807 research outputs found
Spatial Structures and Giant Number Fluctuations in Models of Active Matter
The large scale fluctuations of the ordered state in active matter systems
are usually characterised by studying the "giant number fluctuations" of
particles in any finite volume, as compared to the expectations from the
central limit theorem. However, in ordering systems, the fluctuations in
density ordering are often captured through their structure functions deviating
from Porod law. In this paper we study the relationship between giant number
fluctuations and structure functions, for different models of active matter as
well as other non-equilibrium systems. A unified picture emerges, with
different models falling in four distinct classes depending on the nature of
their structure functions. For one class, we show that experimentalists may
find Porod law violation, by measuring subleading corrections to the number
fluctuations.Comment: 5 pages, 3 figure
The Reconstruction of Supersymmetric Theories at High Energy Scales
The reconstruction of fundamental parameters in supersymmetric theories
requires the evolution to high scales, where the characteristic regularities in
mechanisms of supersymmetry breaking become manifest. We have studied a set of
representative examples in this context: minimal supergravity and a left--right
symmetric extension; gauge mediated supersymmetry breaking; and superstring
effective field theories. Through the evolution of the parameters from the
electroweak scale the regularities in different scenarios at the high scales
can be unravelled if precision analyses of the supersymmetric particle sector
at e+ e- linear colliders are combined with analyses at the LHC.Comment: 36 pages, latex, 6 figure
Violation of Porod law in a freely cooling granular gas in one dimension
We study a model of freely cooling inelastic granular gas in one dimension,
with a restitution coefficient which approaches the elastic limit below a
relative velocity scale v. While at early times (t << 1/v) the gas behaves as a
completely inelastic sticky gas conforming to predictions of earlier studies,
at late times (t >> 1/v) it exhibits a new fluctuation dominated phase ordering
state. We find distinct scaling behavior for the (i) density distribution
function, (ii) occupied and empty gap distribution functions, (iii) the density
structure function and (iv) the velocity structure function, as compared to the
completely inelastic sticky gas. The spatial structure functions (iii) and (iv)
violate the Porod law. Within a mean-field approximation, the exponents
describing the structure functions are related to those describing the spatial
gap distribution functions.Comment: 4 pages, 5 figure
Majoron emission in muon and tau decays revisited
In models where the breaking of lepton number is spontaneous a massless
Goldstone boson, the Majoron (), appears. We calculate the theoretically
allowed range for the branching ratios of Majoron emitting charged lepton
decays, such as Br() and Br(), in a
supersymmetric model with spontaneous breaking of R-parity. Br() is
maximal in the same region of parameter space for which the lightest neutralino
decays mainly invisibly. A measurement of Br() thus potentially
provides information on R-parity violation complementary to accelerator
searches. We also briefly discuss existing bounds and prospects for future
improvements on the Majoron coupling to charged leptons.Comment: 9 pages, 4 figure
Selectron Pair Production at e-e- and e+e- Colliders with Polarized Beams
We investigate selectron pair production and decay in e-e- scattering and
e+e- annihilation with polarized beams taking into account neutralino mixing as
well as ISR and beamstrahlung corrections. One of the main advantages of having
both modes at disposal is their complementarity concerning the threshold
behaviour of selectron pair production. In e-e- the cross sections at threshold
for seleectron_R selectron_R and selectron_L selectron_L rise proportional to
the momentum of the selectron and in e+ e- that for selectron_R selectron_L.
Measurements at threshold with polarized beams can be used to determine the
selectron masses precisely. Moreover we discuss how polarized electron and
positron beams can be used to establish directly the weak quantum numbers of
the selectrons. We also use selectron pair production to determine the gaugino
mass parameter M_1. This is of particular interest for scenarios with
non-universal gaugino masses at a high scale resulting in |M_1| << |M_2| at the
electroweak scale. Moreover, we consider also the case of a non-vanishing
selectron mixing and demonstrate that it leads to a significant change in the
phenomenology of selectrons.Comment: LaTex, 23 pages, 14 figures, v2, typos corrected, version to appear
in Eur.Phys.J.
R-parity violation: Hide & Seek
We point out that, if R-parity is broken spontaneously, the neutralino can
decay to the final state majoron plus neutrino, which from the experimental
point of view is indistinguishable from the standard missing momentum signal of
supersymmetry. We identify the regions of parameter space where this decay mode
is dominant and show that they are independent of R-parity conserving SUSY
parameters. Thus, (a) only very weak limits on R-parity violating couplings can
be derived from the observation of missing momentum events and (b) at future
collider experiments huge statistics might be necessary to establish that
R-parity indeed is broken. Parameter combinations which give calculated relic
neutralino density larger than the measured dark matter density in case of
conserved R-parity are valid points in this scenario and their phenomenology at
the LHC deserves to be studied.Comment: 8 pages, 2 figures; ref. added; matches published version (title
changed in the published version
Uncertainties in Relic Density Calculations in mSUGRA
We compare the relic density of neutralino dark matter within the minimal
supergravity model (mSUGRA) using four different public codes for
supersymmetric spectra evaluation. While the predictions for the relic density
of neutralinos are rather stable in most of the mSUGRA space, it is in the most
physically interesting regions that large discrepancies can be observed, in
particular the focus point, large tan beta and coannihilation regions.Comment: 6 pages, 3 figure
Analysis of enhanced tan(beta) corrections in MFV GUT scenarios
We analyse a minimal supersymmetric standard model (MSSM) taking a minimal
flavour violation (MFV) structure at the GUT scale. We evaluate the parameters
at the electroweak scale taking into account the full flavour structure in the
evolution of the renormalization group equations. We concentrate mainly on the
decay Bs -> mu mu and its correlations with other observables like b -> s
gamma, b -> s l l, Delta M_Bs and the anomalous magnetic moment of the muon. We
restrict our analysis to the regions in parameter space consistent with the
dark matter constraints. We find that the BR(Bs -> mu mu) can exceed the
current experimental limit in the regions of parameter space which are allowed
by all other constraints thus providing an additional bound on supersymmetric
parameters. This holds even in the constrained MSSM. Assuming an hypothetical
measurement of BR(Bs -> mu mu) ~ 10^-7 we analyse the predicted MSSM spectrum
and flavour violating decay modes of supersymmetric particles which are found
to be small.Comment: 47 pages, 16 figures (best viewed printed or in pdf format), updated
lattice inputs used, version submitted to PR
Reconstructing Supersymmetry at ILC/LHC
Coherent analyses of experimental results from LHC and ILC will allow us to
draw a comprehensive and precise picture of the supersymmetric particle sector.
Based on this platform the fundamental supersymmetric theory can be
reconstructed at the high scale which is potentially close to the Planck scale.
This procedure will be reviewed for three characteristic examples: minimal
supergravity as the paradigm; a left-right symmetric extension incorporating
intermediate mass scales; and a specific realization of string effective
theories.Comment: published in Proceedings of the Ustron Conference 2005; technical
LaTeX problem correcte
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