9,993 research outputs found
Existence of Double Vortex Solutions
We show analytically and numerically the existence of double vortex solutions
in two-Higgs systems. These solutions are generalizations of the \no vortices
and exist for all values of the parameters in the Lagrangians considered.
We derive analytically the asymptotic behavior of the solutions and confirm
it numerically by solving the field equations.
Finally, we show that these solutions can be embedded in realistic theories
like the two-doublet extension of the standard model.Comment: 10 pages plus 2 figures, use latex. To appear in Phys. Lett. B.
Preprint No. CfA-370
Moduli Inflation from Dynamical Supersymmetry Breaking
Moduli fields, which parameterize perturbative flat directions of the
potential in supersymmetric theories, are natural candidates to act as
inflatons. An inflationary potential on moduli space can result if the scale of
dynamical SUSY breaking in some sector of the theory is determined by a moduli
dependent coupling. The magnitude of density fluctuations generated during
inflation then depends on the scale of SUSY breaking in this sector. This can
naturally be hierarchically smaller than the Planck scale in a dynamical model,
giving small fluctuations without any fine tuning of parameters. It is also
natural for SUSY to be restored at the minimum of the moduli potential, and to
leave the universe with zero cosmological constant after inflation. Acceptable
reheating can also be achieved in this scenario.Comment: 14 pages, latex, improved discussion of reheating for composite
inflaton
Dynamical mass matrices from effective superstring theories
We analyze the general structure of the fermion mass matrices in effective
superstrings. They are generically given at low energy by non-trivial functions
of the gauge singlet moduli fields. Interesting structures appear in particular
if they are homogeneous functions of zero degree in the moduli. In this case we
find Yukawa matrices very similar to the ones obtained by imposing a
family symmetry to reproduce the observed hierarchy of masses and mixing
angles. The role of the symmetry is played here by the modular symmetry.
Explicit orbifold examples are given where realistic quark mass matrices can be
obtained. Finally, a complete scenario is proposed which generates the observed
hierarchies in a dynamical way.Comment: 27 pages, latex, no figure
Determining neutron star masses with weak microlensing
The masses of stars including stellar remnants are almost exclusively known
from binary systems. In this work, we study gravitational microlensing of faint
background galaxies by isolated neutron stars (pulsars). We show that the
resulting surface brightness distortions can be used to determine the masses of
neutron star. Due to different evolutionary histories, isolated neutron stars
may have different masses from those in binary systems, and thus provide unique
insight into their equation of states under extreme physical conditions. We
search for existing pulsar catalogs and find one promising pair of a nearby
pulsar and a background galaxy. This method will become more practical for the
next generation optical and radio surveys and telescopes.Comment: 3 figures and 4 tables, accepted for publication in MNRA
Strings versus supersymmetric GUTs: can they be reconciled?
We describe a class of supersymmetric unified models with the following
properties:
i) the full breaking of the gauge group is achieved by Higgs fields in the
fundamental representation;
ii) the correct unification of the strong and electroweak coupling constants
is obtained without the need of any intermediate scale;
iii) the problems of the doublet-triplet splitting and of the proton decay at
dimension-5 level may receive a natural solution.
The models, other than being interesting unified field theories per se, may
constitute examples of string-derivable GUTs.Comment: 5 pages, report IFUP-TH 20/9
Extended Inflation from Strings
We study the possibility of extended inflation in the effective theory of
gravity from strings compactified to four dimensions and find that it strongly
depends on the mechanism of supersymmetry breaking. We consider a general class
of string--inspired models which are good candidates for successful extended
inflation. In particular, the --problem of ordinary extended inflation
is automatically solved by the production of only very small bubbles until the
end of inflation. We find that the inflaton field could belong either to the
untwisted or to the twisted massless sectors of the string spectrum, depending
on the supersymmetry breaking superpotential.Comment: 18p
Topological Inflation in Dual Superstring Models
We study the possibility of obtaining inflationary solutions from S-dual
superstring potentials. We find, in particular, that such solutions occur at
the core of domain walls separating degenerate minima whose positions differ by
modular transformations.Comment: 12 pages, uuencoded gzipped tar format, Latex, 2 figure
Fecal Enterobacteriales enrichment is associated with increased in vivo intestinal permeability in humans
Type 2 diabetes (T2D) has been linked with increased intestinal permeability, but the clinical significance of this phenomenon remains unknown. The objective of this study was to investigate the potential link between glucose control, intestinal permeability, diet and intestinal microbiota in patients with T2D. Thirtyâtwo males with wellâcontrolled T2D and 30 ageâmatched male controls without diabetes were enrolled in a caseâcontrol study. Metabolic parameters, inflammatory markers, endotoxemia, and intestinal microbiota in individuals subdivided into high (HP) and normal (LP) colonic permeability groups, were the main outcomes. In T2D, the HP group had significantly higher fasting glucose (P = 0.034) and plasma nonesterified fatty acid levels (P = 0.049) compared with the LP group. Increased colonic permeability was also linked with altered abundances of selected microbial taxa. The microbiota of both T2D and control HP groups was enriched with Enterobacteriales. In conclusion, high intestinal permeability was associated with poorer fasting glucose control in T2D patients and changes in some microbial taxa in both T2D patients and nondiabetic controls. Therefore, enrichment in the gramânegative order Enterobacteriales may characterize impaired colonic permeability prior to/independently from a disruption in glucose tolerance
Quantization from an exponential distribution of infinitesimal action
A statistical model of quantization based on an exponential distribution of
infinitesimal action is proposed. Trajectory which does not extremize the
action along an infinitesimal short segment of path is allowed to occur with a
very small probability following an exponential law. Planck constant is argued
to give the average deviation from the infinitesimal stationary action.Comment: 15 pages, accepted for publication in Physica
Unification of couplings and soft supersymmetry breaking terms in 4D superstring models
We consider the predictions for the hierarchy of mass scales, the fine
structure constant, the radii of compactification and the soft SUSY breaking
terms which follow if SUSY breaking is triggered by a gaugino condensate.Comment: 16 pages (LaTeX) Oxford preprint OUTP-93-32
- âŠ