98 research outputs found
True Neutrality as a New Type of Flavour
A classification of leptonic currents with respect to C-operation requires
the separation of elementary particles into the two classes of vector C-even
and axial-vector C-odd character. Their nature has been created so that to each
type of lepton corresponds a kind of neutrino. Such pairs are united in
families of a different C-parity. Unlike the neutrino of a vector type, any
C-noninvariant Dirac neutrino must have his Majorana neutrino. They constitute
the purely neutrino families. We discuss the nature of a corresponding
mechanism responsible for the availability in all types of axial-vector
particles of a kind of flavour which distinguishes each of them from others by
a true charge characterized by a quantum number conserved at the interactions
between the C-odd fermion and the field of emission of the corresponding types
of gauge bosons. This regularity expresses the unidenticality of truly neutral
neutrino and antineutrino, confirming that an internal symmetry of a
C-noninvariant particle is described by an axial-vector space. Thereby, a true
flavour together with the earlier known lepton flavour predicts the existence
of leptonic strings and their birth in single and double beta decays as a unity
of flavour and gauge symmetry laws. Such a unified principle explains the
availability of a flavour symmetrical mode of neutrino oscillations.Comment: 19 pages, LaTex, Published version in IJT
Does Bose-Einstein condensation of CMB photons cancel {\mu} distortions created by dissipation of sound waves in the early Universe?
The difference in the adiabatic indices of photons and non-relativistic
baryonic matter in the early Universe causes the electron temperature to be
slightly lower than the radiation temperature. Thermalization of photons with a
colder plasma results in the accumulation of photons in the Rayleigh-Jeans
tail, aided by stimulated recoil, while the higher frequency spectrum tries to
approach Planck spectrum at the electron temperature
T_{\gamma}^{final}=\Te; i.e., Bose-Einstein condensation
of photons occurs. We find new solutions of the Kompaneets equation describing
this effect. No actual condensate is, in reality, possible since the process is
very slow and photons drifting to low frequencies are efficiently absorbed by
bremsstrahlung and double Compton processes. The spectral distortions created
by Bose-Einstein condensation of photons are within an order of magnitude (for
the present range of allowed cosmological parameters), with exactly the same
spectrum but opposite in sign, of those created by diffusion damping of the
acoustic waves on small scales corresponding to comoving wavenumbers . The initial perturbations on these scales are completely
unobservable today due to their being erased completely by Silk damping. There
is partial cancellation of these two distortions, leading to suppression of
distortions expected in the standard model of cosmology. The net
distortion depends on the scalar power index and its running , and may vanish for special values of parameters, for example, for a running
spectrum with, . We arrive at an intriguing
conclusion: even a null result, non-detection of -type distortion at a
sensitivity of , gives a quantitative measure of the primordial
small-scale power spectrum.Comment: Published versio
About one long-range contribution to K+ -> pi+ l+ l- decays
We investigate the mechanism of K+ -> pi+ l+ l- (l= e, mu) decays in which a
virtual photon is emitted either from the incoming K+ or the outgoing pi+. We
point out some inconsistencies with and between two previous calculations,
discuss the possible experimental inputs, and estimate the branching fractions.
This mechanism alone fails to explain the existing experimental data by more
than one order-of-magnitude. But it may show itself by its interference with
the leading long-range mechanism dominated by the a_1^+ and rho^0 mesons.Comment: 12 pages, RevTeX, epsf.sty, 2 embedded figure
Effect of small scale density perturbations on the formation of dark matter halo profiles
With help of a set of toy N-body models of dark halo formation we study the
impact of small scale initial perturbations on the inner density profiles of
haloes. We find a significant flattening of the inner slope to in some range of scales and amplitudes
of the perturbations (while in the case of absence of these perturbations the
NFW profile with is reproduced). This effect may be responsible for
the formation of cuspless galactic haloes.Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letter
On the coupling between different species during recombination
Measurements of fluctuations in the Cosmic Microwave Background Radiation
(CMBR) is one of the most promising methods for measuring the fundamental
cosmological parameters. However, in order to infer parameters from precision
measurements it is necessary to calculate the theoretical fluctuation spectrum
to at least the measurement accuracy. Standard treatments assume that
electrons, ions and neutral hydrogen are very tightly coupled during the entire
recombination history, and that the baryon-photon plasma can be treated as a
two-fluid system consisting of baryons and photons interacting via Thomson
scattering. We investigate the validity of this approximation by explicitly
writing down and solving the full set of Boltzmann equations for electrons,
ions, neutral hydrogen and photons. The main correction to the standard
treatment is from including Rayleigh scattering between photons and neutral
hydrogen, a change of less than 0.1% in the CMBR power spectrum. Our conclusion
is thus that the standard treatment of the baryon-photon system is a very good
approximation, better than any possible measurement accuracy.Comment: 17 pages, 4 figs, version to appear in New Astronom
Fluctuations in the Cosmic Microwave Background I: Form Factors and their Calculation in Synchronous Gauge
It is shown that the fluctuation in the temperature of the cosmic microwave
background in any direction may be evaluated as an integral involving scalar
and dipole form factors, which incorporate all relevant information about
acoustic oscillations before the time of last scattering. A companion paper
gives asymptotic expressions for the multipole coefficient in terms of
these form factors. Explicit expressions are given here for the form factors in
a simplified hydrodynamic model for the evolution of perturbations.Comment: 35 pages, no figures. Improved treatment of damping, including both
Landau and Silk damping; inclusion of late-time effects; several references
added; minor changes and corrections made. Accepted for publication in Phys.
Rev. D1
Fully nonlinear and exact perturbations of the Friedmann world model
In 1988 Bardeen has suggested a pragmatic formulation of cosmological
perturbation theory which is powerful in practice to employ various fundamental
gauge conditions easily depending on the character of the problem. The
perturbation equations are presented without fixing the temporal gauge
condition and are arranged so that one can easily impose fundamental gauge
conditions by simply setting one of the perturbation variables in the equations
equal to zero. In this way one can use the gauge degrees of freedom as an
advantage in handling problems. Except for the synchronous gauge condition, all
the other fundamental gauge conditions completely fix the gauge mode, and
consequently, each variable in such a gauge has a unique gauge invariant
counterpart, so that we can identify the variable as the gauge-invariant one.
Here, we extend Bardeen's linear formulation to fully nonlinear order in
perturbations, with the gauge advantage kept intact. Derived equations are
exact, and from these we can easily expand to higher order perturbations in a
gauge-ready form. We consider scalar- and vector-type perturbations of an ideal
fluid in a flat background; we also present the multiple components of ideal
fluid case. As applications we present fully nonlinear density and velocity
perturbation equations in Einstein's gravity in the zero-pressure medium,
vorticity generation from pure scalar-type perturbation, and fluid formulation
of a minimally coupled scalar field, all in the comoving gauge. We also present
the equation of gravitational waves generated from pure scalar- and vector-type
perturbations.Comment: 23 pages, to appear in MNRA
Kilohertz-driven Bose-Einstein condensates in optical lattices
We analyze time-of-flight absorption images obtained with dilute
Bose-Einstein con-densates released from shaken optical lattices, both
theoretically and experimentally. We argue that weakly interacting, ultracold
quantum gases in kilohertz-driven optical potentials constitute equilibrium
systems characterized by a steady-state distri-bution of Floquet-state
occupation numbers. Our experimental results consistently indicate that a
driven ultracold Bose gas tends to occupy a single Floquet state, just as it
occupies a single energy eigenstate when there is no forcing. When the driving
amplitude is sufficiently high, the Floquet state possessing the lowest mean
energy does not necessarily coincide with the Floquet state connected to the
ground state of the undriven system. We observe strongly driven Bose gases to
condense into the former state under such conditions, thus providing nontrivial
examples of dressed matter waves.Comment: 36 pages, 3 figures, Advance Atomic Molecular Physics in pres
Multi-scale initial conditions for cosmological simulations
We discuss a new algorithm to generate multi-scale initial conditions with
multiple levels of refinements for cosmological "zoom-in" simulations. The
method uses an adaptive convolution of Gaussian white noise with a real space
transfer function kernel together with an adaptive multi-grid Poisson solver to
generate displacements and velocities following first (1LPT) or second order
Lagrangian perturbation theory (2LPT). The new algorithm achieves RMS relative
errors of order 10^(-4) for displacements and velocities in the refinement
region and thus improves in terms of errors by about two orders of magnitude
over previous approaches. In addition, errors are localized at coarse-fine
boundaries and do not suffer from Fourier-space induced interference ringing.
An optional hybrid multi-grid and Fast Fourier Transform (FFT) based scheme is
introduced which has identical Fourier space behaviour as traditional
approaches. Using a suite of re-simulations of a galaxy cluster halo our real
space based approach is found to reproduce correlation functions, density
profiles, key halo properties and subhalo abundances with per cent level
accuracy. Finally, we generalize our approach for two-component baryon and
dark-matter simulations and demonstrate that the power spectrum evolution is in
excellent agreement with linear perturbation theory. For initial baryon density
fields, it is suggested to use the local Lagrangian approximation in order to
generate a density field for mesh based codes that is consistent with
Lagrangian perturbation theory instead of the current practice of using the
Eulerian linearly scaled densities.Comment: 22 pages, 24 figures. MNRAS in press. Updated affiliation
On the gravitational, dilatonic and axionic radiative damping of cosmic strings
We study the radiation reaction on cosmic strings due to the emission of
dilatonic, gravitational and axionic waves. After verifying the (on average)
conservative nature of the time-symmetric self-interactions, we concentrate on
the finite radiation damping force associated with the half-retarded minus
half-advanced ``reactive'' fields. We revisit a recent proposal of using a
``local back reaction approximation'' for the reactive fields. Using
dimensional continuation as convenient technical tool, we find, contrary to
previous claims, that this proposal leads to antidamping in the case of the
axionic field, and to zero (integrated) damping in the case of the
gravitational field. One gets normal positive damping only in the case of the
dilatonic field. We propose to use a suitably modified version of the local
dilatonic radiation reaction as a substitute for the exact (non-local)
gravitational radiation reaction. The incorporation of such a local
approximation to gravitational radiation reaction should allow one to complete,
in a computationally non-intensive way, string network simulations and to give
better estimates of the amount and spectrum of gravitational radiation emitted
by a cosmologically evolving network of massive strings.Comment: 48 pages, RevTex, epsfig, 1 figure; clarification of the domain of
validity of the perturbative derivation of the string equations of motion,
and of their renormalizabilit
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