arXiv subjects

G. K. Yeghiyan

Publications and source records attributed to G. K. Yeghiyan.

8 recordsLinked to original sources

arXiv2007

On the Non-Manifest Left-Right Model Contribution to the Lifetime Difference in $D^0 - \bar{D}^0$ Mixing

New physics contribution to the lifetime difference in $D^0 - \bar{D}^0$ mixing is re-examined within the non-manifest Left-Right Symmetric Model. Diagrams with one of $ΔC = 1$ transitions, mediated by a propagator with $W_L - W_R$ mixing, are revisited. While these diagrams are believed to give the dominant contribution, compatible with the experimental data, it is shown that due to GIM cancelation, such diagrams are negligible in sum. Thus, Left-Right Symmetric Model contribution to the lifetime difference in $D^0 - \bar{D}^0$ mixing is about two orders of magnitude less than actual experimental value for $ΔΓ_D$.

hep-ph↗

arXiv2001

$O(α_s)$ Corrections to $B \to X_s e^+ e^-$ Decay in the 2HDM

$O(α_s)$ QCD corrections to the inclusive $B \to X_s e^+ e^-$ decay are investigated within the two - Higgs doublet extension of the standard model (2HDM). The analysis is performed in the so - called off-resonance region; the dependence of the obtained results on the choice of the renormalization scale is examined in details. It is shown that $O(α_s)$ corrections can suppress the $B \to X_s e^+ e^-$ decay width up to $1.5 ÷3$ times (depending on the choice of the dilepton invariant mass $s$ and the low - energy scale $μ$). As a result, in the experimentally allowed range of the parameters space, the relations between the $B \to X_s e^+ e^-$ branching ratio and the new physics parameters are strongly affected. It is found also that though the renormalization scale dependence of the $B \to X_s e^+ e^-$ branching is significantly reduced, higher order effects in the perturbation theory can still be nonnegligible.

hep-ph↗

arXiv2000

Direct CP-asymmetry in Inclusive Rare B-decays in 2HDM

The direct CP-asymmetry in the inclusive $B \to X_d γ$ and $B \to X_d e^+ e^ - $ decays is investigated in the two-Higgs doublet extension of the Standard Model (2HDM). The investigation is performed in the lowest non-vanishing order of the perturbation theory using the existing restrictions on the 2HDM parameters space. It is shown that the direct CP-asymmetry in the $B \to X_d γ$ decay can deviate significantly from the Standard Model predictions. In the presence of only one source of CP-violation (the CKM matrix weak phase) $a_{CP}(B \to X_d γ)$ can have the sign opposite to that in the SM. The new source of CP-violation can make $|a_{CP}(B \to X_d γ)|$ arbitrary small (unlike the SM case) and hence unmeasurable. Quantitatively, the obtained results suffer from the uncertainty of the choice of renormalization scale. As for the $B \to X_d e^+ e^ - $ rate asymmetry, its renormalization scale dependence in the lowest non-vanishing order does not allow to conclude if this quantity is efficient for testing New Physics beyond the Standard Model.

hep-ph↗

arXiv1999

Upper Bound on the Lightest Higgs Mass in Supersymmetric Theories

The problem of the lightest Higgs boson mass in the next-to-minimal supersymmetric standard model (NMSSM) is investigated. Assuming the validity of the perturbation theory up to unification scales and using the recent experimental results for the top quark mass, the restrictions on the NMSSM coupling constants are obtained. These restrictions are used to make the predictions for the lightest Higgs mass, which are compared to those of the minimal supersymmetric standard model (MSSM).

hep-ph↗

arXiv1999

Infrared Quasi Fixed Points and Mass Predictions in the MSSM

We consider the infrared quasi-fixed point solutions of the renormalization group equations for the top-quark Yukawa coupling and soft supersymmetry breaking parameters in the MSSM. The IR quasi-fixed points together with the values of the gauge couplings, the top-quark and Z-boson masses allow one to predict masses of the Higgs bosons, the stop squarks and the lightest chargino as functions of the only free parameter $m_{1/2}$ or the gluino mass. The mass of the lightest Higgs boson for $μ>0$ and $M_{SUSY} \approx 1$ TeV is found to be $m_h=(94.3+1.6+0.6\pm5\pm0.4)$ GeV. The case with $μ<0$ is excluded by experimental data.

hep-ph↗

arXiv1997

CP-Violation in b Quark Radiative Inclusive Decays

The direct CP-violations in $SU(2)_{L}\times SU(2)_{R} \times U(1)$ model and two-Higgs doublet extension of the standard model for $b \to dγ$ and $b \to sγ$ decays are investigated. The calculated value of CP-asymmetry for these two models and for $b \to dγ$ and $b \to sγ$ decays for the wide range of parameters may exceed the value, predicted by the standard model and has a sign opposite to that of the latter.

hep-ph↗

arXiv1996

Higgs Boson Masses in Supersymmetric Theories

The Higgs boson mass problem is considered in the next to minimal supersymmetric standard model. The Higgs potential and the renormalization group equations for the gauge, Yukawa and scalar coupling constants are analyzed. The restrictions for the Higgs boson masses are found for the cases of presence and absence of spontaneous CP- violation.

hep-ph↗

arXiv1996

Higgs Boson Masses in NMSSM with Spontaneous CP-violation

The Higgs boson mass problem is considered in the next-to-minimal supersymmetric standard model for the case of the spontaneous CP violation. The renormalization group equations for the gauge, Yukawa and scalar coupling constants, the effective Higgs potential and lower experimental bounds on Higgs boson and chargino masses are analyzed. The restrictions on the Higgs boson masses are found.

hep-ph↗