arXiv subjects

Vladimir A. Kovalchuk

Publications and source records attributed to Vladimir A. Kovalchuk.

6 recordsLinked to original sources

arXiv2017

Decay of the Higgs boson to $τ^- τ^+$ and non-Hermiticity of the Yukawa interaction

The issue of Hermiticity of the Higgs boson interaction with fermions is addressed. A model for non-Hermitian Yukawa interaction is proposed and approximation of one fermion generation is considered. Symmetry properties of the corresponding $h f \bar{f}$ Lagrangian with respect to the discrete P, C and T transformations are analyzed, and the modified Dirac equation for the free fermion is studied. Longitudinal polarization of the fermions in the decay $h \to f \bar{f}$, which arises due to non-Hermiticity of the $h f \bar{f}$ interaction, is discussed. It is suggested to study effects of this non-Hermiticity in the decay $h \to τ^- τ^+ \to μ^- {\bar ν}_μν_τ\, μ^+ ν_μ{\bar ν}_τ$, for which observables (asymmetries) are constructed which take nonzero values for a non-Hermitian $h τ^- τ^+$ interaction. These asymmetries are analyzed for various configurations of the muon energies.

hep-ph↗

arXiv2014

Angular distribution and forward-backward asymmetry of the Higgs-boson decay to photon and lepton pair

The Higgs-boson decay h -> gamma l+ l- for various lepton states l = (e, mu, tau) is analyzed. The differential decay width and forward-backward asymmetry are calculated as functions of the dilepton invariant mass in a model where the Higgs boson interacts with leptons and quarks via a mixture of scalar and pseudoscalar couplings. These couplings are partly constrained from data on the decays to leptons, h -> l+ l-, and quarks h -> q \bar{q} (where q = (c, b)), while the Higgs couplings to the top quark are chosen from the two-photon and two-gluon decay rates. Nonzero values of the forward-backward asymmetry will manifest effects of new physics in the Higgs sector. The decay width and asymmetry integrated over the dilepton invariant mass are also presented.

hep-ph↗

arXiv2013

Polarization effects in the Higgs boson decay to gamma Z and test of CP and CPT symmetries

Polarization characteristics of gamma gamma and gamma Z states in the Higgs boson decays h -> gamma gamma and h -> gamma Z are discussed. Based on effective Lagrangian, describing h gamma gamma and h gamma Z interactions with CP-even and CP-odd parts, we calculate polarization parameters xi_1, xi_2, xi_3. A nonzero value of the photon circular polarization, defined by parameter xi_2, arises due to presence of both parts in effective Lagrangian and its non-Hermiticity. The circular polarization is proportional to the forward-backward asymmetry of fermions in the decay h -> gamma Z -> gamma f bar{f}. Measurement of this observable would allow one to search for deviation from the standard model and possible violation of CPT symmetry. We discuss also a possibility to measure parameters xi_1, xi_3, describing correlation of linear polarizations of photon and Z boson, in the decay h -> gamma* Z -> l+ l- Z via distribution over the azimuthal angle between the decay planes of gamma* -> l+ l- and Z -> f bar{f}. Deviation of the measured value of xi_1 from zero will indicate CP violation in the Higgs sector.

hep-ph↗

arXiv2012

Contribution of vector resonances to the {\bar B}_d^0 -> {\bar K}^{*0} mu^+ mu^- decay

The fully differential angular distribution for the rare flavor-changing neutral current decay \bar{B}_d^0 -> \bar{K}^{*0} (-> K- pi+) mu+ mu- is studied. The emphasis is placed on accurate treatment of the contribution from the processes \bar{B}_d^0 -> \bar{K}^{*0} (-> K- pi+) V with intermediate vector resonances V = rho(770), omega(782), phi(1020), J/psi, psi(2S), ... decaying into the mu+ mu- pair. The dilepton invariant-mass dependence of the branching ratio, longitudinal polarization fraction f_L of the \bar{K}^{*0} meson, and forward-backward asymmetry A_{FB} is calculated and compared with data from Belle, CDF and LHCb. It is shown that inclusion of the resonance contribution may considerably modify the branching ratio, calculated in the SM without resonances, even in the invariant-mass region far from the so-called charmonia cuts applied in the experimental analyses. This conclusion crucially depends on values of the unknown phases of the B^0 -> K^{*0} J/psi and B^0 -> K^{*0} psi(2S) decay amplitudes with zero helicity.

hep-ph↗

arXiv2011

Asymmetries in {\bar B}_d^0 -> {\bar K}^{*0} e+ e- decay and contribution of vector resonances

The fully differential angular distribution for the rare flavor-changing neutral current decay {\bar B}_d^0 -> {\bar K}^{*0} (-> K^- π^+) e+ e- is studied. The emphasis is placed on accurate treatment of the contribution from the processes \bar{B}_d^0 -> \bar{K}^{*0} (-> K^- pi^+) V with intermediate vector resonances V = ρ(770), ω(782), ϕ(1020), J/ψ, ψ(2S), ... decaying into the e+ e- pair. The two versions of the vector-meson-dominance model for the transition V γare used and tested. The present method of including vector resonances is also compared with the existing in the literature method. The electron-positron invariant mass dependence of the branching ratio and various asymmetries is calculated. The branching ratio, longitudinal polarization fraction of the {\bar K}^{*0} meson, transverse asymmetry A_T^{(2)} and forward-backward asymmetry are compared with data from Belle and CDF, and predictions for experiments at LHCb are made.

hep-ph↗

arXiv2010

Contribution of low-lying vector resonances to polarization observables in \bar B_d^0 -> \bar K*0 e+ e- decay

The branching ratio and other observables for the rare flavour-changing neutral current decay \bar B_d^0 -> \bar K*0 (-> K- pi+) e+ e- are studied below the \bar{c} c threshold. The total amplitude for this decay includes the term coming from the standard model effective Hamiltonian and the term generated by the processes \bar B_d^0 -> \bar K*0 (-> K- pi+) V with intermediate low-lying vector resonances V = rho(770), omega(782), phi(1020) decaying into the e+ e- pair. The resonance contribution to the branching ratio, polarization fractions of the K* meson and coefficients in the angular distribution is calculated. The influence of the resonances on the integrated observables in the region of electron-positron invariant mass up to 1 GeV is studied in view of the planned measurements of the photon polarization at the LHCb.

hep-ph↗