arXiv subjects

M. B. Voloshin

Publications and source records attributed to M. B. Voloshin.

At least 127 records · Page 7Linked to original sources

arXiv1999

Reducing model dependence of spectator effects in inclusive decays of heavy baryons

The dependence of inclusive weak decay rates of heavy hadrons on light spectator quarks is considered. The analysis of a previous work on relating the effects in b baryons to those in charmed baryons is extended to explicit evaluation of the matrix elements of certain four-quark operators over heavy baryons. It is shown that the usually postulated color antisymmetry of these matrix elements is significantly broken. The flavor-singlet shift of inclusive decay rates of b baryons due to the spectator effects is shown to be strongly suppressed in the leading-log approximation. Combined with the results for the flavor non-singlet splittings, this observation allows to argue, in a less model-dependent way, than before, that within the present understanding of the spectator effects it is highly unlikely that the lifetimes of the Lambda_b and the B_d can be split by more than 10%.

hep-ph↗

arXiv1999

Relations between inclusive decay rates of heavy baryons

The dependence of inclusive weak decay rates of heavy hadrons on the flavors of spectator light quarks is revisited with application to decays of charmed and b hyperons. It is pointed out that the differences in the semileptonic decay rates, the differences in the Cabibbo suppressed decay rates of the charmed hyperons, and the splitting of the total decay rates of the b hyperons are all related to the differences in the lifetimes of the charmed hyperons independently of poor knowledge of hadronic matrix elements. The approximations used in these relations are the applicability of the expansion in the inverse of the charmed quark mass and the flavor SU(3) symmetry.

hep-ph↗

arXiv1998

On intersection of domain walls in a supersymmetric model

We consider a classical field configuration, corresponding to intersection of two domain walls in a supersymmetric model, where the field profile for two parallel walls at a finite separation is known explicitly. An approximation to the solution for intersecting walls is constructed for a small angle at the intersection. We find a finite effective length of the intersection region and also an energy, associated with the intersection.

hep-th↗

arXiv1998

Isotopic splittings and OPE in B -> D semileptonic decays

It is shown that the kinematical difference in the decays B^- -> D^0 \ell \tilde νand B^0 -> D^+ \ell \tilde νdue to the isotopic mass splittings of the B and D mesons is compensated in the total decay rate by an appropriate difference in the lepton spectra. Thus there is no effect on the total decay rates in the linear order in the isotopic mass splittings, as required by the general consideration based on the operator product expansion. Although phenomenologically the isotopic difference in the spectra amounts to at most about 1%, in the theoretical aspect this effect can be viewed as an additional illustration of how the general OPE results emerge from the properties of exclusive channels.

hep-ph↗

arXiv1998

Top quark longitudinal polarization near the threshold in l+ l- annihilation

We show that the longitudinal polarization of the top quarks produced in the annihilation of e+ e- or mu+ mu- into tbar t at energies near the threshold is not affected by the large Coulomb-type corrections, which greatly modify the total cross section. Thus the longitudinal polarization, although small, may provide an independent information on the mass and the width of the top quark, largely independent of the uncertainty in alpha_s.

hep-ph↗

arXiv1997

Degenerate Domain Wall Solutions in Supersymmetric Theories

A family of degenerate domain wall configurations, partially preserving supersymmetry, is discussed in a generalized Wess-Zumino model with two scalar superfields. We establish some general features inherent to the models with continuously degenerate domain walls. For instance, for purely real trajectories additional "integrals of motion" exist. The solution for the profile of the scalar fields for any wall belonging to the family is found in quadratures for arbitrary ratio of the coupling constants. For a special value of this ratio the solution family is obtained explicitly in terms of elementary functions. We also discuss the threshold amplitudes for multiparticle production generated by these solutions. New unexpected nullifications of the threshold amplitudes are found.

hep-th↗

arXiv1997

On domain shapes and processes in supersymmetric theories

A supersymmetric theory with several scalar superfields generically has several domain wall type classical configurations which interpolate between various supersymmetric vacua of the scalar fields. Depending on the couplings, some of these configurations develop instability and decay into multiple domain walls, others can form intersections in space. These phenomena are considered here in a simplest, yet non-trivial, model with two scalar superfields.

hep-th↗

arXiv1997

On the Feasibility of Low-Background Ge-NaI Spectrometer for Neutrino Magnetic Moment Measurement

We analyze the possibility of using a low-background Ge-NaI spectrometer in a reactor experiment for a search for neutrino magnetic moment down to $3 \times 10^{-11}$ of the electron magneton. The properties of the so-far existing Ge low-background spectrometers are discussed and additional sources of background in a reactor experiment at a small depth are estimated. These estimates place specific requirements on the design of the spectrometer. The results of preliminary background measurements at a small depth of 5 m.w.e. with a dedicated spectrometer built in ITEP are reported.

hep-ex↗

arXiv1997

Bound on V+A admixture in the b -> c current from inclusive vs. exclusive semileptonic decays of B mesons

An admixture of a right-handed $b \to c$ current in the semileptonic weak decays of the $B$ mesons would give a significantly different contribution to the inclusive rate of the decays $B \to l νX_c$ as compared to the exclusive decay $B \to D^* l ν$ at zero recoil. Thus a difference in the values of $|V_{cb}|$ extracted from the data on these two types of decay would measure such admixture. The present marginal mismatch in determination of $|V_{cb}|$ by the two methods can be interpreted as corresponding to $g_R/g_L \approx 0.14 \pm 0.18$.

hep-ph↗

arXiv1997

$O(m_c^{-2})$ nonperturbative corrections to the inclusive rate of the decay $B \to X_s γ$

It is shown that the inclusive rate of the rare weak radiative decays $B \to X_s γ$ contains a series of nonperturbative corrections, whose `short distance' scale is set by $m_c^{-1}$, rather than by $m_b^{- 1}$. The first correction in this series is expressed through the chromomagnetic interaction of the $b$ quark inside the $B$ meson and the relative magnitude of the effect is determined by the ratio $< {\overline B} | \bar b σ\cdot G b | B > / m_c^2$. Though the magnitude of this first correction is suppressed by a numerical coefficient, the sensitivity of the decay rate to the distance scale $m_c^{-1}$ may significantly limit the accuracy of purely perturbative predictions for the rate.

hep-ph↗

arXiv1996

Domain Walls are Diamagnetic

It is shown that contrary to a recent claim in the literature, the domain walls made of scalar field are diamagnetic due to presence of massless fermionic modes on the wall. The diamagnetism vanishes at high temperature. Thus the domain walls could produce no effect on a primordial magnetic field in the early universe.

hep-ph↗

arXiv1996

Spectator effects in semileptonic decay of charmed baryons

It is shown that the absolute rate of the semileptonic decays of the $Ξ_c$ baryons can be as much as two times higher than the semileptonic decay rate of $Λ_c$ due to the Pauli interference of the strange quark. This interference effect is still larger in the semileptonic decay rate of $Ω_c$. An experimental measurement of the difference of these rates would thus provide an important piece of information on the spectator effects in decays of hadrons containing a heavy quark.

hep-ph↗

arXiv1996

Second order QCD corrections to the nonleptonic decay of the $b$ quark in the slow charm limit

The perturbative QCD corrections to the nonleptonic decay rate of the $b$ quark are discussed. By considering the limit where the final charmed quarks are slow, it is argued that the coefficients of the $α_s^2$ terms, corresponding to next-to-next-to-leading order in the standard renormalization group expansion in $\ln (m_W/m_b)$, are naturally large. The large coefficients arise from the final-state gluon exchange between quarks and are associated with the region of rather low momenta, which may further enhance the phenomenological significance of these terms.

hep-ph↗

arXiv1995

How strong can the coupling of leptonic photons be?

Consequences of possible existence of leptonic photon are considered for a range of values of leptonic charge. In the case of a strong Coulomb-like leptonic repulsion between electrons the existence of ordinary condensed matter is impossible: antineutrinos cannot neutralize this destructive repulsion. The upper limit of leptonic charge is inferred from the Eötvös type experiments. If however there exist light stable scalar bosons with leptonic charge (e.g. singlet antisneutrinos) they may neutralize the electron repulsion. Possible experimental manifestations of such leptonic bosons in gases and condensed matter are briefly discussed.

hep-ph↗

arXiv1995

Precision determination of $α_s$ and $m_b$ from QCD sum rules for $b \overline b$.

The QCD sum rules for moments of production cross section of $b \overline b$ states in $e^+\,e^-$ annihilation are extremely sensitive to the values of $m_b$ and $α_s$ for moments of large order $n$. This enables one to extract from the existing data on $Υ$ resonances the values of these parameters with a high precision by using a non-relativistic expansion in $1/n$. It is found that the sum rules fit the data with $α_s^{\overline {MS}} (1 \, GeV) = 0.336 \pm 0.011$ and $m_b=4827 \pm 7 MeV$, where the estimate of the errors includes the theoretical uncertainty due to subleading in $1/n$ terms and the experimental uncertainty of the $e^+\,e^-$ annihilation cross section above the $B \overline B$ threshold. The found value of $α_s$, when evolved in two loops up to the $Z$ mass, gives $α_s^{\overline {MS}} (M_Z) = 0.109 \pm 0.001$. The $b$ quark mass $m_b$ corresponds to the `on shell' value appropriate for one-loop perturbative calculations.

hep-ph↗

arXiv1994

QCD radiative enhancement of the decay b -> c cbar s

A substantial enhancement is found of the $b \to c\,{\overline c}\, s$ decay rate due to the QCD interaction within the $\overline c s$ pair, which enhancement may amount to 30\%, or more. Some general features of calculation of the QCD radiative corrections in two first orders are discussed.

hep-ph↗

arXiv1994

Non-perturbative methods

The current theoretical understanding of processes involving many weakly interacting bosons in the Standard Model and in model theories is discussed. In particular, such processes are associated with the baryon and lepton number violation in the Standard Model. The most interesting domain where the multiplicity of bosons is larger than the inverse of small coupling constant is beyond the scope of perturbation theory and requires a non-perturbative analysis.

hep-ph↗

arXiv1994

Normalization of QCD corrections in top quark decay

We discuss the effects of QCD corrections to the on-shell decay $t \to b W$. We resolve the scale ambiguity using the Brodsky-Lepage-Mackenzie scheme, and find that the appropriate coupling constant is $α_{s}^{ \overline{MS}} (0.122m_{t})$. The largest long distance contribution comes from the definition of the on-shell mass of the top quark. We note that QCD corrections to the electroweak $ρ$ parameter are extremely small when the $ρ$ parameter is expressed in terms of the top quark width.

hep-ph↗