M. B. Voloshin

Secluded WIMP dark matter

We consider a generic mechanism via which thermal relic WIMP dark matter may be decoupled from the Standard Model, namely through a combination of WIMP annihilation to metastable mediators with subsequent delayed decay to Standard Model states. We illustrate this with explicit examples of WIMPs connected to the Standard Model by metastable bosons or fermions. In all models, provided the WIMP mass is greater than that of the mediator, it can be secluded from the Standard Model with an extremely small elastic scattering cross-section on nuclei and rate for direct collider production. In contrast, indirect signatures from WIMP annihilation are consistent with a weak scale cross-section and provide potentially observable γ-ray signals. We also point out that γ-ray constraints and flavor physics impose severe restrictions on MeV-scale variants of secluded models, and identify limited classes that pass all the observational constraints.

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

Abstract It is pointed out that the internal structure of the narrow resonance X(3872) at the D 0 D ∗0 threshold can be studied in some detail by measuring the rate and the spectra in the decays X(3872)→D 0 D 0 π 0 and X(3872)→D 0 D 0 γ . In particular, if this resonance contains a dominant “molecular” component D D ∗ ± D D ∗ , this component can be revealed and studied by a distinct pattern of interference between the underlying decays of D ∗0 and D ∗0 whose coherence is ensured by fixed (but yet unknown) C parity of the X(3872).

Bosonic super-WIMPs as keV-scale dark matter

We consider models of light superweakly interacting cold dark matter, with O(10-100) keV mass, focusing on bosonic candidates such as pseudoscalars and vectors. We analyze the cosmological abundance, the {gamma} background created by particle decays, the impact on stellar processes due to cooling, and the direct-detection capabilities in order to identify classes of models that pass all the constraints. In certain models, variants of photoelectric (or axioelectric) absorption of dark matter in direct-detection experiments can provide a sensitivity to the superweak couplings to the standard model which is superior to all existing indirect constraints. In all models studied, the annual modulation of the direct-detection signal is at the currently unobservable level of O(10{sup -5})

Semiclassical suppression of black hole production in particle collisions

Abstract 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.

Anomaly and quantum corrections to solitons in two-dimensional theories with minimal supersymmetry

We reexamine the issue of the soliton mass in two-dimensional models with N=1 supersymmetry. The superalgebra has a central extension, and at the classical level the soliton solution preserves 1/2 of supersymmetry which is equivalent to BPS saturation. We prove that the property of BPS saturation, i.e. the equality of the soliton mass to the central charge, remains intact at the quantum level in all orders of the weak coupling expansion. Our key finding is an anomaly in the expression for the central charge. The classical central charge, equal to the jump of the superpotential, is amended by an anomalous term proportional to the second derivative of the superpotential. The anomaly is established by various methods in explicit one-loop calculations. We argue that this one-loop result is not affected by higher orders. We discuss in detail how the impact of the boundary conditions can be untangled from the soliton mass calculation. In particular, the soliton profile and the energy distribution are found at one loop. A {open_quotes}supersymmetry{close_quotes} in the soliton mass calculations in the non-supersymmetric models is observed. {copyright} {ital 1999} {ital The American Physical Society}

ηc puzzle in quantum chromodynamics

The mass of the η c meson is calculated by means of QCD sum rules. If the spectrum of the 0 − states of charmonium contains a single prominent resonance, like the J/ψ in the case of vector states, then the η c mass is 3.0 GeV, not 2.83. There is a possibility however that there are two mixed 0 − states with close masses. Then the X(2.83) could be one of them. The other one however has a much larger coupling to the pseudoscalar current of c quarks and is a “true” η c . The η c mass in the case of two mixed states is 3.0-3.2 GeV.

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

Abstract 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.

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 {open_quotes}integrals of motion{close_quotes} exist. The solution for the profile of the scalar fields for any wall belonging to the family is found in quadratures for an 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. Unexpected nullifications of the threshold amplitudes are found. {copyright} {ital 1998} {ital The American Physical Society}

Large O(mc−2) nonperturbative corrections to the inclusive rate of the decay B → Xsγ☆

It is shown that the inclusive rate of the rare weak radiative decays B → Xsγ contains a series of nonperturbative corrections, whose ‘short distance’ scale is set by mc−1, rather than by mb−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 〈B|bσ · Gb|B〉mc2. Though the magnitude of this first correction is s by a numerical coefficient, the sensitivity of the decay rate to the distance scale mc−1 may significantly limit the accuracy of purely perturbative predictions for the rate.

Marginal stability and the metamorphosis of Bogomol’nyi-Prasad-Sommerfield states

We discuss the restructuring of the BPS spectrum which occurs on certain submanifolds of the moduli/parameter space – the curves of the marginal stability (CMS) – using quasiclassical methods. We argue that in general a ‘composite’ BPS soliton swells in coordinate space as one approaches the CMS and that, as a bound state of two ‘primary’ solitons, its dynamics in this region is determined by supersymmetric quantum mechanics with a short range potential. Near the CMS the bound state resembles a deuteron with a wave function which is highly spread out. Precisely on the CMS the bound state level reaches the continuum, the composite state delocalizes in coordinate space, and restructuring of the spectrum can occur. We present a detailed analysis of this behavior in a two-dimensional N= 2 Wess-Zumino model with two chiral fields, and then discuss how it arises in the context of ‘composite’ dyons near weak coupling CMS curves in N = 2 supersymmetric gauge theories. We also consider exceptional cases where some states become massless on the CMS.