623 research outputs found
D-Branes and Topological Field Theories
In the presence of a D-brane a string theory develops a new subsector. We
show that for curved D-branes the corresponding sector is a (partially twisted)
topological field theory. We use this result to compute the degeneracy of
2-branes wrapped around cycles as well as 3-branes wrapped around CY
threefold vanishing 3-cycles. In both cases we find the degeneracy is in accord
with expectation. The counting of BPS states of a gas of 0-branes in the
presence of a 4-brane in is considered and it is noted that the effective
0-brane charge is shifted by 1, due to a quantum correction. This is in accord
with string duality and the fact that left-moving ground state energy of
heterotic string starts at . We also show that all the three different
topological twistings of four dimensional Yang-Mills theory do arise from
curved three-branes embedded in different spaces (Calabi-Yau manifolds and
manifolds with exceptional holonomy groups).Comment: 22 page
Nutritional intervention and impact of polyphenol on glycohaemoglobin (HbA1c) in non-diabetic and type 2 diabetic subjects: systematic review and meta-analysis
Polyphenols have been extensively studied for their antioxidant and anti-inflammatory properties. Recently, their antiglycative actions by oxidative stress modulation have been linked to prevention of diabetes and associated complications. This paper assesses the evidence for polyphenol interventions on glycohaemoglobin (HbA1c) in non-diabetic, pre-diabetic and type 2 diabetes mellitus (T2DM) subjects. A systematic review of polyphenols clinical trials on HbA1c in humans was performed according to the Preferred Reporting Items for Systematic Review and Meta-Analysis. Thirty-six controlled randomized trials with HbA1c values were included. Polyphenols (extracts, supplements, foods), were supplemented (28 mg to 1.5g) for 0.7 to 12 months. Combining all subjects (n=1954, mean baseline HbA1c=7.03%, 53 mmol/mol), polyphenol supplementation significantly (p<0.001) lowered HbA1c% by -0.53±0.12 units (-5.79±0.13 mmol/mol). This reduction was significant (p<0.001) in T2DM subjects, specifically (n=1426, mean baseline HbA1c=7.44%, 58 mmol/mol), with HbA1c% lowered by -0.21±0.04 units (-2.29±0.4 mmol/mol). Polyphenol supplementation had no significant effect (p>0.21) in the non-diabetic (n=258, mean baseline HbA1c=5.47%, 36 mmol/mol) and the pre-diabetic subjects (n=270, mean baseline HbA1c=6.06%, 43 mmol/mol) strata: -0.39±0.27 HbA1c% units (-4.3±0.3 mmol/mol), and -0.38±0.31 units (-4.2±0.31 mmol/mol), respectively. In conclusion, polyphenols can successfully reduce HbA1c in T2DM, without any intervention at glycaemia, and could contribute to the prevention of diabetes complications
D-Strings on D-Manifolds
We study the mechanism for appearance of massless solitons in type II string
compactifications. We find that by combining -duality with strong/weak
duality of type IIB in 10 dimensions enhanced gauge symmetries and massless
solitonic hypermultiplets encountered in Calabi-Yau compactifications can be
studied perturbatively using D-strings (the strong/weak dual to type IIB
string) compactified on ``D-manifolds''. In particular the nearly massless
solitonic states of the type IIB compactifications correspond to elementary
states of D-strings. As examples we consider the D-string description of
enhanced gauge symmetries for type IIA string compactification on ALE spaces
with singularities and type IIB on a class of singular Calabi-Yau
threefolds. The class we study includes as a special case the conifold
singularity in which case the perturbative spectrum of the D-string includes
the expected massless hypermultiplet with degeneracy one.Comment: 23 pages, with 3 figures. A compact example is adde
Spontaneous Parity Violation in QCD At Finite Temperature: On the Inapplicability of the Vafa-Witten Theorem
The generalization of the Vafa-Witten theorem ruling out parity violation to
QCD at finite temperature is considered. It is shown that this generalization
of the theorem rules out Lorentz-invariant parity violating operators from
spontaneously acquiring vacuum expectation values. However, it does not rule
out Lorentz-noninvariant parity-violating operators from acquiring expectation
values. Other situations where the theorem is inapplicable are also discussed.Comment: Minor typos correcte
Superpotentials from flux compactifications of M-theory
In flux compactifications of M-theory a superpotential is generated whose
explicit form depends on the structure group of the 7-dimensional internal
manifold. In this note, we discuss superpotentials for the structure groups:
G_2, SU(3) or SU(2). For the G_2 case all internal fluxes have to vanish. For
SU(3) structures, the non-zero flux components entering the superpotential
describe an effective 1-dimensional model and a Chern-Simons model if there are
SU(2) structures.Comment: 10 page
A-Model Correlators from the Coulomb Branch
We compute the contribution of discrete Coulomb vacua to A-Model correlators
in toric Gauged Linear Sigma Models. For models corresponding to a compact
variety, this determines the correlators at arbitrary genus. For non-compact
examples, our results imply the surprising conclusion that the quantum
cohomology relations break down for a subset of the correlators.Comment: 27 pages, 1 xy-pic figur
Producing a Scale-Invariant Spectrum of Perturbations in a Hagedorn Phase of String Cosmology
We study the generation of cosmological perturbations during the Hagedorn
phase of string gas cosmology. Using tools of string thermodynamics we provide
indications that it may be possible to obtain a nearly scale-invariant spectrum
of cosmological fluctuations on scales which are of cosmological interest
today. In our cosmological scenario, the early Hagedorn phase of string gas
cosmology goes over smoothly into the radiation-dominated phase of standard
cosmology, without having a period of cosmological inflation.Comment: 4 pages, 1 figur
F-theory, Geometric Engineering and N=1 Dualities
We consider geometric engineering of N=1 supersymmetric QFTs with matter in
terms of a local model for compactification of F-theory on Calabi-Yau fourfold.
By bringing 3-branes near 7-branes we engineer N=1 supersymmetric
gauge theory with flavors in the fundamental. We identify the Higgs
branch of this system with the instanton moduli space on the compact four
dimensional space of the 7-brane worldvolume. Moreover we show that the
Euclidean 3-branes wrapped around the compact part of the 7-brane worldvolume
can generate superpotential for as well as lead to quantum
corrections to the moduli space for . Finally we argue that Seiberg's
duality for N=1 supersymmetric QCD may be mapped to T-duality exchanging
7-branes with 3-branes.Comment: 15 page
Topological Reduction of 4D SYM to 2D --Models
By considering a (partial) topological twisting of supersymmetric Yang-Mills
compactified on a 2d space with `t Hooft magnetic flux turned on we obtain a
supersymmetric -model in 2 dimensions. For N=2 SYM this maps Donaldson
observables on products of two Riemann surfaces to quantum cohomology ring of
moduli space of flat connections on a Riemann surface. For N=4 SYM it maps
-duality to -duality for -models on moduli space of solutions to
Hitchin equations.Comment: 30 pages, harvma
Superstrings with new supersymmetry in (9,2) and (10,2) dimensions
We construct superstring theories that obey the new supersymmetry algebra
{Q_a , Q_b}=\gamma_{ab}^{mn} P_{1m} P_{2n}, in a Green-Schwarz formalism, with
kappa supersymmetry also of the new type. The superstring is in a system with a
superparticle so that their total momenta are respectively. The
system is covariant and critical in (10,2) dimensions if the particle is
massless and in (9,2) dimensions if the particle is massive. Both the
superstring and superparticle have coordinates with two timelike dimensions but
each behaves effectively as if they have a single timelike dimension. This is
due to gauge symmetries and associated constraints. We show how to generalize
the gauge principle to more intricate systems containing two parts, 1 and 2.
Each part contains interacting constituents, such as p-branes, and each part
behaves effectively as if they have one timelike coordinate, although the full
system has two timelike coordinates. The examples of two superparticles, and of
a superparticle and a superstring, discussed in more detail are a special cases
of such a generalized interacting system.Comment: LaTeX, revtex, 9 page
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