arXiv subjects

H. M. Asatrian

Publications and source records attributed to H. M. Asatrian.

30 records · Page 2Linked to original sources

arXiv2002

NNLL corrections to the angular distribution and to the forward-backward asymmetries in b -> X_s l+ l-

We present NNLL results for the double differential decay width dGamma(b -> X_s l+ l-)/(dsh dcos(theta)), where theta is the angle between the momenta of the b-quark and the l+, measured in the rest-frame of the lepton pair. From these results we also derive NNLL results for the lepton forward-backward asymmetries. Genuinely new calculations for the combined virtual- and gluon bremsstrahlung corrections associated with the operators O_7, O_9 and O_10 are necessary. We find that the NNLL corrections drastically reduce the renormalization scale dependence of the forward-backward asymmetries. In particular, sh_0, the position at which the forward-backward asymmetries vanish, is essentially free of uncertainties due to the renormalization scale at NNLL precision. We find sh_0(NNLL)=0.162 +/- 0.005, where the error is dominated by the uncertainty in (m_c/m_b). This is to be compared with sh_0(NLL)=0.144 +/- 0.020, where the error is dominated by uncertainties due to the choice of mu.

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arXiv2002

Complete gluon bremsstrahlung corrections to the process b -> s l+ l-

In a recent paper, we presented the calculation of the order (alpha_s) virtual corrections to b->s l+ l- and of those bremsstrahlung terms which are needed to cancel the infrared divergences. In the present paper we work out the remaining order(alpha_s) bremsstrahlung corrections to b->s l+ l- which do not suffer from infrared and collinear singularities. These new contributions turn out to be small numerically. In addition, we also investigate the impact of the definition of the charm quark mass on the numerical results.

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arXiv2002

Calculation of two-loop virtual corrections to b --> s l+ l- in the standard model

We present in detail the calculation of the virtual O(alpha_s) corrections to the inclusive semi-leptonic rare decay b --> s l+ l-. We also include those O(alpha_s) bremsstrahlung contributions which cancel the infrared and mass singularities showing up in the virtual corrections. In order to avoid large resonant contributions, we restrict the invariant mass squared s of the lepton pair to the range 0.05 < s/mb^2 < 0.25. The analytic results are represented as expansions in the small parameters s/mb^2, z = mc^2/mb^2 and s/(4 mc^2). The new contributions drastically reduce the renormalization scale dependence of the decay spectrum. For the corresponding branching ratio (restricted to the above s-range) the renormalization scale uncertainty gets reduced from +/-13% to +/-6.5%.

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arXiv2001

Two-loop virtual corrections to B --> X_s l^+ l^- in the standard model

We calculate O(alpha_s) two-loop virtual corrections to the differential decay width dGamma(B --> X_s l^+ l^-)/ds, where s is the invariant mass squared of the lepton pair. We also include those contributions from gluon bremsstrahlung which are needed to cancel infrared and collinear singularities present in the virtual corrections. Our calculation is restricted to the range 0.05 < s/m_b^2 < 0.25 where the effects from resonances are small. The new contributions drastically reduce the renormalization scale dependence of existing results for dGamma(B --> X_s l^+ l^-)/ds. For the corresponding branching ratio (restricted to the above s-range) the renormalization scale uncertainty gets reduced from +/- 13% to +/- 6.5%.

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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.

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arXiv1999

CP Asymmetry for Inclusive Decay $B \to X_d + γ$ in the Minimal Supersymmetric Standard Model

We study the inclusive rare decay $B\to X_d+γ$ in the supergravity inspired Minimal Supersymmetric Standard Model and compute the CP-asymmetry in the decay rates. We show that there exist two phenomenologically acceptable sets of SUSY parameters: for one set the CP-asymmetry has the same (positive) sign as in the Standard Model and lies in the range (5-45)% while for the other set it is negative with values within -(2-21)%.

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arXiv1999

NLL Corrections for B-Meson Radiative Exclusive Decays

We calculate the next-to-leading corrections to the branching ratio of exclusive $B\to K^* γ$ decay. The renormalization scale dependence is reduced compared to the leading logarithmic result but there remains a dependence on a cutoff parameter of the hadronic model. The calculated corrections increase the predicted branching ratio by about 10%, but it remains in agreement with the experimental value.

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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.

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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.

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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.

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arXiv1995

The Neutrino Masses in SUSY GUT

The neutrino mass problem in $SU(4) \times SU(2)_{L} \times SU(2)_{R}$ SUSY GUT obtained from the compactification of $E_{8} \times E_{8}$ heterotic string is analyzed. The estimated values of the neutrino masses and mixing angles can explain the experimental data on solar neutrino flux.

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arXiv1995

Heavy Majorana Neutrino Decays and CP-Parity Violation

In the framework of the left-right symmetric model the CP-parity violation has been studied in heavy Majorana neutrino decays $N\rightarrow e^{\mp} μ^{\pm} n$. The numerical estimates of CP-asymmetry for different masses of neutrino and $W_{R}^{\pm}$-boson were obtained. The possibility to detect this phenomenon at high energy colliders is mentioned.

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