1,568 research outputs found
Introduction to a Biological Systems Science
Biological systems analysis and biodynamic modelling of physiological and biological interrelationships in human body and mammal
On the electroweak phase transition in the Minimal Supersymmetric Standard Model
We study the finite-temperature effective potential of the Minimal
Supersymmetric Standard Model, in the limit of only one light Higgs boson.
Because of the large top Yukawa coupling, there can be significant differences
with respect to the Standard Model case: for given values of the Higgs and top
masses, little supersymmetry breaking in the stop sector can make the phase
transition more strongly first-order. After including the full structure of the
stop mass matrix, the most important experimental constraints and the leading
plasma effects, we find that the present limits on Higgs and squark masses are
still compatible with the scenario of electroweak baryogenesis, in a small
region of parameter space corresponding to m_h \simlt 70 \gev and \msba
\simlt 105 \gev.Comment: 10 A4 pages, 7 figures available upon request, CERN-TH.6833/93,
IEM-FT-69/93 (one paragraph expanded for clarity
Submanifolds in five-dimensional pseudo-Euclidean spaces and four-dimensional FRW universes
Equations for submanifolds, which correspond to embeddings of the
four-dimensional FRW universes in five-dimensional pseudo-Euclidean spaces, are
presented in convenient form in general case. Several specific examples are
considered.Comment: 7 pages, LaTeX, the mathematical part of this paper is based on the
withdrawn preprint arXiv:1012.0320 [gr-qc
New Constraints (and Motivations) for Abelian Gauge Bosons in the MeV-TeV Mass Range
We survey the phenomenological constraints on abelian gauge bosons having
masses in the MeV to multi-GeV mass range (using precision electroweak
measurements, neutrino-electron and neutrino-nucleon scattering, electron and
muon anomalous magnetic moments, upsilon decay, beam dump experiments, atomic
parity violation, low-energy neutron scattering and primordial
nucleosynthesis). We compute their implications for the three parameters that
in general describe the low-energy properties of such bosons: their mass and
their two possible types of dimensionless couplings (direct couplings to
ordinary fermions and kinetic mixing with Standard Model hypercharge). We argue
that gauge bosons with very small couplings to ordinary fermions in this mass
range are natural in string compactifications and are likely to be generic in
theories for which the gravity scale is systematically smaller than the Planck
mass - such as in extra-dimensional models - because of the necessity to
suppress proton decay. Furthermore, because its couplings are weak, in the
low-energy theory relevant to experiments at and below TeV scales the charge
gauged by the new boson can appear to be broken, both by classical effects and
by anomalies. In particular, if the new gauge charge appears to be anomalous,
anomaly cancellation does not also require the introduction of new light
fermions in the low-energy theory. Furthermore, the charge can appear to be
conserved in the low-energy theory, despite the corresponding gauge boson
having a mass. Our results reduce to those of other authors in the special
cases where there is no kinetic mixing or there is no direct coupling to
ordinary fermions, such as for recently proposed dark-matter scenarios.Comment: 49 pages + appendix, 21 figures. This is the final version which
appears in JHE
Effective Theory Approach to the Spontaneous Breakdown of Lorentz Invariance
We generalize the coset construction of Callan, Coleman, Wess and Zumino to
theories in which the Lorentz group is spontaneously broken down to one of its
subgroups. This allows us to write down the most general low-energy effective
Lagrangian in which Lorentz invariance is non-linearly realized, and to explore
the consequences of broken Lorentz symmetry without having to make any
assumptions about the mechanism that triggers the breaking. We carry out the
construction both in flat space, in which the Lorentz group is a global
spacetime symmetry, and in a generally covariant theory, in which the Lorentz
group can be treated as a local internal symmetry. As an illustration of this
formalism, we construct the most general effective field theory in which the
rotation group remains unbroken, and show that the latter is just the
Einstein-aether theory.Comment: 45 pages, no figures
New physics searches at near detectors of neutrino oscillation experiments
We systematically investigate the prospects of testing new physics with tau
sensitive near detectors at neutrino oscillation facilities. For neutrino beams
from pion decay, from the decay of radiative ions, as well as from the decays
of muons in a storage ring at a neutrino factory, we discuss which effective
operators can lead to new physics effects. Furthermore, we discuss the present
bounds on such operators set by other experimental data currently available.
For operators with two leptons and two quarks we present the first complete
analysis including all relevant operators simultaneously and performing a
Markov Chain Monte Carlo fit to the data. We find that these effects can induce
tau neutrino appearance probabilities as large as O(10^{-4}), which are within
reach of forthcoming experiments. We highlight to which kind of new physics a
tau sensitive near detector would be most sensitive.Comment: 20 pages, 2 figures, REVTeX
Non-standard interactions versus non-unitary lepton flavor mixing at a neutrino factory
The impact of heavy mediators on neutrino oscillations is typically described
by non-standard four-fermion interactions (NSIs) or non-unitarity (NU). We
focus on leptonic dimension-six effective operators which do not produce
charged lepton flavor violation. These operators lead to particular
correlations among neutrino production, propagation, and detection non-standard
effects. We point out that these NSIs and NU phenomenologically lead, in fact,
to very similar effects for a neutrino factory, for completely different
fundamental reasons. We discuss how the parameters and probabilities are
related in this case, and compare the sensitivities. We demonstrate that the
NSIs and NU can, in principle, be distinguished for large enough effects at the
example of non-standard effects in the --sector, which basically
corresponds to differentiating between scalars and fermions as heavy mediators
as leading order effect. However, we find that a near detector at superbeams
could provide very synergistic information, since the correlation between
source and matter NSIs is broken for hadronic neutrino production, while NU is
a fundamental effect present at any experiment.Comment: 32 pages, 5 figures. Final version published in JHEP. v3: Typo in Eq.
(27) correcte
Fungal iron availability during deep seated candidiasis is defined by a complex interplay involving systemic and local events
Peer reviewedPublisher PD
Neutrinoless double beta decay in seesaw models
We study the general phenomenology of neutrinoless double beta decay in
seesaw models. In particular, we focus on the dependence of the neutrinoless
double beta decay rate on the mass of the extra states introduced to account
for the Majorana masses of light neutrinos. For this purpose, we compute the
nuclear matrix elements as functions of the mass of the mediating fermions and
estimate the associated uncertainties. We then discuss what can be inferred on
the seesaw model parameters in the different mass regimes and clarify how the
contribution of the light neutrinos should always be taken into account when
deriving bounds on the extra parameters. Conversely, the extra states can also
have a significant impact, cancelling the Standard Model neutrino contribution
for masses lighter than the nuclear scale and leading to vanishing neutrinoless
double beta decay amplitudes even if neutrinos are Majorana particles. We also
discuss how seesaw models could reconcile large rates of neutrinoless double
beta decay with more stringent cosmological bounds on neutrino masses.Comment: 34 pages, 5 eps figures and 1 axodraw figure. Final version published
in JHEP. NME results available in Appendi
PGB pair production at LHC and ILC as a probe of the topcolor-assisted technicolor models
The topcolor-assisted technicolor (TC2) model predicts some light pseudo
goldstone bosons (PGBs), which may be accessible at the LHC or ILC. In this
work we study the pair productions of the charged or neutral PGBs at the LHC
and ILC. For the productions at the LHC we consider the processes proceeding
through gluon-gluon fusion and quark-antiquark annihilation, while for the
productions at the ILC we consider both the electron-positron collision and the
photon-photon collision. We find that in a large part of parameter space the
production cross sections at both colliders can be quite large compared with
the low standard model backgrounds. Therefore, in future experiments these
productions may be detectable and allow for probing TC2 model.Comment: 26 pages, 16 figures. slight changes in the text; notations for
curves changed; references adde
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