30 research outputs found
A Gauge-Independent Mechanism for Confinement and Mass Gap: Part II -- G=SU(2) and D=3
We apply to the case of gauge group G = SU(2) in three dimensions a recently
proposed gauge-independent mechanism for confinement that is based on a
particular form of the dual spin foam framework for lattice gauge theory.
Explicit formulae for interaction factors and their asymptotics are introduced
and their behavior in different sectors of the theory are identified and
analyzed. We arrive at several elementary properties of the dual theory that
represent one scenario by which confinement may be realized at weak coupling.
We conclude with an outlook for further development of this approach.Comment: 18 pages, 3 figure
A Gauge-Independent Mechanism for Confinement and Mass Gap: Part I -- The General Framework
We propose a gauge-independent mechanism for the area-law behavior of Wilson
loop expectation values in terms of worldsheets spanning Wilson loops
interacting with the spin foams that contribute to the vacuum partition
function. The method uses an exact transformation of lattice-regularized
Yang-Mills theory that is valid for all couplings. Within this framework, some
natural conjectures can be made as to what physical mechanism enforces the
confinement property in the continuum (weak coupling) limit. Details for the
SU(2) case in three dimensions are provided in a companion paper.Comment: 16 pages, 4 figure
Positivity in Lorentzian Barrett-Crane Models of Quantum Gravity
The Barrett-Crane models of Lorentzian quantum gravity are a family of spin
foam models based on the Lorentz group. We show that for various choices of
edge and face amplitudes, including the Perez-Rovelli normalization, the
amplitude for every triangulated closed 4-manifold is a non-negative real
number. Roughly speaking, this means that if one sums over triangulations,
there is no interference between the different triangulations. We prove
non-negativity by transforming the model into a ``dual variables'' formulation
in which the amplitude for a given triangulation is expressed as an integral
over three copies of hyperbolic space for each tetrahedron. Then we prove that,
expressed in this way, the integrand is non-negative. In addition to implying
that the amplitude is non-negative, the non-negativity of the integrand is
highly significant from the point of view of numerical computations, as it
allows statistical methods such as the Metropolis algorithm to be used for
efficient computation of expectation values of observables.Comment: 13 page
Finiteness and Dual Variables for Lorentzian Spin Foam Models
We describe here some new results concerning the Lorentzian Barrett-Crane
model, a well-known spin foam formulation of quantum gravity. Generalizing an
existing finiteness result, we provide a concise proof of finiteness of the
partition function associated to all non-degenerate triangulations of
4-manifolds and for a class of degenerate triangulations not previously shown.
This is accomplished by a suitable re-factoring and re-ordering of integration,
through which a large set of variables can be eliminated. The resulting
formulation can be interpreted as a ``dual variables'' model that uses
hyperboloid variables associated to spin foam edges in place of representation
variables associated to faces. We outline how this method may also be useful
for numerical computations, which have so far proven to be very challenging for
Lorentzian spin foam models.Comment: 15 pages, 1 figur
Dual Computations of Non-abelian Yang-Mills on the Lattice
In the past several decades there have been a number of proposals for
computing with dual forms of non-abelian Yang-Mills theories on the lattice.
Motivated by the gauge-invariant, geometric picture offered by dual models and
successful applications of duality in the U(1) case, we revisit the question of
whether it is practical to perform numerical computation using non-abelian dual
models. Specifically, we consider three-dimensional SU(2) pure Yang-Mills as an
accessible yet non-trivial case in which the gauge group is non-abelian. Using
methods developed recently in the context of spin foam quantum gravity, we
derive an algorithm for efficiently computing the dual amplitude and describe
Metropolis moves for sampling the dual ensemble. We relate our algorithms to
prior work in non-abelian dual computations of Hari Dass and his collaborators,
addressing several problems that have been left open. We report results of spin
expectation value computations over a range of lattice sizes and couplings that
are in agreement with our conventional lattice computations. We conclude with
an outlook on further development of dual methods and their application to
problems of current interest.Comment: v1: 18 pages, 7 figures, v2: Many changes to appendix, minor changes
throughout, references and figures added, v3: minor corrections, 22 page
Histone deacetylases in viral infections
Chromatin remodeling and gene expression are regulated by histone deacetylases (HDACs) that condense the chromatin structure by deacetylating histones. HDACs comprise a group of enzymes that are responsible for the regulation of both cellular and viral genes at the transcriptional level. In mammals, a total of 18 HDACs have been identified and grouped into four classes, i.e., class I (HDACs 1, 2, 3, 8), class II (HDACs 4, 5, 6, 7, 9, 10), class III (Sirt1βSirt7), and class IV (HDAC11). We review here the role of HDACs on viral replication and how HDAC inhibitors could potentially be used as new therapeutic tools in several viral infections
Human Cytomegalovirus IE1 Protein Elicits a Type II Interferon-Like Host Cell Response That Depends on Activated STAT1 but Not Interferon-Ξ³
Human cytomegalovirus (hCMV) is a highly prevalent pathogen that, upon primary
infection, establishes life-long persistence in all infected individuals. Acute
hCMV infections cause a variety of diseases in humans with developmental or
acquired immune deficits. In addition, persistent hCMV infection may contribute
to various chronic disease conditions even in immunologically normal people. The
pathogenesis of hCMV disease has been frequently linked to inflammatory host
immune responses triggered by virus-infected cells. Moreover, hCMV infection
activates numerous host genes many of which encode pro-inflammatory proteins.
However, little is known about the relative contributions of individual viral
gene products to these changes in cellular transcription. We systematically
analyzed the effects of the hCMV 72-kDa immediate-early 1 (IE1) protein, a major
transcriptional activator and antagonist of type I interferon (IFN) signaling,
on the human transcriptome. Following expression under conditions closely
mimicking the situation during productive infection, IE1 elicits a global type
II IFN-like host cell response. This response is dominated by the selective
up-regulation of immune stimulatory genes normally controlled by IFN-Ξ³ and
includes the synthesis and secretion of pro-inflammatory chemokines.
IE1-mediated induction of IFN-stimulated genes strictly depends on
tyrosine-phosphorylated signal transducer and activator of transcription 1
(STAT1) and correlates with the nuclear accumulation and sequence-specific
binding of STAT1 to IFN-Ξ³-responsive promoters. However, neither synthesis
nor secretion of IFN-Ξ³ or other IFNs seems to be required for the
IE1-dependent effects on cellular gene expression. Our results demonstrate that
a single hCMV protein can trigger a pro-inflammatory host transcriptional
response via an unexpected STAT1-dependent but IFN-independent mechanism and
identify IE1 as a candidate determinant of hCMV pathogenicity