500 research outputs found
Transport coefficients, spectral functions and the lattice
Transport coefficients are determined by the slope of spectral functions of
composite operators at zero frequency. We study the spectral function relevant
for the shear viscosity for arbitrary frequencies in weakly-coupled scalar and
nonabelian gauge theories at high temperature and compute the corresponding
correlator in euclidean time. We discuss whether nonperturbative values of
transport coefficients can be extracted from euclidean lattice simulations.Comment: 25 pages with 7 eps figures, discussion improved, acknowledgement
added; to appear in JHE
Phantom Field with O(N) Symmetry in Exponential Potential
In this paper, we study the phase space of phantom model with O(\emph{N})
symmetry in exponential potential. Different from the model without O(\emph{N})
symmetry, the introduction of the symmetry leads to a lower bound on the
equation of state for the existence of stable phantom dominated attractor
phase. The reconstruction relation between the potential of O(\textit{N})
phantom system and red shift has been derived.Comment: 5 pages, 3 figures, replaced with the version to appear on Phys. Rev.
Transition from decelerated to accelerated cosmic expansion in braneworld universes
Braneworld theory provides a natural setting to treat, at a classical level,
the cosmological effects of vacuum energy. Non-static extra dimensions can
generally lead to a variable vacuum energy, which in turn may explain the
present accelerated cosmic expansion. We concentrate our attention in models
where the vacuum energy decreases as an inverse power law of the scale factor.
These models agree with the observed accelerating universe, while fitting
simultaneously the observational data for the density and deceleration
parameter. The redshift at which the vacuum energy can start to dominate
depends on the mass density of ordinary matter. For Omega = 0.3, the transition
from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/-
0.20, which is compatible with SNe data. We set a lower bound on the
deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for
Omega = 0.3. The future evolution of the universe crucially depends on the time
when vacuum starts to dominate over ordinary matter. If it dominates only
recently, at an epoch z < 0.64, then the universe is accelerating today and
will continue that way forever. If vacuum dominates earlier, at z > 0.64, then
the deceleration comes back and the universe recollapses at some point in the
distant future. In the first case, quintessence and Cardassian expansion can be
formally interpreted as the low energy limit of our model, although they are
entirely different in philosophy. In the second case there is no correspondence
between these models and ours.Comment: In V2 typos are corrected and one reference is added for section 1.
To appear in General Relativity and Gravitatio
Eradication of large solid tumors by gene therapy with a T cell receptor targeting a single cancer-specific point mutation
PURPOSE: Cancers usually contain multiple unique tumor-specific antigens produced by single amino acid substitutions (AAS) and encoded by somatic non-synonymous single nucleotide substitutions. We determined whether adoptively transferred T cells can reject large, well-established solid tumors when engineered to express a single type of T cell receptor (TCR) that is specific for a single AAS. EXPERIMENTAL DESIGN: By exome and RNA sequencing of an UV-induced tumor, we identified an AAS in p68 (mp68), a co-activator of p53. This AAS seemed to be an ideal tumor-specific neoepitope because it is encoded by a trunk mutation in the primary autochthonous cancer and binds with highest affinity to the MHC. A high-avidity mp68-specific TCR was used to genetically engineer T cells as well as to generate TCR-transgenic mice for adoptive therapy. RESULTS: When the neoepitope was expressed at high levels and by all cancer cells, their direct recognition sufficed to destroy intra-tumor vessels and eradicate large, long-established solid tumors. When the neoepitope was targeted as autochthonous antigen, T cells caused cancer regression followed by escape of antigen-negative variants. Escape could be thwarted by expressing the antigen at increased levels in all cancer cells or by combining T cell therapy with local irradiation. Therapeutic efficacies of TCR-transduced and TCR-transgenic T cells were similar. CONCLUSIONS: Gene therapy with a single TCR targeting a single AAS can eradicate large established cancer but a uniform expression and/or sufficient levels of the targeted neoepitope or additional therapy are required to overcome tumor escape
Accelerated expansion from braneworld models with variable vacuum energy
In braneworld models a variable vacuum energy may appear if the size of the
extra dimension changes during the evolution of the universe. In this scenario
the acceleration of the universe is related not only to the variation of the
cosmological term, but also to the time evolution of and, possibly, to the
variation of other fundamental "constants" as well. This is because the
expansion rate of the extra dimension appears in different contexts, notably in
expressions concerning the variation of rest mass and electric charge. We
concentrate our attention on spatially-flat, homogeneous and isotropic,
brane-universes where the matter density decreases as an inverse power of the
scale factor, similar (but at different rate) to the power law in FRW-universes
of general relativity.
We show that these braneworld cosmologies are consistent with the observed
accelerating universe and other observational requirements. In particular,
becomes constant and asymptotically in
time. Another important feature is that the models contain no "adjustable"
parameters. All the quantities, even the five-dimensional ones, can be
evaluated by means of measurements in 4D. We provide precise constrains on the
cosmological parameters and demonstrate that the "effective" equation of state
of the universe can, in principle, be determined by measurements of the
deceleration parameter alone. We give an explicit expression relating the
density parameters , and the deceleration
parameter . These results constitute concrete predictions that may help in
observations for an experimental/observational test of the model.Comment: References added, typos correcte
Multiple CDM cosmology with string landscape features and future singularities
Multiple CDM cosmology is studied in a way that is formally a
classical analog of the Casimir effect. Such cosmology corresponds to a
time-dependent dark fluid model or, alternatively, to its scalar field
presentation, and it motivated by the string landscape picture. The future
evolution of the several dark energy models constructed within the scheme is
carefully investigated. It turns out to be almost always possible to choose the
parameters in the models so that they match the most recent and accurate
astronomical values. To this end, several universes are presented which mimick
(multiple) CDM cosmology but exhibit Little Rip, asymptotically de
Sitter, or Type I, II, III, and IV finite-time singularity behavior in the far
future, with disintegration of all bound objects in the cases of Big Rip,
Little Rip and Pseudo-Rip cosmologies.Comment: LaTeX 11 pages, 10 figure
Parameterization and Reconstruction of Quasi Static Universe
We study a possibility of the fate of universe, in which there is neither the
rip singularity, which results in the disintegration of bound systems, nor the
endless expansion, instead the universe will be quasi static. We discuss the
parameterization of the corresponding evolution and the reconstruction of the
scalar field model. We find, with the parameterization consistent with the
current observation, that the current universe might arrive at a quasi static
phase after less than 20Gyr.Comment: minor changes and Refs. added, publish in EPJ
Measurement of (1020) meson leptonic width with CMD-2 detector at VEPP-2M Collider
The (1020) meson leptonic width has been determined from the combined
analysis of 4 major decay modes of the resonance () studied with the CMD-2 detector at
the VEPP-2M collider. The following value has been obtained:
keV.
The meson parameters in four main decay channels have been also
recalculated: , , , .Comment: 14 pages, 3 figure
Operation of universal gates in a DXD superconducting solid state quantum computer
We demonstrate that complete set of gates can be realized in a DXD
superconducting solid state quantum computer (quamputer), thereby proving its
universality.Comment: 4 pages, 2 figure
Planck-scale quintessence and the physics of structure formation
In a recent paper we considered the possibility of a scalar field providing
an explanation for the cosmic acceleration. Our model had the interesting
properties of attractor-like behavior and having its parameters of O(1) in
Planck units. Here we discuss the effect of the field on large scale structure
and CMB anisotropies. We show how some versions of our model inspired by
"brane" physics have novel features due to the fact that the scalar field has a
significant role over a wider range of redshifts than for typical "dark energy"
models. One of these features is the additional suppression of the formation of
large scale structure, as compared with cosmological constant models. In light
of the new pressures being placed on cosmological parameters (in particular
H_0) by CMB data, this added suppression allows our "brane" models to give
excellent fits to both CMB and large scale structure data.Comment: 18 pages, 12 figures, submitted to PR
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