75 research outputs found
Brief comments on Jackiw-Teitelboim gravity coupled to Liouville theory
Jackiw-Teitelboim gravity with non-vanishing cosmological constant coupled to
Liouville theory is considered as a non-critical string on dimensional flat
spacetime. It is discussed how the presence of cosmological constant yields
additional constraints on the parameter space of the theory, even when the
conformal anomaly is independent of the cosmological constant. Such constraints
agree with the necessary conditions for the tachyon field to be a primary
--prelogarithmic-- operator of the worldsheet conformal field theory. Thus, the
linearized tachyon field equation allows to impose the diagonal condition for
the interaction term. We analyze the neutralization of the Liouville mode
induced by the coupling to the Jackiw-Teitelboim Lagrangian. The free field
prescription leads to obtain explicit expressions for three-point correlation
functions for the case of vanishing cosmological constant in terms of a product
of Shapiro-Virasoro integrals. This is a consequence of the mentioned
neutralization effect.Comment: 14 pages, no figures. v2 References added. To be published in
Classical and Quantum Gravity. v3 typos correcte
Fitting the Quark and Lepton Masses in String Theories
The capability of string theories to reproduce at low energy the observed
pattern of quark and lepton masses and mixing angles is examined, focusing the
attention on orbifold constructions, where the magnitude of Yukawa couplings
depends on the values of the deformation parameters which describe the size and
shape of the compactified space. A systematic exploration shows that for ,
, --I and possibly orbifolds a correct fit of the physical
fermion masses is feasible. In this way the experimental masses, which are
low--energy quantities, select a particular size and shape of the compactified
space, which turns out to be very reasonable (in particular the modulus
defining the former is ). The rest of the orbifolds are rather
hopeless and should be discarded on the assumption of a minimal scenario. On the other hand, due to stringy selection
rules, there is no possibility of fitting the Kobayashi--Maskawa parameters at
the renormalizable level, although it is remarked that this job might well be
done by non--renormalizable couplings.Comment: 19 page
Dilaton Quantum Cosmology in Two Dimensions
We consider a renormalizable two-dimensional model of dilaton gravity coupled
to a set of conformal fields as a toy model for quantum cosmology. We discuss
the cosmological solutions of the model and study the effect of including the
backreaction due to quantum corrections. As a result, when the matter density
is below some threshold new singularities form in a weak coupling region, which
suggests that they will not be removed in the full quantum theory. We also
solve the Wheeler-DeWitt equation. Depending on the quantum state of the
Universe, the singularities may appear in a quantum region where the wave
function is not oscillatory, i.e., when there is not a well defined notion of
classical spacetime.Comment: 17 pages, UTTG-28-9
On 'Light' Fermions and Proton Stability in 'Big Divisor' D3/D7 Swiss Cheese Phenomenology
Building up on our earlier work [1,2], we show the possibility of generating
"light" fermion mass scales of MeV-GeV range (possibly related to first two
generations of quarks/leptons) as well as eV (possibly related to first two
generations of neutrinos) in type IIB string theory compactified on
Swiss-Cheese orientifolds in the presence of a mobile space-time filling
D3-$brane restricted to (in principle) stacks of fluxed D7-branes wrapping the
"big" divisor \Sigma_B. This part of the paper is an expanded version of the
latter half of section 3 of a published short invited review [3] written up by
one of the authors [AM]. Further, we also show that there are no SUSY GUT-type
dimension-five operators corresponding to proton decay, as well as estimate the
proton lifetime from a SUSY GUT-type four-fermion dimension-six operator to be
10^{61} years. Based on GLSM calculations in [1] for obtaining the geometric
Kaehler potential for the "big divisor", using further the Donaldson's
algorithm, we also briefly discuss in the first of the two appendices,
obtaining a metric for the Swiss-Cheese Calabi-Yau used, that becomes Ricci
flat in the large volume limit.Comment: v2: 1+25 pages, Title modified and text thoroughly expanded including
a brief discussion on obtaining Ricci-flat Swiss Cheese Calabi-Yau metrics
using the Donaldson's algorithm, references added, to appear in EPJ
Finite sigma models and exact string solutions with Minkowski signature metric
We consider sigma models with a - dimensional Minkowski
signature target space metric having a covariantly constant null Killing
vector. These models are UV finite. The -dimensional target space metric
can be explicitly determined for a class of supersymmetric sigma models with
-dimensional `transverse' part of the target space being homogeneous
K\"ahler. The corresponding `transverse' sub-theory is an supersymmetric
sigma model with the exact \gb-function coinciding with its one-loop
expression. For example, the finite model has supersymmetric sigma
model as its `transverse' part. Moreover, there exists a non-trivial dilaton
field such that the Weyl invariance conditions are also satisfied, i.e. the
resulting models correspond to string vacua. Generic solutions are represented
in terms of the RG flow in `transverse' theory. We suggest a possible
application of the constructed Weyl invariant sigma models to quantisation of
gravity. They may be interpreted as `effective actions' of the quantum
dilaton gravity coupled to a (non-conformal) -dimensional `matter'
theory. The conformal factor of the metric and `dilaton' are
identified with the light cone coordinates of the - dimensional sigma
model.Comment: 24 pages, harvmac, Imperial/TP/92-93/
Flavor changing neutral current constraints on standard-like orbifold models
We examine for standard-like orbifold compactification models the constraints
due to quarks and leptons generation non-universality of soft supersymmetry
breaking interactions. We follow the approach initiated by Ibanez and Lust and
developed by Brignole, Ibanez and Munoz. The breaking of supersymmetry is
represented in terms of dilaton and moduli auxiliary field components and,
consistently with a vanishing cosmological constant, is parametrized in terms
of the dilaton-moduli mixing angle and the gravitino mass scale
. The soft breaking interactions (gaugino masses, squarks and sleptons
mass matrices, scalars interactions A and B coupling constants) are calculable
as a function of these parameters and of the discrete set of modular weight
parameters specifying the modular transformation properties of the low-energy
fields. We solve the renormalization group one-loop equations for the full set
of gauge, Yukawa and supersymmetry breaking coupling constants.Comment: 32 page
Revisiting Coupling Selection Rules in Heterotic Orbifold Models
We study L-point couplings between twisted sector fields in heterotic
orbifold compactifications, using conformal field theory. Selection rules
provide an easy way to identify which couplings are non-vanishing. Those used
in the current literature are gauge invariance, R-charge conservation and the
space group selection rule, but they are not the whole story. We revive and
refine a fourth selection rule, due to symmetries in the underlying torus
lattice, and introduce a fifth one, due to the existence or not of classical
worldsheet instanton solutions to mediate the couplings. We consider briefly
the phenomenological consequences of the additional rules, in particular for
recent orbifold constructions whose field content correspond to that of the
MSSM. The structure of the exotic mass matrices is unaltered and many
dimension-5 proton-decay operators vanish.Comment: 27 pages, v2: several clarifications, matches JHEP version. v3:
supercedes journal version, erratum to appear in JHEP; correction to "rule 5"
equations, main ideas unchange
Multiple Sclerosis Susceptibility-Associated SNPs Do Not Influence Disease Severity Measures in a Cohort of Australian MS Patients
Recent association studies in multiple sclerosis (MS) have identified and replicated several single nucleotide polymorphism (SNP) susceptibility loci including CLEC16A, IL2RA, IL7R, RPL5, CD58, CD40 and chromosome 12q13–14 in addition to the well established allele HLA-DR15. There is potential that these genetic susceptibility factors could also modulate MS disease severity, as demonstrated previously for the MS risk allele HLA-DR15. We investigated this hypothesis in a cohort of 1006 well characterised MS patients from South-Eastern Australia. We tested the MS-associated SNPs for association with five measures of disease severity incorporating disability, age of onset, cognition and brain atrophy. We observed trends towards association between the RPL5 risk SNP and time between first demyelinating event and relapse, and between the CD40 risk SNP and symbol digit test score. No associations were significant after correction for multiple testing. We found no evidence for the hypothesis that these new MS disease risk-associated SNPs influence disease severity
The potential role of mitochondrial ATP synthase inhibitory factor 1 (IF1) in coronary heart disease: a literature review
Cardiovascular disease (CVD) is the leading cause of death worldwide, and so the search for innovative and accurate biomarkers for guiding prevention, diagnosis, and treatment is a valuable clinical and economic endeavor. Due to a recent findings that the serum concentration of mitochondrial ATP synthase inhibitory factor 1 (IF1) is an independent prognostic factor in patients with coronary heart disease (CHD), we reviewed the role of this protein in myocardial ischemic preconditioning, its correlation to plasma high density lipoprotein (HDL), the predictive potential in patients with CHD, and its interplay with angiogenesis. IF1 has been positively correlated with plasma HDL-cholesterol, and is independently negatively associated with all-cause and CV mortality in patients with CHD. However, this conclusion is prevalently based on limited data, and more research is needed to draw definitive conclusions. IF1 seems to play an additional role in increasing cell vulnerability in oncologic diseases but may also function as modest inhibitor of angiogenesis in physiological conditions. It has been also explored that IF1 may rather act as a modulator of other molecules more significantly involved in angiogenesis, especially apolipoprotein A1 on which the largest effect could be observed. In conclusion, more research is needed to characterize the role of IF1 in patients with CHD
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