17,211 research outputs found
Z_p scalar dark matter from multi-Higgs-doublet models
In many models, stability of dark matter particles is protected by a
conserved Z_2 quantum number. However dark matter can be stabilized by other
discrete symmetry groups, and examples of such models with custom-tailored
field content have been proposed. Here we show that electroweak symmetry
breaking models with N Higgs doublets can readily accommodate scalar dark
matter candidates stabilized by groups Z_p with any , leading to
a variety of kinds of microscopic dynamics in the dark sector. We give examples
in which semi-annihilation or multiple semi-annihilation processes are allowed
or forbidden, which can be especially interesting in the case of asymmetric
dark matter.Comment: 10 page
Entropy Bounds, Holographic Principle and Uncertainty Relation
A simple derivation of the bound on entropy is given and the holographic
principle is discussed. We estimate the number of quantum states inside space
region on the base of uncertainty relation. The result is compared with the
Bekenstein formula for entropy bound, which was initially derived from the
generalized second law of thermodynamics for black holes. The holographic
principle states that the entropy inside a region is bounded by the area of the
boundary of that region. This principle can be called the kinematical
holographic principle. We argue that it can be derived from the dynamical
holographic principle which states that the dynamics of a system in a region
should be described by a system which lives on the boundary of the region. This
last principle can be valid in general relativity because the ADM hamiltonian
reduces to the surface term.Comment: LaTeX, 8 pages, no figure
Scattering of twisted particles: extension to wave packets and orbital helicity
High-energy photons and other particles carrying non-zero orbital angular
momentum (OAM) emerge as a new tool in high-energy physics. Recently, it was
suggested to generate high-energy photons with non-zero OAM (twisted photons)
by the Compton backscattering of laser twisted photons on relativistic electron
beams. Twisted electrons in the intermediate energy range have also been
demostrated experimentally; twisted protons and other particles can in
principle be created in a similar way. Collisions of energetic twisted states
can offer a new look at particle properties and interactions. A theoretical
description of twisted particle scattering developed previously treated them as
pure Bessel states and ran into difficulty when describing the OAM of the final
twisted particle at non-zero scattering angles. Here we develop further this
formalism by incorporating two additional important features. First, we treat
the initial OAM state as a wave packet of a finite transverse size rather than
a pure Bessel state. This realistic assumption allows us to resolve the
existing controversy between two theoretical analyses for non-forward
scattering. Second, we describe the final twisted particle in terms of the
orbital helicity --- the OAM projection on its average direction of propagation
rather than on the fixed reaction axis. Using this formalism, we determine to
what extent the twisted state is transferred from the initial to final OAM
particle in a generic scattering kinematics. As a particular application, we
prove that in the Compton backscattering the orbital helicity of the final
photon stays close to the OAM projection of the initial photon.Comment: 18 pages, 4 figures; v2: expanded introduction and section 4.2 on
final orbital helicit
Wavelets and their use
This review paper is intended to give a useful guide for those who want to
apply discrete wavelets in their practice. The notion of wavelets and their use
in practical computing and various applications are briefly described, but
rigorous proofs of mathematical statements are omitted, and the reader is just
referred to corresponding literature. The multiresolution analysis and fast
wavelet transform became a standard procedure for dealing with discrete
wavelets. The proper choice of a wavelet and use of nonstandard matrix
multiplication are often crucial for achievement of a goal. Analysis of various
functions with the help of wavelets allows to reveal fractal structures,
singularities etc. Wavelet transform of operator expressions helps solve some
equations. In practical applications one deals often with the discretized
functions, and the problem of stability of wavelet transform and corresponding
numerical algorithms becomes important. After discussing all these topics we
turn to practical applications of the wavelet machinery. They are so numerous
that we have to limit ourselves by some examples only. The authors would be
grateful for any comments which improve this review paper and move us closer to
the goal proclaimed in the first phrase of the abstract.Comment: 63 pages with 22 ps-figures, to be published in Physics-Uspekh
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