343 research outputs found
Spectral Analysis of Multi-dimensional Self-similar Markov Processes
In this paper we consider a discrete scale invariant (DSI) process with scale . We consider to have some fix number of
observations in every scale, say , and to get our samples at discrete points
where is obtained by the equality
and . So we provide a discrete time scale
invariant (DT-SI) process with parameter space . We find the spectral representation of the covariance function of
such DT-SI process. By providing harmonic like representation of
multi-dimensional self-similar processes, spectral density function of them are
presented. We assume that the process is also Markov
in the wide sense and provide a discrete time scale invariant Markov (DT-SIM)
process with the above scheme of sampling. We present an example of DT-SIM
process, simple Brownian motion, by the above sampling scheme and verify our
results. Finally we find the spectral density matrix of such DT-SIM process and
show that its associated -dimensional self-similar Markov process is fully
specified by where is
the covariance function of th and th observations of the process.Comment: 16 page
Coupling running through the Looking-Glass of dimensional Reduction
The dimensional reduction, in a form of transition from four to two
dimensions, was used in the 90s in a context of HE Regge scattering. Recently,
it got a new impetus in quantum gravity where it opens the way to
renormalizability and finite short-distance behavior. We consider a QFT model
with running coupling defined in both the two domains of
different dimensionality; the \gbar(Q^2)\, evolutions being duly conjugated
at the reduction scale Beyond this scale, in the deep UV 2-dim
region, the running coupling does not increase any more. Instead, it {\it
slightly decreases} and tends to a finite value \gbar_2(\infty) \,< \,
\gbar_2(M^2)\, from above. As a result, the global evolution picture looks
quite peculiar and can propose a base for the modified scenario of gauge
couplings behavior with UV fixed points provided by dimensional reduction
instead of leptoquarks.Comment: 8 pages, 4 figures,Version to match the one which (besides the
Appendix) will appear in "Particles and Nuclei (PEPAN), Letters", v.7, No
6(162) 2010 pp 625-631. Slightly edited, one more reference and related
numerical estimate adde
Non-universal gaugino masses: a signal-based analysis for the Large Hadron Collider
We discuss the signals at the Large Hadron Collider (LHC) for scenarios with
non-universal gaugino masses in supersymmetric (SUSY) theories. We perform a
multichannel analysis, and consider the ratios of event rates in different
channels such as , - and -
, as well as and final states
together with . Low-energy SUSY spectra corresponding to
high-scale gaugino non-universality arising from different breaking schemes of
SU(5) as well as SO(10) Grand Unified (GUT) SUSY models are considered, with
both degenerate low-energy sfermion masses and those arising from a
supergravity scenario. We present the numerical predictions over a wide range
of the parameter space using the event generator {\tt Pythia}, specifying the
event selection criteria and pointing out regions where signals are likely to
be beset with backgrounds. Certain broad features emerge from the study, which
may be useful in identifying the signatures of different GUT breaking schemes
and distinguishing them from a situation with a universal gaugino mass at high
scale. The absolute values of the predicted event rates for different scenarios
are presented together with the various event ratios, so that these can also be
used whenever necessary.Comment: 54 pages, 18 figure
Fast optical variability of SS 433
We study the optical variability of the peculiar Galactic source SS 433 using
the observations made with the Russian Turkish 1.5-m telescope (RTT150). A
simple technique which allows to obtain high-quality photometric measurements
with 0.3-1 s time resolution using ordinary CCD is described in detail. Using
the test observations of nonvariable stars, we show that the atmospheric
turbulence introduces no significant distortions into the measured light
curves. Therefore, the data obtained in this way are well suited for studying
the aperiodic variability of various objects.
The large amount of SS 433 optical light curve measurements obtained in this
way allowed us to obtain the power spectra of its flux variability with a
record sensitivity up to frequencies of ~0.5 Hz and to detect its break at
frequency =~2.4e-3 Hz. We suggest that this break in the power spectrum results
from the smoothing of the optical flux variability due to a finite size of the
emitting region. Based on our measurement of the break frequency in the power
spectrum, we estimated the size of the accretion-disk photosphere as 2e12 cm.
We show that the amplitude of the variability in SS 433 decreases sharply
during accretion-disk eclipses, but it does not disappear completely. This
suggests that the size of the variable optical emission source is comparable to
that of the normal star whose size is therefore R_O \approx 2e12 cm \approx 30
R_sun. The decrease in flux variability amplitude during eclipses suggests the
presence of a nonvariable optical emission component with a magnitude
m_R=~13.2.Comment: 12 pages, 11 figures. Accepted for publication in Astronomy Letters.
The original version in Russian is available at
http://hea.iki.rssi.ru/rtt150/ru/ss433_pazh10/pss433_fast.pd
Unit roots in periodic autoregressions
Abstract. This paper analyzes the presence and consequences of a unit root in periodic autoregressive models for univariate quarterly time series. First, we consider various representations of such models, including a new parametrization which facilitates imposing a unit root restriction. Next, we propose a class of likelihood ratio tests for a unit root, and we derive their asymptotic null distributions. Likelihood ratio tests for periodic parameter variation are also proposed. Finally, we analyze the impact on unit root inference of misspecifying a periodic process by a constant-parameter model
Adiabatic compression and indirect detection of supersymmetric dark matter
Recent developments in the modelling of the dark matter distribution in our
Galaxy point out the necessity to consider some physical processes to satisfy
observational data. In particular, models with adiabatic compression, which
include the effect of the baryonic gas in the halo, increase significantly the
dark matter density in the central region of the Milky Way. On the other hand,
the non-universality in scalar and gaugino sectors of supergravity models can
also increase significantly the neutralino annihilation cross section. We show
that the combination of both effects gives rise to a gamma-ray flux arising
from the Galactic Center largely reachable by future experiments like GLAST. We
also analyse in this framework the EGRET excess data above 1 GeV, as well as
the recent data from CANGAROO and HESS. The analysis has been carried out
imposing the most recent experimental constraints, such as the lower bound on
the Higgs mass, the \bsg branching ratio, and the muon . In addition, the
recently improved upper bound on has also been taken
into account. The astrophysical (WMAP) bounds on the dark matter density have
also been imposed on the theoretical computation of the relic neutralino
density through thermal production.Comment: 32 pages, 11 figures, final version to appear in JCA
Two photon annihilation of Kaluza-Klein dark matter
We investigate the fermionic one-loop cross section for the two photon
annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal
extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray
line with energy equal to the KK dark matter particle mass. We find that the
cross section is large enough that if a continuum signature is detected, the
energy distribution of gamma-rays should end at the particle mass with a peak
that is visible for an energy resolution of the detector at the percent level.
This would give an unmistakable signature of a dark matter origin of the
gamma-rays, and a unique determination of the dark matter particle mass, which
in the case studied should be around 800 GeV. Unlike the situation for
supersymmetric models where the two-gamma peak may or may not be visible
depending on parameters, this feature seems to be quite robust in UED models,
and should be similar in other models where annihilation into fermions is not
helicity suppressed. The observability of the signal still depends on largely
unknown astrophysical parameters related to the structure of the dark matter
halo. If the dark matter near the galactic center is adiabatically contracted
by the central star cluster, or if the dark matter halo has substructure
surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio
Oscillatory Fractional Brownian Motion and Hierarchical Random Walks
We introduce oscillatory analogues of fractional Brownian motion,
sub-fractional Brownian motion and other related long range dependent Gaussian
processes, we discuss their properties, and we show how they arise from
particle systems with or without branching and with different types of initial
conditions, where the individual particle motion is the so-called c-random walk
on a hierarchical group. The oscillations are caused by the discrete and
ultrametric structure of the hierarchical group, and they become slower as time
tends to infinity and faster as time approaches zero. We also give other
results to provide an overall picture of the behavior of this kind of systems,
emphasizing the new phenomena that are caused by the ultrametric structure as
compared with results for analogous models on Euclidean space
Stable Isotope Composition of Fatty Acids in Organisms of Different Trophic Levels in the Yenisei River
We studied four-link food chain, periphytic microalgae and water moss (producers), trichopteran larvae (consumers I), gammarids (omnivorous – consumers II) and Siberian grayling (consumers III) at a littoral site of the Yenisei River on the basis of three years monthly sampling. Analysis of bulk carbon stable isotopes and compound specific isotope analysis of fatty acids (FA) were done. As found, there was a gradual depletion in 13C contents of fatty acids, including essential FA upward the food chain. In all the trophic levels a parabolic dependence of δ13C values of fatty acids on their degree of unsaturation/chain length occurred, with 18:2n-6 and 18:3n-3 in its lowest point. The pattern in the δ13C differences between individual fatty acids was quite similar to that reported in literature for marine pelagic food webs. Hypotheses on isotope fractionation were suggested to explain the findings
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