arXiv subjects
Publications and source records attributed to Mikhail Shaposhnikov.
We show that the extension of the standard model by three right-handed neutrinos with masses smaller than the electroweak scale (the $ν$MSM) can explain simultaneously dark matter and baryon asymmetry of the universe and be consistent with the experiments on neutrino oscillations. Several constraints on the parameters of the $ν$MSM are derived.
We investigate an extension of the Minimal Standard Model by right-handed neutrinos (the $ν$MSM) to incorporate neutrino masses consistent with oscillation experiments. Within this theory, the only candidates for dark matter particles are sterile right-handed neutrinos with masses of a few keV. Requiring that these neutrinos explain entirely the (warm) dark matter, we find that their number is at least three. We show that, in the minimal choice of three sterile neutrinos, the mass of the lightest active neutrino is smaller than ${\cal O}(10^{-5})$ eV, which excludes the degenerate mass spectra of three active neutrinos and fixes the absolute mass scale of the other two active neutrinos.
If inflaton couples very weakly to ordinary matter the reheating temperature of the universe can be lower than the electroweak scale. In this letter we show that the late reheating occurs in a highly non-uniform way, within narrow areas along the jets produced by ordinary particles originated from inflaton decays. Depending on inflaton mass and decay constant, the initial temperature inside the lumps of the overheated plasma may be large enough to trigger the unsuppressed sphaleron processes with baryon number non-conservation, allowing for efficient local electroweak baryogenesis.
Starting from an anomaly-free Abelian Higgs model coupled to gravity in a 6-dimensional space-time we construct an effective four-dimensional theory of charged fermions interacting with U(1) Abelian gauge field and gravity, both localised near the core of a Nielsen-Olesen vortex configuration. We show that an anomaly free theory in 6-dimensions can give rise to an anomalous theory in D=4, which suggests a possibility of consistent regularisation of abelian anomalous chiral gauge theories in four dimensions. We also show that the spectrum of charged bulk fermions has a mass gap.
In this paper we develop a formalism to analyze the spectrum of small perturbations about arbitrary solutions of Einstein, Yang-Mills and scalar systems. We consider a general system of gravitational, gauge and scalar fields in a $D-$dimensional space-time and give the bilinear action for the fluctuations of the fields in the system around an arbitrary solution of the classical field equations. We then consider warped geometries, popular in brane world scenarios, and use the light cone gauge to separate the bilinear action into a totally decoupled spin-two, -one and -zero fluctuations. We apply our general scheme to several examples and discuss in particular localization of abelian and non-abelian gauge fields of the standard model to branes generated by scalar fields. We show in particular that the Nielsen-Olsen string solution gives rise to a normalizable localized spin-1 field in any number of dimensions.
We present regular solutions for a brane world scenario in the form of a 't Hooft-Polyakov monopole living in the three-dimensional spherical symmetric transverse space of a seven-dimensional spacetime. In contrast to the cases of a domain-wall in five dimensions and a string in six dimensions, there exist gravity-localizing solutions for both signs of the bulk cosmological constant. A detailed discussion of the parameter space that leads to localization of gravity is given. A point-like monopole limit is discussed.
We show that a pure gauge theory in higher dimensions may lead to an effective lower-dimensional theory with massive vector field, broken gauge symmetry and no fundamental Higgs boson. The mechanism we propose employs the localization of a vector field on a lower-dimensional defect. No non-zero expectation values of the vector field components along extra dimensions are required. New possibilities for the solution to the gauge hierarchy problem are discussed.
We study localization of bulk fermions on a brane with inclusion of Yang-Mills and scalar backgrounds in higher dimensions and give the conditions under which localized chiral fermions can be obtained.
In this note we argue that the breaking of conformal invariance because of the coupling of a charged scalar field to gravity is not sufficient for the production of seed galactic magnetic fields during inflation.
We consider spherically symmetric higher-dimensional solutions of Einstein's equations with a bulk cosmological constant and n transverse dimensions. In contrast to the case of one or two extra dimensions we find no solutions that localize gravity when $n\geq 3$, for strictly local topological defects. We discuss global topological defects that lead to the localization of gravity and estimate the corrections to Newton's law. We show that the introduction of a bulk ``hedgehog'' magnetic field leads to a regular geometry and localizes gravity on the 3-brane with either a positive, zero or negative bulk cosmological constant. The corrections to Newton's law on the 3-brane are parametrically the same as for the case of one transverse dimension.
We present a metric solution in six dimensions where gravity is localized on a four-dimensional singular string-like defect. The corrections to four-dimensional gravity from the bulk continuum modes are suppressed by ${\cal O}(1/r^3)$. No tuning of the bulk cosmological constant to the brane tension is required in order to cancel the four-dimensional cosmological constant.
We present new solutions of higher dimensional Einstein's equations with a cosmological constant that localize gravity on branes which are transverse to Ricci-flat manifolds or to homogeneous spaces with topologically non-trivial solutions of gauge field equations. These solutions are relevant for the localization of chiral fermions on a brane.
We present a novel scenario for baryogenesis in a hybrid inflation model at the electroweak scale, in which the Standard Model Higgs field triggers the end of inflation. One of the conditions for successful baryogenesis, the departure from thermal equilibrium, is naturally achieved at the stage of preheating after inflation. The inflaton oscillations induce large occupation numbers for long-wavelength configurations of Higgs and gauge fields, which leads to a large rate of sphaleron transitions. We estimate this rate during the first stages of reheating and evaluate the amount of baryons produced due to a particular type of higher dimensional CP violating operator. The universe thermalizes through fermion interactions, at a temperature below critical, $T_{rh} < 100$ GeV, preventing the wash-out of the produced baryon asymmetry. Numerical simulations in (1+1) dimensions support our theoretical analysis.
Theories with low-energy supersymmetry predict the existence of stable non-topological solitons, Q-balls, that can contribute to dark matter. We discuss the experimental signatures, methods of detection, and the present limits on such dark matter candidates.
Electroweak models with low-energy supersymmetry breaking predict the existence of stable non-topological solitons, Q-balls, that can be produced in the early universe. The relic Q-balls can accumulate inside a neutron star and gradually absorb the baryons into the scalar condensate. This causes a slow reduction in the mass of the star. When the mass reaches a critical value, the neutron star becomes unstable and explodes. The cataclysmic destruction of the distant neutron stars may be the origin of the gamma-ray bursts.
We formulate a set of simple sufficient conditions for the existence of Q-balls in gauge theories.
Supersymmetric extensions of the standard model generically contain stable non-topological solitons, Q-balls, which carry baryon or lepton number. We show that large Q-balls can be copiously produced in the early universe, can survive until the present time, and can contribute to dark matter.
Future experiments may discover new scalar particles with global charges and couplings that allow for solitonic states. If the effective potential has flat directions, the scalar VEV inside a large Q-ball can exceed the particle mass by many orders of magnitude. Models with low-energy supersymmetry breaking generically have both the scalars carrying some global charges, and the flat directions. The Q-ball interior can, therefore, provide an environment for exploring physics far beyond the TeV scale without the need for building colliders of ever-increasing energies. Some Standard Model processes, otherwise strongly suppressed, can also be studied inside the soliton, where the SU(2) symmetry can be restored, and the quark confinement may be absent. Baryon number violating processes catalyzed by the large VEV inside the Q-ball can provide an inexhaustible energy resource.