arXiv subjects

Tarek Ibrahim

Publications and source records attributed to Tarek Ibrahim.

At least 37 records · Page 2Linked to original sources

arXiv2010

Large Tau and Tau Neutrino Electric Dipole Moments in Models with Vector Like Multiplets

It is shown that the electric dipole moment of the tau lepton several orders of magnitude larger than predicted by the standard model can be generated from mixings in models with vector like mutiplets. The EDM of the tau lepton arises from loops involving the exchange of the W, the charginos, the neutralinos, the sleptons, the mirror leptons, and the mirror sleptons. The EDM of the Dirac tau neutrino is also computed from loops involving the exhange of the W, the charginos, the mirror leptons and mirror sleptons. A numerical analysis is presented and it is shown that the EDMs of the tau lepton and of the tau neutrino which lie just a couple of orders of magnitude below the sensitivity of the current experiment can be achieved. Thus the predictions of the model are testable in improved experiment on the EDM of the tau and of the tau neutrino.

hep-ph↗

arXiv2009

On the Possible Observation of Mirror Matter

The possibility that mirror matter with masses in the several hundred GeV- TeV range exists is explored. Mirror matter appears quite naturally in many unified models of particle interactions both in GUTs and in strings often in vector-like combinations. Some of these vector-like multiplets could escape acquiring super heavy masses and remain light down to the low energies where they acquire vector-like masses of electroweak size. It is found that a very small mixing of the vector-like multiplets with MSSM matter (specifically with the third generation matter) can produce very large contributions to the magnetic moment of the $τ$ neutrino by as much as several orders of magnitude putting this moment in the range of accessibility of improved experiment. Further, it is shown that if mirror matter exists it would lead to distinctive signatures at colliders and thus such matter can be explored at the LHC energies with available luminosities.

hep-ph↗

arXiv2008

An MSSM Extension with a Mirror Fourth Generation, Neutrino Magnetic Moments and LHC Signatures

Recent analyses have shown that a sequential fourth generation can be consistent with precision electroweak data. We consider the possibility that the new generation could be a mirror generation with $V+A$ rather than $V-A$ interactions. Specifically we consider an extension of the minimal supersymmetric standard model with a light mirror generation (mirMSSM) . Implications of this extension are explored. One consequence is an enhancement of the tau neutrino magnetic moment by several orders of magnitude consistent with the current limits on the magnetic moment of the tau. The masses of the mirror generation arise due to electroweak symmetry breaking, and if a mirror generation exists its mass spectrum must lye below a TeV, and thus should be discovered at the LHC. Mirror particles and mirror sparticles produce many characteristic signatures which should be detectable at the LHC. Heavy higgs boson decays into mirror particles and an analysis of the forward-backward asymmetries can distinguish a mirror generation from a sequential fourth generation. The validity of the model can thus be tested at the LHC. A model of the type discussed here could arise from a more unified structure such as grand unification or strings where a mirror generation escapes the survival hypothesis, i.e., a generation and a mirror generation do not tie up to acquire a mass of size $M_{GUT}$ or $M_{string}$ due to a symmetry, and thus remain massless down to the electroweak scale.

hep-ph↗

arXiv2008

Neutralino decay of MSSM neutral Higgs bosons

We compute the one loop corrected effective Lagrangian for the neutralino-neutralino-neutral Higgs interactions $χ^{0}_{\ell} χ^{0}_kH^{0}_m$. The analysis completes the previous analyses where similar corrections were computed for the $\bar{f} f H^{0}_m$ couplings, where $f$ stands for Standard Model quarks and leptons and for the chargino-chargino-neutral Higgs couplings $χ^{+}_l χ^{-}_kH^{0}_m$ within the minimal supersymmetric standard model MSSM. The effective one loop Lagrangian is then applied to the computation of the neutral Higgs decays. The sizes of the supersymmetric loop corrections of the neutral Higgs decay widths into $χ^{0}_{\ell} χ^{0}_k$ (${\ell}=1,2,3,4$; $k=1,2,3,4$) are investigated and the supersymmetric loop correction is found to be in the range of $\sim 10%$ in significant regions of the parameter space. By including the loop corrections of the other decay channels $\bar{b} b$, $\bar{t} t$, $\barτ τ$, $\bar{c} c$, and $χ^{-}_i χ^{+}_j$ ($i=1,2$; $j=1,2$), the corrections to branching ratios for $H^{0}_m\to χ^{0}_{\ell} χ^{0}_k$ can reach as high as 50%. The effects of CP phases on the branching ratio are also investigated. A discussion of the implications of the analysis for colliders is given.

hep-ph↗

arXiv2008

CP Violation From Standard Model to Strings

A review of CP violation from the Standard Model to strings is given which includes a broad landscape of particle physics models, encompassing the non-supersymmetric 4D extensions of the standard model, and models based on supersymmetry, on extra dimensions, on strings and on branes. The supersymmetric models discussed include complex mSUGRA and its extensions, while the models based on extra dimensions include 5D models including models based on warped geometry. CP violation beyond the standard model is central to achieving the desired amount of baryon asymmetry in the universe via baryogenesis and leptogenesis. They also affect a variety of particle physics phenomena: electric dipole moments, $g-2$, relic density and detection rates for neutralino dark matter in supersymmetric theories, Yukawa unification in grand unified and string based models, and sparticle production cross sections, and their decays patterns and signatures at hadron colliders. Additionally CP violations can generate CP even-CP odd Higgs mixings, affect the neutral Higgs spectrum and lead to phenomena detectable at colliders. Prominent among these are the CP violation effects in decays of neutral and charged Higgs bosons. Neutrino masses introduce new sources of CP violation which will be explored in neutrino factories in the future. Such phases can also enter in proton stability in unified models of particle interactions. The current experimental status of CP violation is discussed and possibilities for the future outlined.

hep-ph↗

arXiv2007

Effective Lagrangian for the $χ^{+}_j χ^{-}_kH^{0}_l$ interaction in the minimal supersymmetric standard model and neutral Higgs decays

We extend previous analyses of the supersymmetric loop correction to the neutral Higgs couplings to include the coupling $χ^{+}_j χ^{-}_kH^{0}_l$. The analysis completes the previous analyses where similar corrections were computed for the $\barτ τH^{0}_l$, $\bar{b} b H^{0}_l$, $\bar{c} c H^{0}_l$ and for $\bar{t} t H^{0}_l$ couplings within the minimal supersymmetric standard model. The effective one loop Lagrangian is then applied to the computation of the neutral Higgs decays. The sizes of the supersymmetric loop corrections of the neutral Higgs decay widths into $χ^{+}_i χ^{-}_j$ ($i=1,2$; $j=1,2$) are investigated and the supersymmetric loop correction is found to be in the range of $7\sim15%$ in significant regions of the parameter space. By including the loop corrections of the other decay channels $\bar{b} b$, $\bar{t} t$, $\barτ τ$, $\bar{c} c$, and $χ^0_i χ^0_j$ ($i=1-4$; $j=1-4$), the corrections to branching ratios for $H^{0}_l\to χ^{+}_i χ^{-}_j$ can reach as high as 40%. The effects of CP phases on the branching ratio are also investigated.

hep-ph↗

arXiv2006

An Improved Analysis of $b\to sγ$ in Supersymmetry

An improved analysis of the $b\to s+γ$ decay in the minimal flavor violating case is given taking into account additional contributions in the supersymmetric sector which enter in the next-to-leading-order (NLO) and are enhanced by $\tanβ$ factors. Specifically, we compute a set of twenty one-loop diagrams to give the most complete analysis to date of the NLO supersymmetric corrections. These modifications are computed from the effective charged Higgs and neutral Higgs couplings involving twelve loop diagrams for the charged Higgs sector and eight loop diagrams for the neutral Higgs sector. While the computations of these corrections are available in the literature, their full forms including the complex phase dependence has not be considered. Our analysis takes account of the full allowed set of twenty one-loop diagrams and is more general since it also includes the full dependence on CP phases in non universal sugra and MSSM models. A numerical analysis is carried out to estimate the size of the corrections to $b\to s+γ$. We also briefly discuss the implications of these results for the search for supersymmetry.

hep-ph↗

arXiv2005

WMAP Dark Matter Constraints and Yukawa Unification in SUGRA models with CP Phases

The compatibility of producing the observed amount of dark matter, as indicated by the WMAP data, through the relic abundance of neutralinos with Yukawa unification and with the measured rate of $b\to s γ$ is analyzed in mSUGRA and extended SUGRA unified models with the inclusion of CP phases. The CP phases affect the analysis in several ways, e.g., through the threshold corrections to the b-quark mass, via their effects on the neutralino relic density and through the SUSY contribution to the BR($b\to s γ$) which is sensitive to the CP phases. We present some specific models with large SUSY phases, which can accommodate the fermion electric dipole moment constraints and give a neutralino relic density in agreement with observations as well as with the b-$τ$ unification constraint. The possibility of achieving WMAP relic density constraints with full Yukawa unification is also explored.

hep-ph↗

arXiv2004

Effective Lagrangian for $\bar q\tilde q'_iχ^+_j$, $\bar q\tilde q'_iχ^0_j$ interactions and Fermionic Decays of the Squarks with CP Phases

The one loop corrected effective Lagrangian for the quark-squark-chargino and quark-squark-neutralino interactions is computed. The effective Lagrangian takes into account the loop corrections arising from the exchange of the gluinos, charginos, neutralinos, W, Z, the charged Higgs, and the neutral Higgs. We further analyze the squark decays into charginos and neutralinos and discuss the effect of the loop corrections on them. The analysis takes into account CP phases in the soft parameters. It is found that the loop corrections to the stop decay widths into chargino and neutralinos can be as much as thirty percent or even larger. Further, the stop decay widths show a strong dependence on the CP phases. These results are of relevance in the precision predictions of squark decays in the context of specific models of soft breaking in supergravity and string based models.

hep-ph↗

arXiv2004

Effective Lagrangian for Charged Higgs Couplings

The effective Lagrangian including one loop corrections is deduced for the couplings of the charged Higgs with quarks and leptons, and with charginos and neutralinos. The effect of the one loop corrections is found to be quite significant in a number of sectors. The effective Lagrangian is then used to analyze the decay of the charged Higgs into a number of decay channels. Specifically we consider the decay of $H^+(H^-)$ into the decay modes $t\bar b$ ($\bar t b$), $\barτν_τ$ ($τ\bar ν_τ$), and $χ_i^+χ_j^0(χ_i^-χ_j^0)$ (i=1,2; j=1-4). The loop corrections to these decay modes are also found to be quite significant lying in the range 20-30% in significant regions of the parameter space of the SUGRA model. The effects of CP phases on the effective Lagrangian and on the branching ratios are also analysed and these effects found to be important.

hep-ph↗

arXiv2004

MSUGRA Dark Matter and the b Quark Mass

We extend the commonly used mSUGRA framework to allow complex soft terms. We show how these phases can induce large changes of the SUSY threshold corrections to the b quark mass and affect the neutralino relic density predictions of the model. We present some specific models with large SUSY phases which can accommodate the fermion electric dipole moment constraints and a neutralino relic density within the WMAP bounds.

hep-ph↗

arXiv2004

Effective Lagrangian for $χ^+_iχ_j^0H^-$ Interaction in the MSSM and Charged Higgs Decays

We extend previous analyses of the supersymmetric loop correction to the charged Higgs couplings to include the coupling $H^{\pm}χ^{\mp}χ^0$. The analysis completes the previous analyses where similar corrections were computed for $H^+\bar t b$ ($H^-t\bar b$), and for $H^+τ^- \barν_τ$ ($H^- τ^+ ν_τ$) couplings within the minimal supersymmetric standard model. The effective one loop Lagrangian is then applied to the computation of the charged Higgs decays. The sizes of the supersymmetric loop correction on branching ratios of the charged Higgs $H^+(H^-)$ into the decay modes $t\bar b$ ($\bar t b$), $\barτν_τ$ ($τ\bar ν_τ$), and $χ_i^+χ_j^0(χ_i^-χ_j^0)$ (i=1,2; j=1-4) are investigated and the supersymmetric loop correction is found to be significant, i.e., in the range 20-30% in significant regions of the parameter space. The loop correction to the decay mode $χ_1^{\pm}χ_2^0$ is examined in specific detail as this decay mode leads to a trileptonic signal. The effects of CP phases on the branching ratio are also investigated. A brief discussion of the implications of the analysis for collders is given.

hep-ph↗

arXiv2004

Sensitivity of Supersymmetric Dark Matter to the b Quark Mass

An analysis of the sensitivity of supersymmetric dark matter to variations in the b quark mass is given. Specifically we study the effects on the neutralino relic abundance from supersymmetric loop corrections to the mass of the b quark. It is known that these loop corrections can become significant for large $\tanβ$. The analysis is carried out in the framework of mSUGRA and we focus on the region where the relic density constraints are satisfied by resonant annihilation through the s-channel Higgs poles. We extend the analysis to include CP phases taking into account the mixing of the CP-even and CP-odd Higgs boson states which play an important role in determining the relic density. Implications of the analysis for the neutralino relic density consistent with the recent WMAP relic density constraints are discussed.

hep-ph↗

arXiv2003

Weak Isospin Violations in Charged and Neutral Higgs Couplings from SUSY Loop Corrections

Supersymmetric QCD and supersymmetric electroweak loop corrections to the violations of weak isospin to Yukawa couplings are investigated. Specifically it involves an analysis of the supersymmetric loop corrections to the Higgs couplings to the third generation quarks and leptons. Here we analyze the SUSY loop corrections to the charged Higgs couplings which are then compared with the supersymmetric loop corrections to the neutral Higgs couplings previously computed. It is found that the weak isospin violations can be quite significant, i.e, as much as 40-50% or more of the total loop correction to the Yukawa coupling. The effects of CP phases are also studied and it is found that these effects can either enhance or suppress the weak isospin violations. We also investigate the weak isospin violation effects on the branching ratio $BR(H^-\to\bar t b)/ BR(H^-\to \barν_ττ^-)$ and show that the effects are sensitive to CP phases. Thus an accurate measurement of this branching ratio along with the branching ratio of the neutral Higgs boson decays can provide a measure of weak isospin violation along with providing a clue to the presence of supersymmetry.

hep-ph↗

arXiv2003

Corrections to b, t quark masses and $τ$ lepton mass in SUGRA including CP phases

A brief review is given of recent analyses of the effects of CP phases on the supersymmetric QCD and supersymmetric electroweak contibutions to the $b$ and $t$ quark masses and to the $τ$ lepton mass in SUGRA models. The effects of CP phases on the supersymmetric contributions are found to be significanlty large for the b quark mass as they can change both its sign and its magnitude. Thus with the inclusion of CP phases the supersymmetric correction to the b quark mass can be as much as fifty percent or more of the total b quark mass. For the case of the $τ$ lepton, the effects of CP phases on the supersymmetric correction is also relatively large as it can again affect both the sign and the magnitude of the $τ$ mass correction. However, in this case the overall correction is found to be only a few percent. The effect of CP phases on SUSY contribution to the $t$ quark mass was also investigated. However, in this case the overall correction is less than a percent with or without the inclusion of phases. These results have important implications for $b-τ$ unification and for $b-t-τ$ unification in the context of unified theories.

hep-ph↗

arXiv2003

Decays of Higgs to $b\bar b$, $τ\barτ$ and $c\bar c$ as Signatures of Supersymmetry and CP Phases

The branching ratio of the lightest Higgs decay into $b\bar b$, $τ\barτ$ and $c\bar c$ is sensitive to supersymmetric effects. We include in this work the effects of CP phases on the Higgs decays. Specifically we compute the deviation of the CP phase dependent branching ratio from the standard model result. The analysis includes the full one loop corrections of fermion masses including CP phases involving the gluino, the chargino and the neutralino exchanges. The analysis shows that the supersymmetric effects with CP phases can change the branching ratios by as much as 100% for the lightest Higgs decay into $b\bar b$ and $τ\barτ$ with similar results holding for the heavier Higgs decays. A detailed analysis is also given of the effects of CP phases on the Higgs decays into $c\bar c$. The deviations of $R_{b/τ}$ and $R_{b/c}$ from the standard model result are investigated as a possible signature of supersymmetry and CP effects. Thus a measurement of the decays of the higgs into $b\bar b$, $τ\bar τ$ and $c\bar c$ may provide important clues regarding the existence of supersymmetry and CP phases.

hep-ph↗

arXiv2003

SUSY QCD and SUSY Electroweak Loop Corrections to $b, t$ and $τ$ Masses Including the Effects of CP Phases

We compute supersymmetric QCD and supersymmetric electroweak corrections to the b and t quark masses and to the $τ$ lepton mass in the presence of CP phases valid for all $\tanβ$. The analysis includes one loop diagrams arising from the exchange of gluinos, charginos and neutralinos. We find that the CP effects can change both the magnitude as well as the sign of the supersymmetric loop correction. In the region of parameter space studied we found that the numerical size of the correction to the b quark mass can be as large as 30 percent and to the $τ$ lepton mass as much as 5 percent. For the top quark mass the correction is typically less than a percent. These corrections are of importance in unified models since $b-τ$ and $b-t-τ$ unification is strongly affected by the size of these corrections. More generally these results will be of importance in analyses of quark-lepton textures with the inclusion of CP phases. Further, the analysis presented here is relevant in a variety of low energy phenomena where supersymmetric QCD and supersymmetric electroweak corrections on b mass enter prominently in B physics, e.g., in processes such as $B^0_{s,d}\to l^+ł^-$.

hep-ph↗

arXiv2002

CP Violation Effects on $B^0_{s,d}\to \it l^+\it l^-$ in Supersymmetry at Large $\tanβ$

An analytic analysis of the CP violating effects arising from the soft SUSY breaking parameters on the decays $B^0_{s,d}\to \it l^+\it l^-$ at large $\tanβ$ is given. It is found that the phases have a strong effect on the branching ratio and in some regions of the parameter space they can lead to a variation of the branching ratio by as much as 1-2 orders of magnitude. These results have important implications for the discovery of the $B^0_{s}\to μ^+μ^-$ signal in RUNII of the Tevatron and further on how the parameter space of SUSY models will be limited once the signal is found.

hep-ph↗