arXiv subjects

M. B. Voloshin

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

134 records · Page 8Linked to original sources

arXiv1994

On normalization of QCD effects in $O(m_t^2)$ electroweak corrections

We point out that, contrary to some recent claims, there is no intrinsic long-distance uncertainty in perturbative calculation of the QCD effects in the $t \tb$ and $t \bb$ loops giving the electroweak corrections proportional to $m_t^2$. If these corrections are expressed in terms of the ``on-shell" mass $m_t$, the only ambiguity arising is that associated with the definition of the ``on-shell" mass of a quark. The latter is entirely eliminated if the result is expressed in terms of $m_t$ defined at short distances. Applying the Brodsky-Lepage-Mackenzie criterion for determining the natural scale for normalization of $\as$, we find that using the ``on-shell" mass makes this scale numerically small in units of $m_t$. Specifically, we find that by this criterion the first QCD correction to the $O(m_t^2)$ terms is determined by $\as^\msb(0.15 m_t)$. Naturally, a full calculation of three-loop graphs is needed to completely quantify the scale.

hep-ph↗

arXiv1993

E+ E- -> Tau+ Tau- at the Threshold and Beyond

The excitation curve for the $τ^+ \, τ^-$ production in electron positron annihilation near the threshold is revisited with the aim of updating and extending a previous work. We find that the corrections of the relative magnitude $O(α)$ near the threshold are significantly contributed by the radiative modification of the Coulomb interaction between the $τ$ leptons. The interpolation between the Coulomb effects at the threshold and the relativistic effects at higher energies is considered and the resulting formula is argued to have relative accuracy up to, but not including, terms of the order of $α^2$ at any velocity of the $τ$ leptons.

hep-ph↗

arXiv1993

Catalyzed decay of false vacuum in four dimensions

The probability of destruction of a metastable vacuum state by the field of a highly virtual particle with energy $E$ is calculated for a (3+1) dimensional theory in the leading WKB approximation in the thin-wall limit. It is found that the induced nucleation rate of bubbles, capable of expansion, is exponentially small at any energy. The negative exponential power in the rate reaches its maximum at the energy, corresponding to the top of the barrier in the bubble energy, where it is a finite fraction of the same power in the probability of the spontaneous decay of the false vacuum, i.e. at $E=0$.

hep-ph↗

arXiv1993

Non-Perturbative Production of Multi-Boson States and Quantum Bubbles

The amplitude of production of $n$ on-mass-shell scalar bosons by a highly virtual field $ϕ$ is considered in a $λϕ^4$ theory with weak coupling $λ$ and spontaneously broken symmetry. The amplitude of this process is known to have an $n!$ growth when the produced bosons are exactly at rest. Here it is shown that for $n \gg 1/λ$ the process goes through `quantum bubbles', i.e. quantized droplets of a different vacuum phase, which are non-perturbative resonant states of the field $ϕ$. The bubbles provide a form factor for the production amplitude, which rapidly decreases above the threshold. As a result the probability of the process may be heavily suppressed and may decrease with energy $E$ as $\exp (-const \cdot E^a)$, where the power $a$ depends on the number of space dimensions. Also discussed are the quantized states of bubbles and the amplitudes of their formation and decay.

hep-ph↗

arXiv1992

Some Properties of Amplitudes at Multi Boson Thresholds in Spontaneously Broken Scalar Theory

It is shown that in a $λϕ^4$ theory of one real scalar field with spontaneous breaking of symmetry a calculation of the amplitudes of production by a virtual field $ϕ$ of $n$ on-mass-shell bosons all being exactly at rest is equivalent in any order of the loop expansion to a Euclidean space calculation of the mean field of a kink-type configuration. Using this equivalence it is found that all the $1 \to n$ amplitudes have no absorptive part at the thresholds to any order of perturbation theory. This implies non-trivial relations between multi-boson threshold production amplitudes. In particular the on-mass-shell amplitude of the process $2 \to 3$ should vanish at the threshold in all loops. It is also shown that the factor $n!$ in the $1 \to n$ amplitudes at the threshold is not eliminated by loop effects.

hep-ph↗

arXiv1992

Zeros of Tree-Level Amplitudes at Multi-Boson Thresholds

Propagation of particles with emission of arbitrary number of identical bosons all being at rest is considered. It is shown that in certain models the tree-level amplitudes for production of $n$ scalar bosons by two incoming particles are all equal to zero at the threshold starting from some small number $n$. In particular this nullification occurs for production of massive scalars by two Goldstone bosons in the linear sigma model for $n > 1$ and also for production of Higgs bosons in the Standard Model by gauge bosons and/or by fermions, provided that the ratia of their masses to that of the Higgs boson take special discrete values.

hep-ph↗

arXiv1992

Comment on "Summing One-Loop Graphs at Multi-Particle Threshold"

The propagator of a virtual $ϕ$-field with emission of $n$ on-mass-shell particles all being exactly at rest is calculated at the tree-level in $λϕ^4$ theory by directly solving recursion equations for the sum of Feynman graphs. It is shown that the generating function for these propagators is equivalent to a Fourier transform of the recently found Green's function within the background-field technique for summing graphs at threshold suggested by Lowell Brown. Also the derivation of the result that the tree-level on-mass-shell scattering amplitudes of the processes $2 \to n$ are exactly vanishing at threshold for $n > 4$ is thus given in the more conventional Feynman diagram technique.

hep-ph↗

arXiv1992

Summing One-Loop Graphs at Multi-Particle Threshold

It is shown that the technique recently suggested by Lowell Brown for summing the tree graphs at threshold can be extended to calculate the loop effects. Explicit result is derived for the sum of one-loop graphs for the amplitude of threshold production of $n$ on-mass-shell particles by one virtual in the unbroken $λϕ^4$ theory. It is also found that the tree-level amplitude of production of $n$ particles by two incoming on-mass-shell particles vanishes at the threshold for $n > 4$.

hep-ph↗