arXiv subjects

M. B. Voloshin

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

At least 55 records · Page 3Linked to original sources

arXiv2013

Electric discharge in vacuum by minicharged particles

We discuss the possibility of a laboratory search for light minicharged particles carrying electric charge that is a small fraction $ε$ of that of electron. We point out that the production of pairs of such particles in an electric field would result in a measurable discharge in vacuum of electrically charged objects. A realistic experiment may be sensitive to such particles at least down to $ε\sim 10^{-8}$ if their mass is below $\sim 10^{-4}$eV.

hep-ph↗

arXiv2013

Remarks on double Higgs boson production by gluon fusion at threshold

The amplitude of double Higgs boson production by the gluon fusion, $gg \to hh$, is known to be small due to cancellation between the graphs with the boson trilinear coupling and those with the coupling to the top quark. For this reason a study of this process was suggested as a sensitive probe of the Higgs sector nonlinearity. We calculate in a closed analytical form this amplitude at the threshold of the two bosons, where the cancellation is the strongest, and discuss the origin of the small value of the amplitude. We also note that the cancellation in the double boson production is in fact a part of a more general phenomenon of suppression of similar threshold amplitudes for multiple boson production, which, although not directly relevant to the actual top quark and the Higgs boson, can be useful in other studies.

hep-ph↗

arXiv2013

Isospin violation in the yield of S-wave heavy meson pairs near threshold

We consider production of overall neutral pairs consisting of heavy $D^{(*)}$ or $B^{(*)}$ meson and antimeson in the processes, where the pair can be created in an $S$-wave, such as $e^+e^- \to π^0 \, D^* \bar D^{(*)}$ and $e^+e^- \to γ\, D^{(*)} \bar D^{(*)}$, and similar reactions with $B^{(*)}$ mesons. The ratio $R^{c/n}$ of the yield of pairs of charged mesons to that of neutral mesons near the threshold for the heavy pair is strongly affected by the isospin breaking due to the isotopic mass differences and due to the Coulomb interaction between the charged mesons. The actual behavior of the isospin breaking in $R^{c/n}$ is also sensitive to the strong interaction between the heavy mesons, so that experimental measurement of this ratio can be used as a probe of this strong interaction. We calculate $R^{c/n}$ at and very near the threshold in terms of the isotopic scattering lengths for the meson pairs. In particular we find that the yield of pairs of charged mesons does not go to zero at exactly the threshold, but rather starts with a finite step, whose height depends on the value of the scattering length in a particular channel.

hep-ph↗

arXiv2013

Suppression of the S-wave production of (3/2)^+ + (1/2)^- heavy meson pairs in e^+e^- annihilation

The heavy meson-antimeson pairs, where one is an excited $\bigl ({3 \over 2} \bigr) ^+ $ meson and the other is a ground state $\bigl ({1 \over 2} \bigr) ^-$ meson, namely the pairs ($D_1(2420) \bar D$ + c.c.), ($D_1(2420) \bar D^*$ + c.c.), ($D_2(2460) \bar D^*$ + c.c.) in the charm sector and ($B_1(5721) \bar B$ + c.c.), ($B_1(5721) \bar B^*$ + c.c.), ($B_2(5747) \bar B^*$ + c.c.) in the bottom sector, are allowed, by the quantum numbers, to be produced in the $S$ wave in $e^+e^-$ annihilation. We show, however, that such $S$-wave production is forbidden by the heavy quark spin symmetry. Thus the yield of the considered meson pairs in $e^+e^-$ annihilation should be significantly suppressed near the respective thresholds. In our view, this substantially weakens the arguments for considering the Y(4260) charmonium-like resonance as a $D_1 \bar D$ molecular state.

hep-ph↗

arXiv2013

Z_c(3900) - what is inside?

The models for the internal structure of the newly found four-quark charmonium-like resonance $Z_c(3900)$ are discussed: the molecular model as well as the hadro-charmonium and tetraquark schemes. It is argued that it would be possible to resolve between these models by combining measurements of the quantum numbers of the resonance and of its decay rates into yet unseen channels $πψ'$, $πh_c$, $ρη_c$ and into pairs of heavy mesons $D^* \bar D$ and $D \bar D^*$. The models also predict different related four-quark states, which can be sought for in the existing and future data.

hep-ph↗

arXiv2013

Mixing of partial waves near $B^* \bar B^*$ threshold in $e^+e^-$ annihilation

We consider the production of $B^* \bar B^*$ meson pairs in $e^+e^-$ annihilation near the threshold. The rescattering due to pion exchange between the mesons results in a mixing between three partial wave amplitudes: two $P$-wave with the total spin of the meson pair S=0 and S=2 and an F-wave amplitude. The mixing due to pion exchange with a low momentum transfer is calculable up to c.m. energy $E \approx 15 ÷20$\,MeV above the threshold. We find that the $P-F$ mixing is numerically quite small in this energy range, while the mixing of the two P-wave amplitudes is rapidly changing with energy and can reach of order one at such low energies.

hep-ph↗

arXiv2013

Enhanced mixing of partial waves near threshold for heavy meson pairs and properties of $Z_b(10610)$ and $Z_b(10650)$ resonances

The mixing of $S-D$ partial waves for the heavy meson pairs in the decays $Υ(5S) \to [B^* \bar B+ {\rm c.c.}] π$ and $Υ(5S) \to B^* \bar B^* π$ is considered. It is argued that this mixing, enhanced by the heavy meson mass, is calculable as dominated by a rescattering through pion exchange if the production of the heavy mesons is dominated by $S$-wave `molecular' resonances $Z_b(10610)$ and $Z_b(10650)$. The effect of the mixing grows with the c.m. energy $E$ in each channel over the threshold, and may reach $10 ÷20$% in the rate at the upper end of applicability of the discussed approach, $E \sim 15 $MeV. It is also argued that the mixing is likely to reach maximum at energy approximately equal to the mass gap between the thresholds.

hep-ph↗

arXiv2012

Pion transitions from χ_{cJ} to η_c

The charmonium transitions from the $χ_{cJ}$ states to $η_c$ with emission of one or two pions are considered. It is shown that the only processes of such type arising in the leading order in the QCD multipole expansion are the decays $χ_{c1} \to η_c π^+ π^-$ and $χ_{c0} \to η_c π^0$. The absolute rate of the latter decay, in spite of being isotopically suppressed, is by about an order of magnitude larger than that of the former, so that the branching fractions for the two processes are approximately equal, and are expected to be significantly below the recent upper bound reported by BESIII. The rates of both decays are also related to that of another similar transition $h_c \to J/ψπ^0$.

hep-ph↗

arXiv2012

CP Violation in Higgs Diphoton Decay in Models with Vectorlike Heavy Fermions

The amplitude of the diphoton decay of the Higgs boson is considered in an extension of the Standard Model involving heavy vectorlike fermions, which was recently suggested in the literature in order to explain a possible enhancement of the h -> gamma gamma decay rate. It is pointed out that generally in such models the decay amplitude acquires a sizable CP-odd contribution from the complex phases in the mass matrix of the new heavy fermions. The resulting CP violation in the diphoton decay can be studied experimentally when both photons are converted into e^+ e^- pairs by measuring the distribution over the angle between the planes of the pairs. Such measurement, if feasible, would be of a great interest on its own, regardless specific models.

hep-ph↗

arXiv2012

Remarks on decays of h_b(2P)

We consider hadronic transitions from the $h_b(2P)$ bottomonium resonance to lower states of bottomonium with emission of either $ω$ meson, or two pions, or $η$ meson. For the former two transitions the branching ratios are related to similar transitions from $χ_{b1}(2P)$ and the recently measured by Belle fractions of the radiative decays of $h_b(2P)$. We argue that the fraction of the $h_b(2P)$ total decay rate remaining for the annihilation rate is on the verge of contradiction with the `parton' picture of bottomonium annihilation resulting in similarity between the decays of $h_b(1,2P)$ and $χ_{b1}(1,2P)$. The contradiction gets even stronger, if the transition $h_b(2P) \to Υ(1S) \, η$ has branching fraction of a few percent or more. We argue that, although quite uncertain, the latter fraction may indeed be that significant.

hep-ph↗

arXiv2012

Z_b(10610) and Z_b(10650) decays to bottomonium plus pion

We consider the transitions from the $Z_b(10610)$ and $Z_b(10650)$ resonances to the states of bottomonium with emission of a pion. The $Z_b$ resonances are viewed as `molecular' objects of a large spatial size made of heavy $B^{(*)}$ mesons, while the states of bottomonium are considered to be compact, so that an application of the leading (dipole) term in the QCD multipole expansion is assumed to be justified. In this way we calculate the ratios of the decay rates to the final states $Υ(nS)\, π$ with $n=1,2,3$, and the ratio of the decay rates to $h_b(kP)\, π$ with $k=1$ and 2. We find our estimates in a reasonable agreement with recent experimental data.

hep-ph↗

arXiv2012

Charged-to-neutral heavy meson yield ratio at the Z_b^0 resonances as a probe of the I^G(J^P)=0^-(1^+) channel

It is argued that the ratio of the yield of pairs of charged and neutral $B^{(*)}$ mesons in the processes $Υ(5S) \to π^0 + (B \bar B^* + c.c.)$ and $Υ(5S) \to π^0 + B^* \bar B^*$ is very sensitive near the corresponding heavy meson threshold to the strong interaction between the mesons in the $I^G(J^P)=0^-(1^+)$ channel due to significant isospin breaking by the Coulomb force. This channel, not readily accessible by other means, may contain near-threshold molecular meson-antimeson resonances --- isoscalar analogs of the isovector states $Z_b(10610)$ and $Z_b(10650)$.

hep-ph↗

arXiv2012

Heavy quark spin symmetry breaking in near-threshold $J^{PC}=1^{--}$ quarkonium-like resonances

A mixing of near-threshold quarkonium-like resonances with heavy meson-antimeson pairs results in an enhancement of heavy quark spin symmetry breaking, since the meson pairs are not eigenstates of the heavy quark spin. The decomposition of $P$-wave states of meson pairs in terms of the heavy-quark-pair spin states is considered in the channel with $J^{PC}=1^{--}$, which is directly produced in $e^+e^-$ annihilation. Specific processes are suggested for experimental study of the effects of the mixing with heavy meson pairs and of the internal spin structure of bottomonium and charmonium resonances.

hep-ph↗

arXiv2011

A gamma-ray signature of energetic sources of cosmic-ray nuclei

Astrophysical sources of nuclei are expected to produce a broad spectrum of isotopes, many of which are unstable. An unstable nucleus can beta-decay outside the source into a single-electron ion. Heavy one-electron ions, thus formed, can be excited in their interactions with cosmic microwave background photons, in which case they relax to the ground state with the emission of a gamma ray. Repetitive cycles of excitation and gamma-ray emission can produce an observable feature in the gamma-ray spectrum with a maximum around 8 GeV (for iron). We find that the observed spectrum of Centaurus A is consistent with a substantial flux of nuclei accelerated to 0.1 EeV. A characteristic 5--10 GeV (iron) shoulder in the gamma-ray spectra of various sources can help identify astrophysical accelerators of nuclei or set upper limits on nuclear acceleration.

astro-ph.HE↗

arXiv2011

Higgs Decay into Two Photons through the W-boson Loop: No Decoupling in the m_W --> 0 Limit

We reanalyze the W-boson loop in the amplitude of the Higgs decay into two photons to show the absence of decoupling in the limit of massless W bosons, m_W --> 0. The Higgs coupling to longitudinal polarizations survive in this limit and generates a nonvanishing contribution in the $H\to γγ$ decay. This shows that the recent claim of decoupling by R. Gastmans, S.L. Wu, and T.T. Wu is incorrect, and the old calculations for the two photon decay well known in the literature are valid.

hep-ph↗

arXiv2011

Radiative transitions from Upsilon(5S) to molecular bottomonium

The heavy quark spin symmetry implies that in addition to the recently observed Z(10610) and Z(10650) molecular resonances with $I^G=1^+$ there should exist two or four molecular bottomonium-like states with $I^G=1^-$. Properties of these G-odd states are considered, including their production in the radiative transitions from Upsilon(5S), by applying the same symmetry to the Upsilon(5S) resonance and the transition amplitudes. The considered radiative processes can provide a realistic option for observing the yet hypothetical states.

hep-ph↗

arXiv2011

Testing neutrino magnetic moment in ionization of atoms by neutrino impact

The atomic ionization processes induced by scattering of neutrinos play key roles in the experimental searches for a neutrino magnetic moment. Current experiments with reactor (anti)neutrinos employ germanium detectors having energy threshold comparable to typical binding energies of atomic electrons, which fact must be taken into account in the interpretation of the data. Our theoretical analysis shows that the so-called stepping approximation to the neutrino-impact ionization is well applicable for the lowest bound Coulomb states, and it becomes exact in the semiclassical limit. Numerical evidence is presented using the Thomas-Fermi model for the germanium atom.

hep-ph↗

arXiv2011

Heavy quark spin structure in Z_b resonances

We discuss the heavy quark spin structure of the recently observed `twin' resonances $Z_b(10610)$ and $Z_b(10650)$ assuming that these are mostly of a `molecular' type, i.e. that their internal dynamics is dominated by the coupling to meson pairs $B^* \bar B - B {\bar B}^*$ and $B^* {\bar B}^*$. We find that the state of the $b \bar b$ pair within the $Z_b(10610)$ and $Z_b(10650)$ resonances is a mixture of a spin-triplet and a spin-singlet of equal amplitude and with the phase orthogonal between the two resonances. Such a structure gives rise to specific relations between observable amplitudes that are in agreement with the data obtained recently by Belle. We also briefly discuss possible properties of the isotopically singlet counterparts of the newly found resonances, and also of their $C$ ($G$) parity opposites that likely exist in the same mass range near the open $B$ flavor threshold.

hep-ph↗