8,975 research outputs found
Quasi-Fixed Points and Charge and Colour Breaking in Low Scale Models
We show that the current LEP2 lower bound upon the minimal supersymmetric
standard model (MSSM) lightest Higgs mass rules out quasi-fixed scenarios for
string scales between 10^6 and 10^{11} GeV unless the heaviest stop mass is
more than 2 TeV. We consider the implications of the low string scale for
charge and colour breaking (CCB) bounds in the MSSM, and demonstrate that CCB
bounds from F and D-flat directions are significantly weakened. For scales less
than 10^{10} GeV these bounds become merely that degenerate scalar mass squared
values are positive at the string scale.Comment: 17 pages, 4 figures. Replacement has added discussion on errors due
to alpha_s(MZ) errors, as well as deviations from the quasi-fixed point. Text
has been clarifie
Brane Gases on K3 and Calabi-Yau Manifolds
We initiate the study of Brane Gas Cosmology (BGC) on manifolds with
non-trivial holonomy. Such compactifications are required within the context of
superstring theory in order to make connections with realistic particle
physics. We study the dynamics of brane gases constructed from various string
theories on background spaces having a K3 submanifold. The K3 compactifications
provide a stepping stone for generalising the model to the case of a full
Calabi-Yau three-fold. Duality symmetries are discussed within a cosmological
context. Using a duality, we arrive at an N=2 theory in four-dimensions
compactified on a Calabi-Yau manifold with SU(3) holonomy. We argue that the
Brane Gas model compactified on such spaces maintains the successes of the
trivial toroidal compactification while greatly enhancing its connection to
particle physics. The initial state of the universe is taken to be a small, hot
and dense gas of p-branes near thermal equilibrium. The universe has no initial
singularity and the dynamics of string winding modes allow three spatial
dimensions to grow large, providing a possible solution to the dimensionality
problem of string theory.Comment: 26 pages; Significant revisions: review material truncated;
presentation improve
Determination of step rate thresholds corresponding to physical activity intensity classifications in adults
Current recommendations call for adults to be physically active at moderate and/or vigorous intensities. Given the popularity of walking and running, the use of step rates may provide a practical and inexpensive means to evaluate ambulatory intensity. Thus, the purpose of this study was to identify step rate thresholds that correspond to various intensity classifications. Methods: Oxygen consumption was measured at rest and during 10 minute treadmill walking and running trials at 6 standardized speeds (54, 80, 107, 134,
161, and 188 mâmin-1) in 9 men and 10 women (28.8 ± 6.8 yrs). Two observers counted the participantsâ steps
at each treadmill speed. Linear and nonlinear regression analyses were used to develop prediction equations
to ascertain step rate thresholds at various intensities. Results: Nonlinear regression analysis of the metabolic
cost versus step rates across all treadmill speeds yielded the highest R2 values for men (R2 = .91) and women
(R2 = .79). For men, the nonlinear analysis yielded 94 and 125 stepâmin-1 for moderate and vigorous intensities,
respectively. For women, 99 and 135 stepâmin-1 corresponded with moderate and vigorous intensities, respectively. Conclusions: Promoting a step rate of 100 stepâmin-1 may serve as a practical public health recommendation to exercise at moderate intensity
Effects of a feeding strategy to increase intramuscular fat content of pork under the conditions of organic farming
In an ongoing study, the effect of the implementation of a specific feeding strategy using a high portion of home-grown grain legumes on the intramuscular fat (IMF) content of pork, is assessed under different conditions on organic farms in Germany and Austria. Preliminary results indicate that variation in the IMF content seems to be higher between farms than between treatments within each farm
On the Thermal History of Calculable Gauge Mediation
Many messenger models with realistic gaugino masses are based on meta-stable
vacua. In this work we study the thermal history of some of these models.
Analyzing R-symmetric models, we point out that while some of the known
messenger models clearly prefer the supersymmetric vacuum, there is a vast
class of models where the answer depends on the initial conditions. Along with
the vacuum at the origin, the high temperature thermal potential also possesses
a local minimum far away from the origin. This vacuum has no analog at zero
temperature. The first order phase transition from this vacuum into the
supersymmetric vacuum is parametrically suppressed, and the theory, starting
from that vacuum, is likely to evolve to the desired gauge-mediation vacuum. We
also comment on the thermal evolution of models without R-symmetry.Comment: 22 pages. V2: Comments on the SM effects added. Minor corrections.
Reference added. Valuable discussion with S. Abel, J. Jaeckel and V. Khoze
acknowledged. V3: Types of EOGM explicitly defined in the introduction.
Discussions about the phase transitions expanded. Typo corrected. Journal
versio
Meta-stable SUSY Breaking Model in Supergravity
We analyze a supersymmetry (SUSY) breaking model proposed by Intriligator,
Seiberg and Shih in a supergravity (SUGRA) framework. This is a simple and
natural setup which demands neither extra superpotential interactions nor an
additional gauge symmetry. In the SUGRA setup, the U(1)R symmetry is explicitly
broken by the constant term in the superpotential, and pseudo-moduli field
naturally takes non-zero vacuum expectation value through a vanishing
cosmological constant condition. Sfermions tend to be heavier than gauginos,
and the strong-coupling scale is determined once a ratio of sfermion to gaugino
masses is fixed.Comment: 13 page
R-symmetry and Supersymmetry Breaking at Finite Temperature
We analyze the spontaneous symmetry breaking at finite temperature
for the simple O'Raifeartaigh-type model introduced in [1] in connection with
spontaneous supersymmetry breaking. We calculate the finite temperature
effective potential (free energy) to one loop order and study the thermal
evolution of the model. We find that the R-symmetry breaking occurs through a
second order phase transition. Its associated meta-stable supersymmetry
breaking vacuum is thermodynamically favored at high temperatures and the model
remains trapped in this state by a potential barrier, as the temperature lowers
all the way until T=0.Comment: 19 pages, 4 figures - Minor revisions, references added. To appear in
JHE
WKB formalism and a lower limit for the energy eigenstates of bound states for some potentials
In the present work the conditions appearing in the WKB approximation
formalism of quantum mechanics are analyzed. It is shown that, in general, a
careful definition of an approximation method requires the introduction of two
length parameters, one of them always considered in the text books on quantum
mechanics, whereas the second one is usually neglected. Afterwards we define a
particular family of potentials and prove, resorting to the aforementioned
length parameters, that we may find an energy which is a lower bound to the
ground energy of the system. The idea is applied to the case of a harmonic
oscillator and also to a particle freely falling in a homogeneous gravitational
field, and in both cases the consistency of our method is corroborated. This
approach, together with the Rayleigh--Ritz formalism, allows us to define an
energy interval in which the ground energy of any potential, belonging to our
family, must lie.Comment: Accepted in Modern Physics Letters
Multiscale Gyrokinetics for Rotating Tokamak Plasmas: Fluctuations, Transport and Energy Flows
This paper presents a complete theoretical framework for plasma turbulence
and transport in tokamak plasmas. The fundamental scale separations present in
plasma turbulence are codified as an asymptotic expansion in the ratio of the
gyroradius to the equilibrium scale length. Proceeding order-by-order in this
expansion, a framework for plasma turbulence is developed. It comprises an
instantaneous equilibrium, the fluctuations driven by gradients in the
equilibrium quantities, and the transport-timescale evolution of mean profiles
of these quantities driven by the fluctuations. The equilibrium distribution
functions are local Maxwellians with each flux surface rotating toroidally as a
rigid body. The magnetic equillibrium is obtained from the Grad-Shafranov
equation for a rotating plasma and the slow (resistive) evolution of the
magnetic field is given by an evolution equation for the safety factor q.
Large-scale deviations of the distribution function from a Maxwellian are given
by neoclassical theory. The fluctuations are determined by the high-flow
gyrokinetic equation, from which we derive the governing principle for
gyrokinetic turbulence in tokamaks: the conservation and local cascade of free
energy. Transport equations for the evolution of the mean density, temperature
and flow velocity profiles are derived. These transport equations show how the
neoclassical corrections and the fluctuations act back upon the mean profiles
through fluxes and heating. The energy and entropy conservation laws for the
mean profiles are derived. Total energy is conserved and there is no net
turbulent heating. Entropy is produced by the action of fluxes flattening
gradients, Ohmic heating, and the equilibration of mean temperatures. Finally,
this framework is condensed, in the low-Mach-number limit, to a concise set of
equations suitable for numerical implementation.Comment: 113 pages, 3 figure
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