421 research outputs found
Instanton - like transitions at high energies in (1+1) dimensional scalar models. II.Classically allowed induced vacuum decay
We consider classical Minkowskian solutions to the field equation in the
(1+1) dimensional scalar model with the exponential interaction that describe
the unsuppressed false vacuum decay induced by initial particles. We find
that there is a critical value of below which there are no such solutions,
i.e., the vacuum decay is always suppressed. For the number of initial
particles larger than this value the vacuum decay is unsuppressed at high
enough energies.Comment: 18 pages, 2 figures, LaTex, figures in PS, INR-T-94/
Semiclassical Study of Baryon and Lepton Number Violation in High-Energy Electroweak Collisions
We make use of a semiclassical method for calculating the suppression
exponent for topology changing transitions in high-energy electroweak
collisions. In the Standard Model these processes are accompanied by violation
of baryon and lepton number. By using a suitable computational technique we
obtain results for s-wave scattering in a large region of initial data. Our
results show that baryon and lepton number violation remains exponentially
suppressed up to very high energies of at least 30 sphaleron masses (250 TeV).
We also conclude that the known analytic approaches inferred from low energy
expansion provide reasonably good approximations up to the sphaleron energy (8
TeV) only.Comment: 23 pages, 18 figures. Phys.Rev.D journal version (two references
added
Cosmology with non-minimal scalar field: graceful entrance into inflation
We propose a scenario of the beginning of inflation in which the non-vacuum
value of the scalar field that drives inflation develops dynamically due to the
non-minimal coupling to gravity. In this scenario, inflation emerges as an
intermediate stage of the evolution of the Universe, well after the Planck
epoch, from a fairly general initial state.Comment: LaTeX, uses axodraw style, 7 pages, 1 ps-figur
The cosmological constant and dark energy in braneworlds
We review recent attempts to address the cosmological constant problem and
the late-time acceleration of the Universe based on braneworld models. In
braneworld models, the way in which the vacuum energy gravitates in the 4D
spacetime is radically different from conventional 4D physics. It is possible
that the vacuum energy on a brane does not curve the 4D spacetime and only
affects the geometry of the extra-dimensions, offering a solution to the
cosmological constant problem. We review the idea of supersymmetric large extra
dimensions that could achieve this and also provide a natural candidate for a
quintessence field. We also review the attempts to explain the late-time
accelerated expansion of the universe from the large-distance modification of
gravity based on the braneworld. We use the Dvali-Gabadadze-Porrati model to
demonstrate how one can distinguish this model from dark energy models in 4D
general relativity. Theoretical difficulties in this approach are also
addressed.Comment: Invited Review for a special Gen. Rel. Grav. issue on Dark Energy, 22
pages, 13 figures, references adde
More about spontaneous Lorentz-violation and infrared modification of gravity
We consider a model with Lorentz-violating vector field condensates, in which
dispersion laws of all perturbations, including tensor modes, undergo
non-trivial modification in the infrared. The model is free of ghosts and
tachyons at high 3-momenta. At low 3-momenta there are ghosts, and at even
lower 3-momenta there exist tachyons. Still, with appropriate choice of
parameters, the model is phenomenologically acceptable. Beyond a certain large
distance scale and even larger time scale, the gravity of a static source
changes from that of General Relativity to that of van Dam--Veltman--Zakharov
limit of the Fierz--Pauli theory. Yet the late time cosmological evolution is
always determined by the standard Friedmann equation, modulo small correction
to the ``cosmological Planck mass'', so the modification of gravity cannot by
itself explain the accelerated expansion of the Universe. We argue that the
latter property is generic in a wide class of models with condensates.Comment: 15 pages, 1 figure, JHEP3.cls; Added reference
Towards the realistic fermion masses with a single family in extra dimensions
In a class of multidimensional models, topology of a thick brane provides
three chiral fermionic families with hierarchical masses and mixings in the
effective four-dimensional theory, while the full model contains a single
vector-like generation. We carry out numerical simulations and reproduce all
known Standard Model fermion masses and mixings in one of these models.Comment: 12 pages, 2 figures, uses JHEP3.cls. Some minor corrections are mad
An Example of Semiclassical Instanton-Like Scattering: (1+1) Dimensional Sigma Model
A solution to the classical field equations in the massless (1+1)-dimensional
O(3) sigma model is found, which describes a multi-particle instanton-like
transition at high energy. In the limit of small number of initial particles,
the number of final particles is shown to be also small, and the probability of
the transition is suppressed by , where is the instanton
action. This solution, however, does not correspond to the maximum transition
probability among all states with given number of incoming particles and
energy. Unless the limit is exponentially sensitive to
the structure of the initial state, our results imply that well above the
sphaleron energy, the instanton-induced cross section becomes again suppressed
by the instanton exponent, and the number of final paricles is again small.Comment: 28 pages, LaTeX preprint TPI-MINN-92/66-
Chern-Simons number asymmetry from CP violation at electroweak tachyonic preheating
We consider the creation of non-zero Chern-Simons number in a model of the
early Universe, where the Higgs field experiences a fast quench at the end of
inflation and subsequently rolls down its potential barrier. Neglecting the
expansion, we perform numerical lattice simulations in the Abelian Higgs model
in 1+1 dimensions with an added phenomenological C and P violating term during
this stage of so-called tachyonic preheating. The results suggest that even the
sign of the Chern-Simons and thus baryon number is dependent on the ratio of
the Higgs to W mass. We also discuss the appropriate choice of vacuum initial
conditions for classical simulations.Comment: 24 pages, 17 figures, added references, published versio
Doubling of background solution in 5D stabilized brane world model
We discuss a model providing two different stationary background solutions
with flat and metric on the branes under the same values of the
fundamental parameters. It is shown that only an additional fine-tuning of the
brane scalar field potentials can provide a separation between two background
solutions.Comment: 7 pages, LaTeX, typos correcte
Vector field localization and negative tension branes
It is shown that negative tension branes in higher dimensions may lead to an
effective lower dimensional theory where the gauge-invariant vector fields
associated with the fluctuations of the metric are always massless and
localized on the brane. Explicit five-dimensional examples of this phenomenon
are provided. Furthermore, it is shown that higher dimensional gauge fields can
also be localized on these configurations with the zero mode separated from the
massive tower by a gap.Comment: 16 pages, LaTeX style; to appear in Phys. Rev.
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