magnetic moment, but also, it can be excluded from the combination of the Cold Dark Matter and BR($b\to s γ$) requirements.

hep-ph↗

arXiv2003

On Yukawa quasi-unification with mu<0

Although recent data on the muon anomalous magnetic moment strongly disfavor the constrained minimal supersymmetric standard model with mu<0, they cannot exclude it because of theoretical ambiguities. We consider this model supplemented by a Yukawa quasi-unification condition which allows an acceptable b-quark mass. We find that the cosmological upper bound on the lightest sparticle relic abundance is incompatible with the data on the branching ratio of b-->s gamma, which is evaluated by including all the next-to-leading order corrections. Thus, this scheme is not viable.

hep-ph↗

arXiv2002

Yukawa Quasi-Unification

We construct concrete supersymmetric grand unified theories based on the Pati-Salam gauge group SU(4)_c x SU(2)_L x SU(2)_R which naturally lead to a moderate violation of "asymptotic" Yukawa unification and thus can allow an acceptable b-quark mass even with universal boundary conditions. We consider the constrained minimal supersymmetric standard model which emerges from one of these theories with a deviation from Yukawa unification which is adequate for mu>0. We show that this model possesses a wide and natural range of parameters which is consistent with the data on b --> s gamma, the muon anomalous magnetic moment, the cold dark matter abundance in the universe, and the Higgs boson masses. The lightest supersymmetric particle can be as light as about 107 GeV.

hep-ph↗

arXiv2001

Cold Dark Matter and b --> s gamma in the Horava-Witten Theory

The minimal supersymmetric standard model with complete, partial or no Yukawa unification and radiative electroweak breaking with boundary conditions from the Horava-Witten theory is considered. The parameters are restricted by constraining the lightest sparticle relic abundance by cold dark matter considerations and requiring the b-quark mass after supersymmetric corrections and the branching ratio of b --> s gamma to be compatible with data. Complete Yukawa unification can be excluded. Also, t-b Yukawa unification is strongly disfavored since it requires almost degenerate lightest and next-to-lightest sparticle masses. However, the b-tau or no Yukawa unification cases avoid this degeneracy. The latter with mu<0 is the most natural case. The lightest sparticle mass, in this case, can be as low as about 77 GeV.

hep-ph↗

arXiv2000

Yukawa Unification, b --> s gamma and Bino-Stau Coannihilation

The minimal supersymmetric standard model with universal boundary conditions and "asymptotic" Yukawa unification is considered. The full one-loop effective potential for radiative electroweak symmetry breaking as well as the one-loop corrections to the charged Higgs boson, b-quark and tau lepton masses are included. The CP-even Higgs boson masses are corrected to two-loops. The relic abundance of the lightest supersymmetric particle (bino) is calculated by including its coannihilations with the next-to-lightest supersymmetric particle (lightest stau) consistently with Yukawa unification. The branching ratio of b --> s gamma is evaluated by incorporating all the applicable next-to-leading order QCD corrections. The bino-stau coannihilations reduce the bino relic abundance below the upper bound from cold dark matter considerations in a sizable fraction of the parameter space allowed by b --> s gamma for mu>0. Thus, the mu>0 case, which also predicts an acceptable b-quark mass, is perfectly compatible with data.

hep-ph↗

arXiv2000

Supersymmetric Cold Dark Matter with Yukawa Unification

The cosmological relic density of the lightest supersymmetric particle of the minimal supersymmetric standard model is calculated under the assumption of gauge and Yukawa coupling unification. We employ radiative electroweak breaking with universal boundary conditions from gravity-mediated supersymmetry breaking. Coannihilation of the lightest supersymmetric particle, which turns out to be an almost pure bino, with the next-to-lightest supersymmetric particle (the lightest stau) is crucial for reducing its relic density to an acceptable level. Agreement with the mixed or the pure cold (in the presence of a nonzero cosmological constant) dark matter scenarios for large scale structure formation in the universe requires that the lightest stau mass is about 2-8% larger than the bino mass, which can be as low as 222 GeV. The smallest allowed value of the lightest stau mass turns out to be about 232 GeV.

hep-ph↗