Searcharxiv⌕ Search

arXiv subjects

Mikhail A. Ivanov

Publications and source records attributed to Mikhail A. Ivanov.

At least 73 records · Page 4Linked to original sources
arXiv2015

Physical observables in the decay $Λ_b \to Λ_c (\to Λ+π)+τ^{-}+\bar ν_τ$

We analyze the tauonic semileptonic baryon decays $Λ^0_b \to Λ^+_c + τ^{-} +\bar ν_τ$ with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the $Λ^+_c$ and the $τ^-$, and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.

hep-ph↗
arXiv2015

Pion polarizabilities: Theory vs Experiment

The values of charged pion polarizabilities obtained in the framework of chiral perturbation theory at the level of two-loop accuracy are compared with the experimental result recently reported by COMPASS Collaboration. It is found that the calculated value for the dipole polarizabilities $(α-β)_{π^\pm}= (5.7\pm 1.0)\times 10^{-4}\,{\rm fm}^3$ fits quite well the experimental result $(α-β)_{π^\pm} = (4.0 \pm 1.2_{\rm stat} \pm 1.4_{\rm syst}) \times 10^{-4}\,{\rm fm}^3$.

hep-ph↗
arXiv2015

On Chow weight structures for $cdh$-motives with integral coefficients

The main goal of this paper is to define a certain Chow weight structure $w_{Chow}$ on the category $DM_c(S)$ of (constructible) $cdh$-motives over an equicharacteristic scheme $S$. In contrast to the previous papers of D. Hébert and the first author on weights for relative motives (with rational coefficients), we can achieve our goal for motives with integral coefficients (if $\operatorname{char}S=0$; if $\operatorname{char}S=p>0$ then we consider motives with $\mathbb{Z}[\frac{1}{p}]$-coefficients). We prove that the properties of the Chow weight structures that were previously established for $\mathbb{Q}$-linear motives can be carried over to this "integral" context (and we generalize some of them using certain new methods). In this paper we mostly study the version of $w_{Chow}$ defined via "gluing from strata"; this enables us to define Chow weight structures for a wide class of base schemes. As a consequence, we certainly obtain certain (Chow)-weight spectral sequences and filtrations for any (co)homology of motives.

math.AG↗
arXiv2015

The semileptonic decay Lambda_b -> Lambda_c + tau(-) + antinu_tau in the covariant confined quark model

Recently there has been much interest in the tauonic semileptonic meson decays B -> D + tau + nu_tau and B -> D* + tau + nu_tau where one has found larger rates than what is predicted by the Standard Model. We analyze the corresponding semileptonic baryon decays Lambda_b(0) -> Lambda_c(+) + tau(-) + antinu_tau with particular emphasis on the lepton helicity flip and scalar contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization of the daughter baryon Lambda_c(+) and the tau-lepton, and the lepton-side forward-backward asymmetries. The nonvanishing polarization of the daughter baryon Lambda_c(+) leads to hadron-side asymmetries in e.g. the decay Lambda_c(+) -> Lambda(0) + pi(+) and azimuthal correlations between the two final state decay planes which we specify. We provide numerical results on these observables using results of the covariant confined quark model. We find large lepton mass effects in the q2-spectra and in the polarization observables.

hep-ph↗
arXiv2015

Form factors of the B-S-transitions in the covariant quark model

In the wake of exploring uncertainty in the full angular distribution of the $B\to Kπ+μ^+μ^-$ caused by the presence of the intermediate scalar $K^\ast_0$ meson, we perform the straightforward calculation of the $B(B_s)\to S$ (S is a scalar meson) transition form factors in the full kinematical region within the covariant quark model. We restrict ourselves by the scalar mesons below 1 GeV: $a_0(980), f_0(500), f_0(980), K^\ast_0(800)$. As an application of the obtained results we calculate the widths of the semileptonic and rare decays $B(B_s)\to S\ell\barν$, $B(B_s)\to S\ell\bar\ell$ and $B(B_s)\to Sν\barν$. We compare our results with those obtained in other approaches.

hep-ph↗
arXiv2014

On the meson mass spectrum in the covariant confined quark model

We provide a new insight into the problem of generating the hadron mass spectrum in the framework of the covariant confined quark model. One of the underlying principles of this model is the compositeness condition which means that the wave function renormalization constant of the elementary hadron is equal to zero. In particular, this equation allows to express the Yukawa coupling of the meson fields to the constituent quarks as a function of other model parameters. In addition to the compositeness condition we also employ a further equation which relates the meson mass function to the Fermi coupling. Both equations guarantee that the Yukawa-type theory is equivalent to the Fermi-type theory thereby providing an interpretation of the meson field as the bound state of its constituent fermions (quarks). We evaluate the Fermi-coupling as a function of meson (pseudoscalar and vector) masses and vary the values of the masses in such a way to obtain a smooth behavior for the resulting curve. The mass spectrum obtained in this manner is found to be in good agreement with the experimental data. We also compare the behavior of our Fermi-coupling with the strong QCD coupling alpha_s calculated in an QCD-inspired approach.

hep-ph↗
arXiv2013

Polarization effects in the cascade decay Lambda_b -> Lambda(-> p pi-) + J/psi(-> l+ l-) in the covariant confined quark model

We calculate the invariant and helicity amplitudes for the nonleptonic decay Lambda_b -> Lambda + J/psi, psi(2S) in the covariant confined quark model. We discuss joint angular decay distributions in the cascade decay Lambda_b -> Lambda(-> p pi-) + J/psi, psi(2S) (-> l+ l-) and calculate some of the asymmetry parameters that characterize the joint angular decay distribution. We confirm expectations from the naive quark model that the transitions into the lambda_Lambda=1/2 helicity states of the daughter baryon Lambda are strongly suppressed leading to a near maximal negative polarization of the Lambda. For the same reason the azimuthal correlation between the two decay planes spanned by (p pi-) and (l+ l-) is negligibly small. We provide form factor results for the whole accessible q2-range. Our results are close to lattice results at minimum recoil and light-cone sum rule results at maximum recoil. A new feature of our analysis is that we include lepton mass effects in the calculation which allows us to also describe the cascade decay Lambda_b -> Lambda(-> p pi-) + psi(2S)(-> tau+ tau-).

hep-ph↗
arXiv2013

Rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma : Differential and total rates, lepton- and hadron-side forward-backward asymmetries

Using the covariant constituent quark model previously developed by us we calculate the differential rate and the forward-backward asymmetries on the lepton and hadron side for the rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma. We use helicity methods to write down a three-fold joint angular decay distribution for the cascade decay Lambda_b -> Lambda (-> p pi-) + J_eff (-> l+ l-). Through appropriate angular integrations we obtain expressions for the rates, the lepton-side forward-backward (FB) asymmetry and the polarization of the daughter baryon Lambda leading to a hadron-side forward-backward asymmetry. We present numerical results on these observables using the covariant quark model and compare our results to the results of other calculations that have appeared in the literature.

hep-ph↗
arXiv2013

Decays $B_{s}\rightarrow J/ψ+η$ and $B_{s}\rightarrow J/ψ+η'$ in the framework of covariant quark model

The covariant quark model represents an appropriate theoretical framework to describe the recent results on $B_{s}\rightarrow J/ψ+η$ and $B_{s}\rightarrow J/ψ+η'$ decays from the Belle collaboration. In this article we present the main features of he covariant quark model together with details on some of its aspects and methods, which we consider to be important. Further we apply the model specifically to the studied decay processes and give numerical results on decay widths as they follow from the odel. We conclude that the model, with most of its parameters previously fixed from different processes, is able to incorporate the new measurements from the Belle experiment.

hep-ph↗
arXiv2013

Multiquark states in the covariant quark confinement model

This talk reviews the last applications of the covariant quark model for studying the properties of the multiquark states: B_s-meson (quark-antiquark state), light baryons (three-quark states) and tetraquark (four-quark state). The form factors of the B(B_s)-> P(V)-transitions are evaluated in the full kinematical region of momentum transfer squared. The widths of some B_s-nonleptonic decays are calculated. The static properties of the proton and neutron, and the Λ-hyperon (magnetic moments and charge radii) and the behavior of the nucleon form factors at low momentum transfers are described. The consequences of treating the X(3872) meson as a tetraquark bound state are explored. The decay widths of the observed channels X->J/ψ+2π(3π) and X-> \bar D^0 + D^0+π^0 via the intermediate off--shell states X-> J/ψ+ρ(ω) and X-> \bar D + D^* are calculated. Its one-photon decay X-> γ+ J/ψis also analyzed.

hep-ph↗
arXiv2012

Light baryons and their electromagnetic interactions in the covariant constituent quark model

We extend the confined covariant constituent quark model that was previously developed by us for mesons to the baryon sector. In our numerical calculation we use the same values for the constituent quark masses and the infrared cutoff as have been previously used in the meson sector. In a first application we describe the static properties of the proton and neutron, and the $Λ$-hyperon (magnetic moments and charge radii) and the behavior of the nucleon form factors at low momentum transfers. We discuss in some detail the conservation of gauge invariance of the electromagnetic transition matrix elements in the presence of a nonlocal coupling of the baryons to the three constituent quark fields.

hep-ph↗
arXiv2012

Form factors for semileptonic, nonleptonic and rare $B\, (B_s)$ meson decays

We provide new values for the model parameters of the covariant constituent quark model (with built--in infrared confinement) in the meson sector by a fit to the leptonic decay constants and a number of electromagnetic decays. We then evaluate, in a parameter free way, the form factors of the $B(B_s)\to P(V)$-transitions in the full kinematical region of momentum transfer. As an application of our results we calculate the widths of the nonleptonic $B_s$-decays into $D_s^- D_s^+,$ $D_s^{\ast\,-} D_s^{+}+D_s^- D_s^{\ast\,+}$ and $D_s^{\ast\,-} D_s^{\ast\,+}$. These modes give the largest contribution to $ΔΓ$ for the $B_s-\bar B_s$ system. We also treat the nonleptonic decay $B_{s}\to\Jpsiϕ$. Although this mode is color suppressed this decay has important implications for the search of possible CP-violating New Physics effects in $B_s-\bar B_s$ mixing.

hep-ph↗
arXiv2012

Heavy-quark symmetries in the light of nonperturbative QCD approaches

We critically review the validity of heavy-quark spin and flavor symmetries in heavy-light decay constants, form factors and effective couplings obtained within a nonperturbative framework, the ingredients of which are all motivated by Dyson-Schwinger equations studies of QCD. Along the way, we make new predictions for two effective nonphysical couplings: g_{DsDK} = 24.1+2.5/-1.6 and g_{BsBK} = 33.3+4.0/-3.7.

nucl-th↗
arXiv2011

Integrating out the heaviest quark in N--flavour ChPT

We extend a known method to integrate out the strange quark in three flavour chiral perturbation theory to the context of an arbitrary number of flavours. As an application, we present the explicit formulae to one--loop accuracy for the heavy quark mass dependency of the low energy constants after decreasing the number of flavours by one while integrating out the heaviest quark in N--flavour chiral perturbation theory.

hep-ph↗
arXiv2011

One-photon decay of the tetraquark state $X(3872) \to γ+ J/ψ$ in a relativistic constituent quark model with infrared confinement

We further explore the consequences of treating the X(3872) meson as a tetraquark bound state by analyzing its one-photon decay X => γ+ J/psi in the framework of our approach developed in previous papers which incorporates quark confinement in an effective way. To introduce electromagnetism we gauge a nonlocal effective Lagrangian describing the interaction of the X(3872) meson with its four constituent quarks by using the P-exponential path-independent formalism. We calculate the matrix element of the transition X => γ+ J/psi and prove its gauge invariance. We evaluate the X=> γ+ J/psi decay width and the longitudinal/transverse composition of the J/psi in this decay. For a reasonable value of the size parameter of the X(3872) meson we find consistency with the available experimental data. We also calculate the helicity and multipole amplitudes of the process, and describe how they can be obtained from the covariant transition amplitude by covariant projection.

hep-ph↗
arXiv2010

Strong D* -> D+pi and B* -> B+pi couplings

We compute g_{D* D pi} and g_{B* B pi} using a framework in which all elements are constrained by Dyson-Schwinger equation studies of QCD, and therefore incorporates a consistent, direct and simultaneous description of light- and heavy-quarks and the states they may constitute. We link these couplings with the heavy-light-meson leptonic decay constants, and thereby obtain g_{D* D pi}=15.9+2.1/-1.0 and g_{B* B pi}=30.0+3.2/-1.4. From the latter we infer \hat-g_B=0.37+0.04/-0.02. A comparison between g_{D* D pi} and g_{B* B pi} indicates that when the c-quark is a system's heaviest constituent, Lambda_{QCD}/m_c-corrections are not under good control.

nucl-th↗
arXiv2010

A relativistic quark model with infrared confinement and the tetraquark state

We explore the consequences of treating the X(3872) meson as a tetraquark bound state. As dynamical framework we employ a relativistic constituent quark model which includes infrared confinement in an effective way. We calculate the hadronic decay widths of the observed channels. For reasonable values of the size parameter of the X(3872) we find consistency with the available experimental data.

hep-ph↗