15,779 research outputs found
The quantum inflaton, primordial perturbations and CMB fluctuations
We compute the primordial scalar, vector and tensor metric perturbations
arising from quantum field inflation. Quantum field inflation takes into
account the nonperturbative quantum dynamics of the inflaton consistently
coupled to the dynamics of the (classical) cosmological metric. For chaotic
inflation, the quantum treatment avoids the unnatural requirements of an
initial state with all the energy in the zero mode. For new inflation it allows
a consistent treatment of the explosive particle production due to spinodal
instabilities. Quantum field inflation (under conditions that are the quantum
analog of slow roll) leads, upon evolution, to the formation of a condensate
starting a regime of effective classical inflation. We compute the primordial
perturbations taking the dominant quantum effects into account. The results for
the scalar, vector and tensor primordial perturbations are expressed in terms
of the classical inflation results. For a N-component field in a O(N) symmetric
model, adiabatic fluctuations dominate while isocurvature or entropy
fluctuations are negligible. The results agree with the current WMAP
observations and predict corrections to the power spectrum in classical
inflation.Such corrections are estimated to be of the order of m^2/[N H^2]
where m is the inflaton mass and H the Hubble constant at horizon crossing.
This turns to be about 4% for the cosmologically relevant scales. This quantum
field treatment of inflation provides the foundations to the classical
inflation and permits to compute quantum corrections to it.Comment: 23 pages, no figures. Improved version to appear in Phys. Rev.
Tuning electronic structures via epitaxial strain in Sr2IrO4 thin films
We have synthesized epitaxial Sr2IrO4 thin-films on various substrates and
studied their electronic structures as a function of lattice-strains. Under
tensile (compressive) strains, increased (decreased) Ir-O-Ir bond-angles are
expected to result in increased (decreased) electronic bandwidths. However, we
have observed that the two optical absorption peaks near 0.5 eV and 1.0 eV are
shifted to higher (lower) energies under tensile (compressive) strains,
indicating that the electronic-correlation energy is also affected by in-plane
lattice-strains. The effective tuning of electronic structures under
lattice-modification provides an important insight into the physics driven by
the coexisting strong spin-orbit coupling and electronic correlation.Comment: 9 pages, 5 figures, 1 tabl
The bumpy light curve of supernova iPTF13z
A Type IIn supernova (SN) is dominated by the interaction of SN ejecta with
the circumstellar medium (CSM). Some SNe IIn (e.g., SN 2006jd) have episodes of
re-brightening ("bumps") in their light curves. We present iPTF13z, a SN IIn
discovered by the intermediate Palomar Transient Factory (iPTF) and
characterised by several bumps in its light curve. We analyse this peculiar
behaviour trying to infer the properties of the CSM and of the SN explosion, as
well as the nature of its progenitor star. We obtained multi-band optical
photometry for over 1000 days after discovery with the P48 and P60 telescopes
at Palomar Observatory. We obtained low-resolution optical spectra in the same
period. We did an archival search for progenitor outbursts. We analyse our
photometry and spectra, and compare iPTF13z to other SNe IIn. A simple
analytical model is used to estimate properties of the CSM. iPTF13z was a SN
IIn showing a light curve with five bumps during its decline phase. The bumps
had amplitudes between 0.4 and 0.9 mag and durations between 20 and 120 days.
The most prominent bumps appeared in all our different optical bands. The
spectra showed typical SN IIn characteristics, with emission lines of H
(with broad component FWHM ~ and narrow
component FWHM ~) and He I, but also with Fe II, Ca II,
Na I D and H P-Cygni profiles (with velocities of ~ ). A pre-explosion outburst was identified lasting days,
with mag around 210 days before discovery. Large, variable
progenitor mass-loss rates (~> 0.01 ) and CSM densities
(~> 10 g cm) are derived. We suggest that the light curve bumps
of iPTF13z arose from SN ejecta interacting with denser regions in the CSM,
possibly produced by the eruptions of a luminous blue variable star.Comment: Version 2: Update to match published paper. 21 pages, 14 figures,
abstract abridged to comply with arXiv length limit. In version 1 of the
paper on arXiv, Table 3 had some erroneous entries. Table 3 is now corrected
and available via VizieR. Version 1 comment: Accepted for publication in
Astronomy & Astrophysics (24 pages, 14 figures, abstract abridged by 20 % not
to exceed the arXiv length limit
On the possible space-time fractality of the emitting source
Using simple space-time implementation of the random cascade model we
investigate numerically a conjecture made some time ago which was joining the
intermittent behaviour of spectra of emitted particles with the possible
fractal structure of the emitting source. We demonstrate that such details are
seen, as expected, in the Bose-Einstein correlations between identical
particles. \\Comment: Thoroughly rewritten and modify version, to be published in Phys.
Rev.
QED Renormalization Given in A Mass-Dependent Subtraction and The Renormalization Group Approach
The QED renormalization is restudied by using a mass-dependent subtraction
which is performed at a time-like renormalization point. The subtraction
exactly respects necessary physical and mathematical requirements such as the
gauge symmetry, the Lorentz- invariance and the mathematical convergence.
Therefore, the renormalized results derived in the subtraction scheme are
faithful and have no ambiguity. Especially, it is proved that the solution of
the renormalization group equation satisfied by a renormalized wave function,
propagator or vertex can be fixed by applying the renormalization boundary
condition and, thus, an exact S-matrix element can be expressed in the form as
written in the tree diagram approximation provided that the coupling constant
and the fermion mass are replaced by their effective ones. In the one-loop
approximation, the effective coupling constant and the effective fermion mass
obtained by solving their renormalization group equations are given in rigorous
and explicit expressions which are suitable in the whole range of distance and
exhibit physically reasonable asymptotic behaviors.Comment: 29 pages, 4 figure
Wear and friction of Y-TZP spheres reciprocating against various Sialon plates
The friction and wear characteristics of various Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP)-Sialon sliding systems were examd. These systems consisted of a Y-TZP sphere reciprocating against various Sialon plates. The Sialons differed in phase content and compn. They range from a-Sialons to b-Sialons and include a-b composites. The length of the wear tracks was 10 mm, the loads used were 2 and 8 N, the frequencies 1, 4 and 8 Hz and the humidity was controlled by flushing with dry nitrogen. The tests were continued for 8, 24 and 72 h at room temp. The total vertical displacement and the friction coeff. were measured continuously and sampled. Various addnl. measurements were performed after each test and the worn surfaces were obsd. microscopically. It was concluded that the a-b composites show less wear than the single-phase a- and b-Sialons. It was also concluded that the amt. of wear increases approx. linearly with increasing load and increases significantly more than linearly with increasing frequency. A wear mechanism was derived incorporating the measured data and the observations. [on SciFinder (R)
Dense loops, supersymmetry, and Goldstone phases in two dimensions
Loop models in two dimensions can be related to O(N) models. The
low-temperature dense-loops phase of such a model, or of its reformulation
using a supergroup as symmetry, can have a Goldstone broken-symmetry phase for
N<2. We argue that this phase is generic for -2< N <2 when crossings of loops
are allowed, and distinct from the model of non-crossing dense loops first
studied by Nienhuis [Phys. Rev. Lett. 49, 1062 (1982)]. Our arguments are
supported by our numerical results, and by a lattice model solved exactly by
Martins et al. [Phys. Rev. Lett. 81, 504 (1998)].Comment: RevTeX, 5 pages, 3 postscript figure
Energy-momentum/Cotton tensor duality for AdS4 black holes
We consider the theory of gravitational quasi-normal modes for general linear
perturbations of AdS4 black holes. Special emphasis is placed on the effective
Schrodinger problems for axial and polar perturbations that realize
supersymmetric partner potential barriers on the half-line. Using the
holographic renormalization method, we compute the energy-momentum tensor for
perturbations satisfying arbitrary boundary conditions at spatial infinity and
discuss some aspects of the problem in the hydrodynamic representation. It is
also observed in this general framework that the energy-momentum tensor of
black hole perturbations and the energy momentum tensor of the gravitational
Chern-Simons action (known as Cotton tensor) exhibit an axial-polar duality
with respect to appropriately chosen supersymmetric partner boundary conditions
on the effective Schrodinger wave-functions. This correspondence applies to
perturbations of very large AdS4 black holes with shear viscosity to entropy
density ratio equal to 1/4\pi, thus providing a dual graviton description of
their hydrodynamic modes. We also entertain the idea that the purely
dissipative modes of black hole hydrodynamics may admit Ricci flow description
in the non-linear regime.Comment: 38 pages; minor typos corrected, a few extra references and a note
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