43,476 research outputs found
Growing interfaces uncover universal fluctuations behind scale invariance
Stochastic motion of a point -- known as Brownian motion -- has many
successful applications in science, thanks to its scale invariance and
consequent universal features such as Gaussian fluctuations. In contrast, the
stochastic motion of a line, though it is also scale-invariant and arises in
nature as various types of interface growth, is far less understood. The two
major missing ingredients are: an experiment that allows a quantitative
comparison with theory and an analytic solution of the Kardar-Parisi-Zhang
(KPZ) equation, a prototypical equation for describing growing interfaces. Here
we solve both problems, showing unprecedented universality beyond the scaling
laws. We investigate growing interfaces of liquid-crystal turbulence and find
not only universal scaling, but universal distributions of interface positions.
They obey the largest-eigenvalue distributions of random matrices and depend on
whether the interface is curved or flat, albeit universal in each case. Our
exact solution of the KPZ equation provides theoretical explanations.Comment: 5 pages, 3 figures, supplementary information available on Journal
pag
Non Supersymmetric Metastable Vacua in N=2 SYM Softly Broken to N=1
We find non-supersymmetric metastable vacua in four dimensional N=2 gauge
theories softly broken to N=1 by a superpotential term. First we study the
simplest case, namely the SU(2) gauge theory without flavors. We study the
spectrum and lifetime of the metastable vacuum and possible embeddings of the
model in UV complete theories. Then we consider larger gauge group theories
with flavors. We show that when we softly break them to N=1, the potential
induced on specific submanifolds of their moduli space is identical to the
potential in lower rank gauge theories. Then we show that the potential
increases when we move away from this submanifold, allowing us to construct
metastable vacua on them in the theories that can be reduced to the SU(2) case.Comment: 29 pages, 10 figure
Can sacrificial feeding areas protect aquatic plants from herbivore grazing? Using behavioural ecology to inform wildlife management
Effective wildlife management is needed for conservation, economic and human well-being objectives. However, traditional population control methods are frequently ineffective, unpopular with stakeholders, may affect non-target species, and can be both expensive and impractical to implement. New methods which address these issues and offer effective wildlife management are required. We used an individual-based model to predict the efficacy of a sacrificial feeding area in preventing grazing damage by mute swans (Cygnus olor) to adjacent river vegetation of high conservation and economic value. The accuracy of model predictions was assessed by a comparison with observed field data, whilst prediction robustness was evaluated using a sensitivity analysis. We used repeated simulations to evaluate how the efficacy of the sacrificial feeding area was regulated by (i) food quantity, (ii) food quality, and (iii) the functional response of the forager. Our model gave accurate predictions of aquatic plant biomass, carrying capacity, swan mortality, swan foraging effort, and river use. Our model predicted that increased sacrificial feeding area food quantity and quality would prevent the depletion of aquatic plant biomass by swans. When the functional response for vegetation in the sacrificial feeding area was increased, the food quantity and quality in the sacrificial feeding area required to protect adjacent aquatic plants were reduced. Our study demonstrates how the insights of behavioural ecology can be used to inform wildlife management. The principles that underpin our model predictions are likely to be valid across a range of different resource-consumer interactions, emphasising the generality of our approach to the evaluation of strategies for resolving wildlife management problems
Asymptotic Regge Trajectories of Non-strange Mesons
We analyze the asymptotic behavior of Regge trajectories of non-strange
mesons. In contrast to an existing belief, it is demonstrated that for the
asymptotically linear Regge trajectories the width of heavy hadrons cannot
linearly depend on their mass. Using the data on masses and widths of rho_J,
omega_J, a_J and f_J mesons for the spin values J \leq 6, we extract the
parameters of the asymptotically linear Regge trajectory predicted by the
finite width model of quark gluon bags. As it is shown the obtained parameters
for the data set B correspond to the cross-over temperature lying in the
interval 170.9-175.3 MeV which is consistent with the kinetic freeze-out
temperature of early hadronizing particles found in relativistic heavy ion
collisions at and above the highest SPS energy.Comment: 14 pages, 3 figure
Soft Spectrum in Yukawa-Gauge Mediation
We introduce a model independent parametrization for a subclass of gauge
mediated theories, which we refer to as Yukawa-gauge mediation. Within this
formalism we study the resulting soft masses in the visible spectrum. We find
general expressions for the gaugino and scalar masses. Under generic
conditions, the gaugino mass is screened, vanishing at first order in the SUSY
breaking scale.Comment: 22 pages, 4 figures; v2: minor corrections, published versio
Charge qubit dynamics in a double quantum dot coupled to phonons
The dynamics of charge qubit in a double quantum dot coupled to phonons is
investigated theoretically in terms of a perturbation treatment based on a
unitary transformation. The dynamical tunneling current is obtained explicitly.
The result is compared with the standard perturbation theory at Born-Markov
approximation. The decoherence induced by acoustic phonons is analyzed at
length. It is shown that the contribution from deformation potential coupling
is comparable to that from piezoelectric coupling in small dot size and large
tunneling rate case. A possible decoupling mechanism is predicted.Comment: 8 pages, 6 figure
Hidden local symmetry and color confinement
The hidden local symmetry is a successful model to describe the properties of
the vector mesons in QCD. We point out that if we identify this hidden gauge
theory as the magnetic picture of QCD, a linearized version of the model
simultaneously describes color confinement and chiral symmetry breaking. We
demonstrate that such a structure can be seen in the Seiberg dual picture of a
softly broken supersymmetric QCD. The model possesses exact chiral symmetry and
reduces to QCD when mass parameters are taken to be large. Working in the
regime of the small mass parameters, we show that there is a vacuum where
chiral symmetry is spontaneously broken and simultaneously the magnetic gauge
group is Higgsed. If the vacuum we find persists in the limit of large mass
parameters, one can identify the rho meson as the massive magnetic gauge boson,
that is an essential ingredient for color confinement.Comment: 20 pages, 3 figure
The Minimal Scale Invariant Extension of the Standard Model
We perform a systematic analysis of an extension of the Standard Model that
includes a complex singlet scalar field and is scale invariant at the tree
level. We call such a model the Minimal Scale Invariant extension of the
Standard Model (MSISM). The tree-level scale invariance of the model is
explicitly broken by quantum corrections, which can trigger electroweak
symmetry breaking and potentially provide a mechanism for solving the gauge
hierarchy problem. Even though the scale invariant Standard Model is not a
realistic scenario, the addition of a complex singlet scalar field may result
in a perturbative and phenomenologically viable theory. We present a complete
classification of the flat directions which may occur in the classical scalar
potential of the MSISM. After calculating the one-loop effective potential of
the MSISM, we investigate a number of representative scenarios and determine
their scalar boson mass spectra, as well as their perturbatively allowed
parameter space compatible with electroweak precision data. We discuss the
phenomenological implications of these scenarios, in particular, whether they
realize explicit or spontaneous CP violation, neutrino masses or provide dark
matter candidates. In particular, we find a new minimal scale-invariant model
of maximal spontaneous CP violation which can stay perturbative up to
Planck-mass energy scales, without introducing an unnaturally large hierarchy
in the scalar-potential couplings.Comment: 71 pages, 34 eps figures, numerical error corrected, clarifying
comments adde
Interleaved Parton Showers and Tuning Prospects
General-purpose Monte Carlo event generators have become important tools in
particle physics, allowing the simulation of exclusive hadronic final states.
In this article we examine the Pythia 8 generator, in particular focusing on
its parton-shower algorithms. Some relevant new additions to the code are
introduced, that should allow for a better description of data. We also
implement and compare with 2 to 3 real-emission QCD matrix elements, to check
how well the shower algorithm fills the phase space away from the soft and
collinear regions. A tuning of the generator to Tevatron data is performed for
two PDF sets and the impact of first new LHC data is examined
- …