arXiv subjects

M. B. Voloshin

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

At least 109 records · Page 6Linked to original sources

arXiv2003

The photon spectrum in orthopositronium decay at ω_γ<< m_e

A closed analytic expression is given for the spectrum of low energy photons in the annihilation of orthopositronium, which expression sums all the effects of the Coulomb interaction between the electron and the positron. The applicability of the formula is limited only by the condition $ω_γ\ll m_e$. In the region $ω_γ\gg m_e α^2$ the Coulomb interaction term gives the leading at low energy one-loop correction, proportional to $α\sqrt{m_e/ω_γ}$, to the decay spectrum. The constant in $ω_γ$ radiative term in the one-loop correction to the spectrum is also presented here in an analytic form.

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arXiv2003

Interference and binding effects in decays of possible molecular component of X(3872)

It is pointed out that the internal structure of the narrow resonance X(3872) at the D^0 {\bar D}^{*0} threshold can be studied in some detail by measuring the rate and the spectra in the decays X(3872) \to D^0 {\bar D}^0 π^0 and X(3872) \to D^0 {\bar D}^0 γ. In particular, if this resonance contains a dominant `molecular' component D {\bar D^*} \pm {\bar D} D^*, this component can be revealed and studied by a distinct pattern of interference between the underlying decays of D^{*0} and {\bar D}^{*0} whose coherence is ensured by fixed (but yet unknown) C parity of the X(3872).

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arXiv2003

Remarks on the decays chi_{bJ}^\prime -> omega Upsilon

The recently observed by CLEO cascade decays Upsilon(3S) -> gamma chi_{bJ}^\prime -> gamma omega Upsilon are discussed. It is shown that within the nonrelativistic description of bottomonium in the heavy b quark limit, the ratio of the rates of the transitions chi_{bJ}^\prime -> omega Upsilon with J=1 and J=2 should be given by the ratio of the corresponding S wave phase space factors. As a result, the rate of the observed cascade transitions through the chi_{b2}^\prime resonance should be close to that through the chi_{b1}^\prime. It is suggested that the ratio of the discussed cascade rates can also be tested by measuring a simple angular correlation.

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arXiv2003

The enhancement of the decay Upsilon(1D) -> eta Upsilon(1S) by the axial anomaly in QCD

It is shown that the rates of the decays Upsilon(1^3D_1) -> eta Upsilon(1S) and Upsilon(1^3D_2) -> eta Upsilon(1S) should be comparable to and likely exceed that of the recently discussed in the literature two-pion transition Upsilon(1D) -> pi pi Upsilon(1S). The reason for this behavior is that the discussed eta transitions are enhanced by the contribution of the anomaly in the flavor singlet axial current in QCD.

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arXiv2003

Variation of the relative yield of charged and neutral B mesons across the Upsilon(4S) resonance

It is shown that the ratio of the production rates of the pairs (B+ B-) and (B0 anti-B0) should experience a substantial and rapid variation with energy within the width of the Upsilon(4S) resonance, crossing the value of one near the center of the resonance. This behavior is due to an interference of the rapidly changing with energy Breit-Wigner phase with the phase introduced in the wave function of charged mesons by their Coulomb interaction.

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arXiv2002

The onset of e^+e^- -> tau^+ tau^- at threshold revisited

The precise knowledge of the onset of the cross section $σ(e^+e^- \to τ^+τ^-)$ at the threshold is necessary for improving the accuracy of determination of the $τ$ mass from the threshold measurements. The QED radiative corrections of relative order $α$ and $α^2$, additional to the well known Coulomb factor, are considered in the threshold region. The correction terms of order $α^2$ are calculated, which contain coefficients enhanced by large parameters. As a result it is argued that the known $O(α)$ corrections provide the accuracy of the description of the cross section close to $10^{-4}$, rather than $10^{-3}$ as claimed in a recent literature. Also analytical expressions are provided for some limiting cases of the corrections, previously calculated numerically.

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arXiv2002

The Forward-Backward Asymmetry of B to (pi,K) l^+ l^-: Supersymmetry at Work

We analyze the forward-backward asymmetry of the decays B to (pi,K) l^+ l^- with l = mu or tau in the framework of the constrained minimal supersymmetric standard model. We find that, the asymmetry is enhanced at large tan beta and depends strongly on the sign of the mu parameter. For mu > 0, the asymmetry is typically large and observable whereas for mu < 0, it changes the sign and is suppressed by an order of magnitude. Including cosmological constraints we find that the asymmetry has a maximal value of about 30 %, produced when Higgs- and gauge- induced flavor violations are of comparable size, at a value of tan beta simeq 35. The present constraints from the B-factories are too weak to constrain parameter space, and the regions excluded by them are already disfavoured by at least one of B to X_s gamma, g-2, and/or cosmology. The size of the asymmetry is mainly determined by the flavor of the final state lepton rather than the flavor of the pseudoscalar.

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arXiv2002

The decay eta_c^prime -> eta_c pi pi

It is pointed out that the decay of the recently observed charmonium eta_c^prime resonance, eta_c^prime -> eta_c pi pi is simply related to the well studied decay psi^prime -> J/psi pi pi and can thus be used for absolute normalization of other decay modes of the eta_c^prime. The total rate of the discussed decay should be approximately three to four times the corresponding rate for the psi^prime$ resonance making the channel with charged pions the most probable exclusive decay mode of the eta_c^prime with the branching ratio in the range 5-10 %.

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arXiv2002

Non-factorizable terms, heavy quark masses, and semileptonic decays of D and B mesons

The non-factorizable terms in the operator product expansion have been recognized as one of theoretical obstacles for precision determination of the mixing parameter $V_{ub}$ from semileptonic B decays. It is pointed out here that the recent CLEO data on the parameters of the heavy quark expansion $λ_1$ and ${\bar Λ}$, combined with a theoretical bound on $λ_1$ strongly favor the existence of a sizeable contribution of non-factorizable terms in semileptonic decays of $D$ mesons. Thus these terms are likely to solve the long-standing problem of the deficit of semileptonic decay rate of the $D$ mesons, and with better data their magnitude can be determined and used in studies of the parameter $V_{ub}$.

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arXiv2001

More remarks on suppression of large black hole production in particle collisions

The problem of evaluating the cross section of production of large black holes in particle collisions at trans-Planckian energies is revisited. It is argued that the geometric cross section claimed in the literature would in fact lead to an exponentially growing with energy total cross section dominated by production of many "small" black holes. On the other hand, the semiclassical treatment of this problem, leading to an exponentially suppressed cross section for production of large black holes, requires that in the classical limit the cross section vanishes for massless colliding particles. The latter behavior can in principle be probed by numerical simulations in the classical general relativity.

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arXiv2001

Semiclassical suppression of black hole production in particle collisions

It is argued that the cross section for production of large black holes, for which a semiclassical description is applicable, cannot be given by the geometric area of the black hole horizon, as claimed recently in the literature. Rather the production cross section in a few-particle collision is suppressed by at least a factor exp(-I_E) with I_E being the Gibbons-Hawking (Euclidean) action for the black hole. Thus only essentially non-classical small black holes with mass of the order of the Planck mass can possibly be produced in few-particle collisions at trans-Planckian energies.

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arXiv2001

Non-factorization effects in heavy mesons and determination of |V_{ub}| from inclusive semileptonic B decays

The effects of spectator light quark in decays of heavy mesons are considered, which vanish in the limit of factorization of matrix elements of four-quark operators over the mesons. These effects include the difference of the total widths as well as of the semileptonic decay rates between the D^0 and D_s mesons and also a contribution to inclusive semileptonic decay rates of B^0 and B^\pm into the channel X_u l nu related to determination of the weak mixing parameter V_{ub}. If the observed difference of the lifetimes between D_s and D^0 mesons is attributed to non-factorizable terms, such terms can naturally give rise to a significant difference in inclusive semileptonic decay rates of these mesons, and to a light-flavor dependent contribution to decays B -> X_u l nu. The latter contribution affects mostly the upper part of the inclusive spectrum of the invariant mass of the lepton pair, and may significantly exceed the previously claimed in the literature theoretical uncertainty in determination of |V_{ub}|^2 from that part of the spectrum.

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arXiv2001

Once again on electromagnetic properties of a domain wall interacting with charged fermions

The response to a magnetic flux is considered of the vacuum state of charged Dirac fermions interacting with a domain wall made of a neutral spinless field in (3+1) dimensions with the fermion mass having a phase variation across the wall. It is pointed out that due to simple C parity arguments the spontaneous magnetization for this system is necessarily zero, thus invalidating some claims to the contrary in the literature. The cancellation of the spontaneous magnetization is explicitly demonstrated in a particular class of models. The same calculation produces a general formula for the electric charge density induced by the magnetic flux -- an effect previously discussed in the literature for axionic domain walls. The distribution of the induced charge is calculated in specific models.

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arXiv2000

The b-quark EDM in SUSY and CP-odd bottomonium formation

We compute the electric dipole moment (EDM) of the bottom quark in minimal supersymmetric model (SUSY) with explicit CP violation. We estimate its upper bound to be 10^(-20) e-cm where the dominant contribution comes from the charginos for most of the SUSY parameter space. We also find that chargino contribution is directly correlated with the branching fraction of the B\to X_s γdecay. Furthermore, we analyze the formation of 1 P_1 resonance of the (\bar{b}b) system in e^+ e^- annihilation, and show that the CP-violating transition amplitude, induced solely by the b-quark EDM, is significantly larger than the CP-conserving ones. Therefore, observation of this CP-odd resonance in e^+ e^- annihilation will be a direct probe of the CP-violating phases in SUSY. In case experiment cannot establish the existence of such a CP-odd (\bar{b}b) state, then either sparticle masses of all three generations will be pushed well above TeV, weakening the possibility of weak-scale SUSY, or the sparticle mass spectrum will be tuned so as to cancel different contributions to EDMs.

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arXiv2000

Decays of b hadrons and a possible new four-quark interaction

A possibility is considered of explaining the low experimental value of the ratio of the lifetimes tau(Lambda_b)/tau(B_d) by a new `centiweak' four-quark interaction, i.e with a strength on the order of 10^{-2}G_F. It is noted that the considered interaction can also improve agreement with the data on low semileptonic branching ratio B_{sl}(B) in B meson decays with a simultaneous slight decrease in the prediction for the average charm yield in those decays. The proposed new interaction modifies within the present experimental limits the predictions for differences of lifetimes among B mesons, and can thus be probed by more precise data on these differences. A sample model is briefly discussed, where the new interaction arises through a weak SU(2) singlet scalar field with quantum numbers of a diquark.

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arXiv2000

No Primordial Magnetic Field from Domain Walls

It is pointed out that, contrary to some claims in the literature, the domain walls cannot be a source of a correlated at large scales primordial magnetic field, even if the fermionic modes bound on the wall had ferromagnetic properties. In a particular model with massive (2+1) dimensional fermions bound to a domain wall, previously claimed to exhibit a ferromagnetic behavior, it is explicitly shown that the fermionic system in fact has properties of a normal diamagnetic with the susceptibility vanishing at high temperature.

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arXiv2000

Inclusive weak decay rates of heavy hadrons

A compact review of the theory, including some recent developments, of inclusive weak decay rates of charmed and b hadrons with an emphasis on predictions that can be tested in the forthcoming experiments.

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arXiv2000

Weak decays Xi_Q -> Lambda_Q pi

The weak decays Xi_b -> Lambda_b pi and Xi_c -> Lambda_c pi, in which the heavy quark is not destroyed, are discussed. The branching fractions for these decays, corresponding to an absolute rate of order 0.01 ps^{-1}, should be at a one percent level for the b hyperons and at a (few) per mill level for Xi_c, possibly making feasible their experimental study in future. It is shown, through an application of the heavy quark limit, the flavor SU(3) symmetry, and PCAC, that the Delta I = 1/2 rule should hold very well in these decays, and also that the Xi_b decays are purely S wave in the symmetry limit, while the difference between the $S$ wave amplitudes of the Xi_c decays and those for the Xi_b is related, in terms of the heavy quark expansion, to the difference of the total decay rates within the (Xi_c, Lambda_c) triplet of charmed hyperons. We also comment on the amplitudes of the semileptonic transitions Xi_Q -> Lambda_Q l nu and on the weak radiative decays Xi_Q -> Lambda_Q gamma.

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