arXiv subjects

Artyom Hovhannisyan

Publications and source records attributed to Artyom Hovhannisyan.

5 recordsLinked to original sources

arXiv2026

Decay matrix of B-\bar{B} mixing: Mixing of dimension-seven operators into dimension-six operators under renormalization

The precise measurement of the width difference ΔΓ_s among the mass eigenstates of the B_s-\bar{B}_s system requires the calculation of the corresponding decay matrix to order α_s/m_b. QCD corrections to power-suppressed terms in the Heavy Quark Expansion involve the renormalization of dimension-7 four-quark operators for which no general methodology is available yet. In the \overline{MS} scheme one-loop corrections to matrix elements of dimension-7 operators violate the power counting, but we find the responsible terms to be infrared-finite and show that they can be absorbed into finite counterterms proportional to dimension-6 operators. We calculate all these counterterms and subsequently verify the consistency of our results with hadronic matrix elements calculated in the limit of a large number N_c of colours. The condition of correct power counting implies constraints on the possible definitions of evanescent operators.

hep-ph↗

arXiv2022

Addendum: Towards next-to-next-to-leading-log accuracy for the width difference in the $\mathbf{B_s-\bar{B}_s}$ system: fermionic contributions to order $\mathbf{(m_c/m_b)^0}$ and $\mathbf{(m_c/m_b)^1}$

We calculate the three-loop master integrals of Ref. [1] [arXiv:1709.02160] in analytic form. This allows us to present the fermionic contributions to the $ΔB=2$ Wilson coefficients of the $B$-$\bar B$ decay matrix in next-to-next-to-leading order of QCD with full analytic dependence on the mass of the charm quark in the fermionic loops.

hep-ph↗

arXiv2020

Penguin contribution to width difference and CP asymmetry in $B_q$-$\bar B_q$ mixing at order $α_s^2 N_f$

We present new contributions to the decay matrix element $Γ_{12}^q$ of the $B_q$-$\bar B_q$ mixing complex, where $q=d$ or $s$. Our new results constitute the order $α_s^2 N_f$ corrections to the penguin contributions to the Wilson coefficients entering $Γ_{12}^q$ with full dependence on the charm quark mass. This is the first step towards the prediction of the CP asymmetry $a_{\rm fs}^q$ quantifying CP violation in mixing at next-to-next-to-leading logarithmic order (NNLO) in quantum chromodynamics (QCD) and further improves the prediction of the width difference $ΔΓ_q$ between the two neutral-meson eigenstates. We find a sizable effect from the non-zero charm mass and our partial NNLO result decreases the NLO penguin corrections to $a_{\rm fs}^q$ by 37\% and those to $ΔΓ_q$ by 16\%. We further update the Standard-Model NLO predictions for $a_{\rm fs}^q$ and the ratio of the width and mass differences of the $B_q$ eigenstates: If we express the results in terms of the pole mass of the bottom quark we find $a_{\rm fs}^s=(2.07 \pm 0.10)\cdot 10^{-5}$, $a_{\rm fs}^d=(-4.71 \pm 0.24)\cdot 10^{-4}$, $ΔΓ_s/Δ{M}_s = (4.33 \pm 1.26)\cdot 10^{-3}$, and $ΔΓ_d/Δ{M}_d = (4.48 \pm 1.19)\cdot 10^{-3}$. In the $\overline{\rm MS}$ scheme these numbers read $a^s_{\rm fs} =(2.04 \pm 0.11)\cdot 10^{-5}$, $a^d_{\rm fs} = (-4.64 \pm 0.25)\cdot 10^{-4}$, $ΔΓ_s/Δ{M}_s = (4.97 \pm 1.02)\cdot 10^{-3}$, and $ΔΓ_d/Δ{M}_d = (5.07 \pm 0.96)\cdot 10^{-3}$.

hep-ph↗

arXiv2017

Towards next-to-next-to-leading-log accuracy for the width difference in the $B_s-\bar{B}_s$ system: fermionic contributions to order $(m_c/m_b)^0$ and $(m_c/m_b)^1$

We calculate a class of three-loop Feynman diagrams which contribute to the next-to-next-to-leading logarithmic approximation for the width difference $ΔΓ_{s}$ in the $B_s-\bar{B}_s$ system. The considered diagrams contain a closed fermion loop in a gluon propagator and constitute the order $α_s^2 N_f$, where $N_f$ is the number of light quarks. Our results entail a considerable correction in that order, if $ΔΓ_{s}$ is expressed in terms of the pole mass of the bottom quark. If the $\overline{MS}$ scheme is used instead, the correction is much smaller. As a result, we find a decrease of the scheme dependence. Our result also indicates that the usually quoted value of the NLO renormalization scale dependence underestimates the perturbative error.

hep-ph↗

arXiv2007

$B\to K^*\ell^+\ell^-$ Forward-backward Asymmetry and New Physics

The forward-backward asymmetry ${\cal A}_{\rm FB}$ in $B\to K^*\ell^+\ell^-$ decay is a sensitive probe of New Physics. Previous studies have focused on the sensitivity in the position of the zero. However, the short distance effective couplings are in principle complex, as illustrated by $B\to ρ\ell^+\ell^-$ decay within the Standard Model. Allowing the effective couplings to be complex, but keeping the $B\to K^*γ$ and $K^*\ell^+\ell^-$ rate constraints, we find the landscape for ${\cal A}_{\rm FB}(B\to K^*\ell^+\ell^-)$ to be far richer than from entertaining just sign flips, which can be explored by future high statistics experiments.

hep-ph↗