arXiv subjects

A. B. Lahanas

Publications and source records attributed to A. B. Lahanas.

At least 37 records · Page 2Linked to original sources

arXiv2006

Dilaton and off-shell (non-critical string) effects in Boltzmann equation for species abundances

In this work we derive the modifications to the Boltzmann equation governing the cosmic evolution of relic abundances induced by dilaton dissipative-source and non-critical-string terms in dilaton-driven non-equilibrium string Cosmologies. We also discuss briefly the most important phenomenological consequences, including modifications of the constraints on the available parameter space of cosmologically appealing particle physics models, imposed by recent precision data of astrophysical measurements.

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arXiv2006

Dissipative Liouville Cosmology: A Case Study

We consider solutions of the cosmological equations pertaining to a dissipative, dilaton-driven off-equilibrium Liouville Cosmological model, which may describe the effective field theoretic limit of a non-critical string model of the Universe. The non-criticality may be the result of an early-era catastrophic cosmic event, such as a big-bang, brane-world collision etc. The evolution of the various cosmological parameters of the model are obtained, and the effects of the dilaton and off-shell Liouville terms, including briefly those on relic densities, which distinguish the model from conventional cosmologies, are emphasised.

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arXiv2004

Partial wave treatment of Supersymmetric Dark Matter in the presence of CP - violation

We present an improved partial wave analysis of the dominant LSP annihilation channel to a fermion-antifermion pair which avoids the non-relativistic expansion being therefore applicable near thresholds and poles. The method we develop allows of contributions of any partial wave in the total angular momentum J in contrast to partial wave analyses in terms of the orbital angular momentum L of the initial state, which is usually truncated to p-waves, and yields very accurate results. The method is formulated in such a way as to allow easy handling of CP-violating phases residing in supersymmetric parameters. We apply this refined partial wave technique in order to calculate the neutralino relic density in the constrained MSSM (CMSSM) in the presence of CP-violating terms occurring in the Higgs - mixing parameter μand trilinear A coupling for large tanb. The inclusion of CP-violating phases in mu and A does not upset significantly the picture and the annihilation of the LSP's to a b b_bar, through Higgs exchange, is still the dominant mechanism in obtaining cosmologically acceptable neutralino relic densities in regions far from the stau-coannihilation and the `focus point'. Significant changes can occur if we allow for phases in the gaugino masses and in particular the gluino mass.

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arXiv2004

On the brane coupling of Unified orbifolds with gauge interactions in the bulk

In the on-shell formulation of $D=5 $, N=2 supergravity, compactified on $S^1/Z_2$, we extend the results of Mirabelli and Peskin describing the interaction of the bulk fields with matter which is assumed to be confined on the brane. The novel characteristics of this approach are : Propagation of both gravity and gauge fields in the bulk, which offers an alternative for a unified description of models in extra dimensions and use of the on-shell formulation avoiding the complexity of off-shell schemes which involve numerous auxiliary fields. We also allow for nontrivial superpotential interactions of the chiral matter fields. The method we employ uses the N{\" o}ther procedure and our findings are useful for building models advocating propagation of the gauge degrees of freedom in the bulk, in addition to gravity.

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arXiv2003

WMAPing the Universe: Supersymmetry, Dark Matter, Dark Energy, Proton Decay and Collider Physics

In this review we discuss constraints on minimal supersymmetric models of particle physics implied by the recent astrophysical observations of WMAP. Although the prospects of detecting supersymmetry increase and 90 percent of the available MSSM parameter space can safely be reached by the sensitivity of future colliders, nevertheless we pay particular emphasis on discussing regions of the appropriate phase diagrams, which -if realized - would imply that detection of supersymmetry, at least in the context of minimal models, could be out of colliders reach. We also discuss the importance of a precise determination of the radiative corrections to the muon anomalous magnetic moment, both theoretically and experimentally. Finally, we briefly commend upon recent evidence, supported by observations, on a dark energy component of the Universe, of as yet unknown origin, covering 73 percent of its energy content.

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arXiv2003

WMAPing out Supersymmetric Dark Matter and Phenomenology

The recent WMAP data provide a rather restricted range of the Cold Dark Matter (CDM) density $ Ω_{CDM} h^2 $ of unprecedented accuracy. We combine these new data along with data from BNL E821 experiment measuring $ {(g_μ-2)}$, $ $the {$b\goes s γ$} branching ratio and the light Higgs boson mass bound from LEP, to update our analysis of the allowed boundaries in the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM). The prospects of measuring Supersymmetry at LHC look like a very safe bet, and the potential of discovering SUSY particles at a $ \sqrt{s} = 1.1 \mathrm{TeV} $ linear collider is enhanced considerably. The implications for Dark Matter direct searches are also discussed.

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arXiv2002

Updating the constraints to CMSSM from cosmology and accelerator experiments

The recent data from E821 Brookhaven experiment in conjunction with a new determination of the hadronic vacuum polarization contribution to the anomalous magnetic moment of muon, put new bounds on the parameters of the Constrained Minimal Supersymmetric Standard Model. We study the impact this experimental information, along with the $b \goes s γ$ branching ratio and light Higgs boson mass bound from LEP, to constrain regions of the model which are consistent with the cosmological data. The effect of these to Dark Matter direct searches is also discussed.

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arXiv2002

Supersymmetric Dark Matter and Recent Experimental Constraints

In this talk we discuss the impact of recent experimental information, like the revised bound from E821 Brookhaven experiment on $g_μ-2$ and light Higgs boson mass bound from LEP, in delineating regions of the parameters of the Constrained Minimal Supersymmetric Standard Model which are consistent with the cosmological data. The effect of these to Dark Matter direct searches is also discussed.

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arXiv2001

Combining Supersymmetric Dark Matter with Recent Accelerator Data

In the framework of the Constrained Minimal Supersymmetric Standard Model we discuss the impact of the recent experimental information, especially from the E821 Brookhaven experiment on $g_μ-2$ along with the light Higgs boson mass bound from LEP, in delineating regions of the parameters which are consistent with cosmological data. The effect of these to the Dark Matter direct searches is also discussed.

hep-ph↗

arXiv2001

Implications of the Pseudo-Scalar Higgs Boson in determining the Neutralino Dark Matter

In the framework of the Constrained Minimal Supersmmetric Standard Model (CMSSM) we discuss the impact of the pseudo-scalar Higgs boson in delineating regions of the parameters which are consistent with cosmological data and E821 data on the anomalous magnetic moment of muon. For large values of the parameter $\tan β> 50$, cosmologically allowed corridors of large $m_0$, $M_{1/2}$ are opened, due to the s-channel pseudo-scalar exchange in the pair annihilation of the lightest of the neutralinos to $b \bar{b}$ or $τ\barτ$, which dominates in this region. However, no such corridors are found for values $\tan β< 50 $. Combining cosmological and E821 data puts severe upper limits on sparticle masses. We find that at LHC, but even at a $e^{+}e^{-}$ linear collider with center of mass energy $\sqrt{s} = 800\GeV$, such as TESLA, supersymmetry can be discovered, if it is based on the CMSSM.

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arXiv2001

On the Stability of the Classical Vacua in a Minimal SU(5) 5-D Supergravity Model

We consider a five-dimensional supergravity model with SU(5) gauge symmetry and the minimal field content. Studying the arising scalar potential we find that the gauging of the $U(1)_R$ symmetry of the five-dimensional supergravity causes instabilities. Lifting the instabilities the vacua are of Anti-de-Sitter type and SU(5) is broken along with supersymmetry. Keeping the $U(1)_R$ ungauged the potential has flat directions along which supersymmetry is unbroken.

hep-th↗

arXiv2001

Dark Matter Direct Searches and the Anomalous Magnetic Moment of Muon

In the framework of the Constrained Minimal Supersymmetric Standard Model (CMSSM) we discuss the impact of the recent experimental information, especially from E821 Brookhaven experiment on $g_μ-2$ along with the light Higgs boson mass bound from LEP, to the Dark Matter direct searches. Imposing these experimental bounds, the maximum value of the spin-independent neutralino-nucleon cross section turns out to be of the order of $10^{-8}$ pb for large values of $\tanβ$ and low $M_{1/2}, m_0$. The effect of the recent experimental bounds is to decrease the maximum value of the cross section by about an order of magnitude, demanding the analogous sensitivity from the direct Dark Matter detection experiments.

hep-ph↗

arXiv2001

Neutralino Dark Matter Elastic Scattering in a Flat and Accelerating Universe

In SUGRA inspired supersymmetric models with universal boundary conditions for the soft masses, the scalar cross section $σ_{scalar}$ for the elastic neutralino--nucleon scattering is in general several orders of magnitude below the sensitivity of current experiments. For large $\tan β$ and low $M_{1/2}, m_0$ values, the theoretically predicted $σ_{scalar}$ can approach the sensitivity of these experiments ($\approx 10^{-6} pb$) being at the same time in agreement with recent cosmological data, which impose severe restrictions on the CDM relic density, and with accelerator experiments which put lower bounds on sparticle and Higgs boson masses. Further improvement of the sensitivity of DAMA and CDMS experiments will probe the large $\tan β$ region of the parameter space in the vicinity of the boundaries of the parameter space allowed by chargino and Higgs searches.

hep-ph↗

arXiv2000

On the Radiative Corrections to the Pseudo-scalar Higgs Boson Mass

We reexamine the one-loop corrections to the mass of the pseudo-scalar Higgs boson, using the effective potential. In the absence of the chargino and neutralino contributions its mass exhibits a large scale dependence in the large $M_{1/2}$ regime, especially for values of $\tan β>20$. Thus, although of electroweak origin, the heaviness of the $M_{1/2}$, in conjunction with the largeness of $\tan β$, makes these corrections very important for establishing a scale independent result and an unambiguous determination of the pseudo-scalar mass in this region of the parameter space.

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arXiv2000

Neutralino relic density in a Universe with a non-vanishing cosmological constant

We discuss the relic density of the lightest of the supersymmetric particles in view of new cosmological data, which favour the concept of an accelerating Universe with a non-vanishing cosmological constant. Recent astrophysical observations provide us with very precise values of the relevant cosmological parameters. Certain of these parameters have direct implications on particle physics, e.g., the value of matter density, which in conjunction with electroweak precision data put severe constraints on the supersymmetry breaking scale. In the context of the Constrained Minimal Supersymmetric Standard Model (CMSSM) such limits read as: $M_{1/2} \simeq 300 \GeV - 340 \GeV$, $m_0 \simeq 80 \GeV - 130 \GeV$. Within the context of the CMSSM a way to avoid these constraints is either to go to the large $\tan β$ and $μ> 0$ region, or make ${\tilde τ}_R$, the next to lightest supersymmetric particle (LSP), be almost degenerate in mass with LSP.

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arXiv1999

Charge asymmetry in two-Higgs doublet models

We discuss the features of a two-Higgs doublet model exhibiting a two stage phase transition. At finite temperatures electric charge violating stationary points are developed. In conjunction with {\em CP} violation in the Higgs or the Yukawa sector, the phase transition to the charge conserving vacuum, generates a net charge asymmetry $ΔQ$, in the presence of heavy leptons, which may be well above the astrophysical bounds put on $ΔQ$ unless the heavy leptons are sufficiently massive. This type of transition may be of relevance for supersymmetric extensions of the Standard Model, since it shares the same features, namely two Higgs doublets and similar {\em CP} violating sources.

hep-ph↗

arXiv1999

Neutralino Relic Density with a Cosmological Constant confronts Electroweak Precision Measurements

We discuss the relic density of the lightest of the supersymmetric particles ({\small LSP}) in view of new cosmological data, which favour the concept of an accelerating Universe with a non-vanishing cosmological constant. The new bound on the Cold Dark Matter density, $Ω_{\mathrm{CDM}} h_0^2 \lesssim 0.22$, puts stringent constraints on supersymmetry preferring low supersymmetry breaking scales, in sharp contrast to electroweak precision measurements favouring large supersymmetry breaking scales. Supersymmetric predictions are in agreement with cosmological data and electroweak precision data in the window of the parameter space: $m_0<200\GeV$, $300\GeV<M_{1/2}<400\GeV$, putting bounds on sparticle masses, which may be evaded if $m_{LSP} <m_{{\tildeτ}_R} \lesssim 1.2 m_{LSP}$.

hep-ph↗

arXiv1998

The Effective Weak Mixing Angle in the MSSM

The predictions of the MSSM are discussed in the light of recent LEP and SLD precision data. The full supersymmetric one loop corrections to the effective weak mixing angle, experimentally determined in LEP and SLD experiments, are considered. It is demonstrated, both analytically and numerically, that, potentially dangerous, large logarithmic sparticle corrections are cancelled. The relative difference factor Δk between the mixing angle defined as a ratio of couplings and the experimentally obtained angle is discussed. It is found that Δk is dominated by the oblique corrections, while the non-oblique overall supersymmetric EW and SQCD corrections are negligible. The comparison of the MSSM with radiative electroweak symmetry breaking to the LEP+SLD precision data indicates that rather large values of the soft breaking parameter M_{1/2} in the region greater than 500 GeV are preferred.

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