8,305 research outputs found
Accessing the topological susceptibility via the Gribov horizon
The topological susceptibility, , following the work of Witten and
Veneziano, plays a key role in identifying the relative magnitude of the
mass, the so-called problem. A nonzero is
caused by the Veneziano ghost, the occurrence of an unphysical massless pole in
the correlation function of the topological current. In a recent paper
(Phys.Rev.Lett.114 (2015) 24, 242001), an explicit relationship between this
Veneziano ghost and color confinement was proposed, by connecting the dynamics
of the Veneziano ghost, and thus the topological susceptibility, with Gribov
copies. However, the analysis is incompatible with BRST symmetry (Phys.Rev.D 93
(2016) no.8, 085010). In this paper, we investigate the topological
susceptibility, , in SU(3) and SU(2) Euclidean Yang-Mills theory using
an appropriate Pad\'e approximation tool and a non-perturbative gluon
propagator, within a BRST invariant framework and by taking into account Gribov
copies in a general linear covariant gauge.Comment: 17 pages, 4 figures. v2: corrected typos, new figures, improved style
of presentatio
Entanglement, Holography and Causal Diamonds
We argue that the degrees of freedom in a d-dimensional CFT can be
re-organized in an insightful way by studying observables on the moduli space
of causal diamonds (or equivalently, the space of pairs of timelike separated
points). This 2d-dimensional space naturally captures some of the fundamental
nonlocality and causal structure inherent in the entanglement of CFT states.
For any primary CFT operator, we construct an observable on this space, which
is defined by smearing the associated one-point function over causal diamonds.
Known examples of such quantities are the entanglement entropy of vacuum
excitations and its higher spin generalizations. We show that in holographic
CFTs, these observables are given by suitably defined integrals of dual bulk
fields over the corresponding Ryu-Takayanagi minimal surfaces. Furthermore, we
explain connections to the operator product expansion and the first law of
entanglement entropy from this unifying point of view. We demonstrate that for
small perturbations of the vacuum, our observables obey linear two-derivative
equations of motion on the space of causal diamonds. In two dimensions, the
latter is given by a product of two copies of a two-dimensional de Sitter
space. For a class of universal states, we show that the entanglement entropy
and its spin-three generalization obey nonlinear equations of motion with local
interactions on this moduli space, which can be identified with Liouville and
Toda equations, respectively. This suggests the possibility of extending the
definition of our new observables beyond the linear level more generally and in
such a way that they give rise to new dynamically interacting theories on the
moduli space of causal diamonds. Various challenges one has to face in order to
implement this idea are discussed.Comment: 84 pages, 12 figures; v2: expanded discussion on constraints in
section 7, matches published versio
Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates
In this study we investigate magnetic properties, surface morphology and
crystal structure in iron nanoclusters electrodeposited on lightly-doped (100)
n-type silicon substrates. Our goal is to investigate the spin injection and
detection in the Fe/Si lateral structures. The samples obtained under electric
percolation were characterized by magnetoresistive and magnetic resonance
measurements with cycling the sweeping applied field in order to understand the
spin dynamics in the as-produced samples. The observed hysteresis in the
magnetic resonance spectra, plus the presence of a broad peak in the
non-saturated regime confirming the low field microwave absorption (LFMA), were
correlated to the peaks and slopes found in the magnetoresistance curves. The
results suggest long range spin injection and detection in low resistive
silicon and the magnetic resonance technique is herein introduced as a
promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure
Thermodynamics of a charged relativistic ideal Boltzmann gas
This paper presents a toy model of a charged relativistic classical gas in
flat spacetime of an arbitrary number of dimensions equipped with some ``pair
production'' mechanism. Working with the microcanonical ensemble, the charge is
taken to be conserved in contrast with the total number of ``particles'' plus
``antiparticles'' which varies with temperature . Thermodynamics of the
classical gas is detailed studied in the nonrelativistic () as
well as in the ultrarelativistic () regimes. It is shown that,
although we are dealing with classical distributions, at the ultrarelativistic
regime the behavior of the gas is Planckian. We also compare the thermodynamics
of the toy model with that of quantum gases.Comment: 10 pages, no figures. Replaced by the published version in "Physica
A: Statistical Mechanics and its Applications
Clonal Composition of Human Adrenocortical Neoplasms
The mechanisms of tumorigenesis of adrenocortical neoplasms are still not understood. Tumor formation may be the result of spontaneous transformation of adrenocortical cells by somatic mutations. Another factor stimulating adrenocortical cell growth and potentially associated with formation of adrenal adenomas and, less frequently, carcinomas is the chronic elevation of proopiomelanocortin-derived peptides in diseases like ACTH-dependent Cushing's syndrome and congenital adrenal hyperplasia. To further investigate the pathogenesis of adrenocortical neoplasms, we studied the clonal composition of such tumors using X-chromosome inactivation analysis of the highly polymorphic region Xcen-Xp11.4 with the hybridization probe M27Ăź, which maps to a variable number of tandem repeats on the X-chromsome. In addition, polymerase chain reaction amplification of a phosphoglycerokinase gene polymorphism was performed. After DNA extraction from tumorous adrenal tissue and normal leukocytes in parallel, the active X-chromosome of each sample was digested with the methylation-sensitive restriction enzyme HpaII. A second digestion with an appropriate restriction enzyme revealed the polymorphism of the region Xcen-Xp11.4 and the phosphoglycerokinase locus. Whereas in normal polyclonal tissue both the paternal and maternal alleles are detected, a monoclonal tumor shows only one of the parental alleles. A total of 21 female patients with adrenal lesions were analyzed; 17 turned out to be heterozygous for at least one of the loci. Our results were as follows: diffuse (n = 4) and nodular (n = 1) adrenal hyperplasia in patients with ACTH-dependent Cushing's syndrome, polyclonal pattern; adrenocortical adenomas (n = 8), monoclonal (n = 7), as well as polyclonal (n = 1); adrenal carcinomas (n = 3), monoclonal pattern. One metastasis of an adrenocortical carcinoma showed a pattern most likely due to tumor-associated loss of methylation. In the special case of a patient with bilateral ACTH-independent macronodular hyperplasia, diffuse hyperplastic areas and a small nodule showed a polyclonal pattern, whereas a large nodule was monoclonal. We conclude that most adrenal adenomas and carcinomas are monoclonal, whereas diffuse and nodular adrenal hyperplasias are polyclonal. The clonal composition of ACTH-independent massive macronodular hyperplasia seems to be heterogeneous, consisting of polyclonal and monoclonal areas
Relaxation processes and entropic traps in the Backgammon model
We examine the density-density correlation function in a model recently
proposed to study the effect of entropy barriers in glassy dynamics. We find
that the relaxation proceeds in two steps with a fast beta process followed by
alpha relaxation. The results are physically interpreted in the context of an
adiabatic approximation which allows to separate the two processes, and to
define an effective temperature in the off-equilibrium dynamics of the model.
We investigate the behavior of the response function associated to the density,
and find violations of the fluctuation dissipation theorem.Comment: 4 Pages including 3 Figures, Revte
Transport properties of one-dimensional Kronig-Penney models with correlated disorder
Transport properties of one-dimensional Kronig-Penney models with binary
correlated disorder are analyzed using an approach based on classical
Hamiltonian maps. In this method, extended states correspond to bound
trajectories in the phase space of a parametrically excited linear oscillator,
while the on site-potential of the original model is transformed to an external
force. We show that in this representation the two probe conductance takes a
simple geometrical form in terms of evolution areas in phase-space. We also
analyze the case of a general N-mer model.Comment: 16 pages in Latex, 12 Postscript figures include
Poly(ADP-ribose)glycohydrolase is an upstream regulator of Ca2+ fluxes in oxidative cell death
Oxidative DNA damage to cells activates poly(ADP-ribose)polymerase-1 (PARP-1) and the poly(ADP-ribose) formed is rapidly degraded to ADP-ribose by poly(ADP-ribose)glycohydrolase (PARG). Here we show that PARP-1 and PARG control extracellular Ca2+ fluxes through melastatin-like transient receptor potential 2 channels (TRPM2) in a cell death signaling pathway. TRPM2 activation accounts for essentially the entire Ca2+ influx into the cytosol, activating caspases and causing the translocation of apoptosis inducing factor (AIF) from the inner mitochondrial membrane to the nucleus followed by cell death. Abrogation of PARP-1 or PARG function disrupts these signals and reduces cell death. ADP-ribose-loading of cells induces Ca2+ fluxes in the absence of oxidative damage, suggesting that ADP-ribose is the key metabolite of the PARP-1/PARG system regulating TRPM2. We conclude that PARP-1/PARG control a cell death signal pathway that operates between five different cell compartments and communicates via three types of chemical messengers: a nucleotide, a cation, and protein
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