10,749 research outputs found
Inflation in a two 3-form fields scenario
A setting constituted by 3-form fields, without any direct
interaction between them, minimally coupled to gravity, is introduced in this
paper as a framework to study the early evolution of the universe. We focus
particularly on the two 3-forms case. An inflationary scenario is found,
emerging from the coupling to gravity. More concretely, the fields coupled in
this manner exhibit a complex interaction, mediated by the time derivative of
the Hubble parameter. Our investigation is supported by means of a suitable
choice of potentials, employing numerical methods and analytical
approximations. In more detail, the oscillations on the small field limit
become correlated, and one field is intertwined with the other. In this type of
solution, a varying sound speed is present, together with the generation of
isocurvature perturbations. The mentioned features allow to consider an
interesting model, to test against observation. It is subsequently shown how
our results are consistent with current CMB data (viz.Planck and BICEP2).Comment: Version accepted in JCAP. 22 pages, 12 figures, new refs adde
Structure Effects on Coulomb Dissociation of B
Coulomb Dissociation provides an alternative method for determining the
radiative capture cross sections at astrophysically relevant low relative
energies. For the breakup of B on Ni, we calculate the total Coulomb
Dissociation cross section and the angular distribution for E1, E2 and M1. Our
calculations are performed first within the standard first order semiclassical
theory of Coulomb Excitation, including the correct three body kinematics, and
later including the projectile-target nuclear interactions.Comment: 6 pages, proceedings from International Workshop on RNB, Puri, India,
January 1998 - to be published in J. Phys.
The effects of multiple repairs on Inconel 718 weld mechanical properties
Inconel 718 weldments were repaired 3, 6, 9, and 13 times using the gas tungsten arc welding process. The welded panels were machined into mechanical test specimens, postweld heat treated, and nondestructively tested. Tensile properties and high cycle fatigue life were evaluated and the results compared to unrepaired weld properties. Mechanical property data were analyzed using the statistical methods of difference in means for tensile properties and difference in log means and Weibull analysis for high cycle fatigue properties. Statistical analysis performed on the data did not show a significant decrease in tensile or high cycle fatigue properties due to the repeated repairs. Some degradation was observed in all properties, however, it was minimal
On the particle spectrum and the conformal window
We study the SU(3) gauge theory with twelve flavours of fermions in the
fundamental representation as a prototype of non-Abelian gauge theories inside
the conformal window. Guided by the pattern of underlying symmetries, chiral
and conformal, we analyze the two-point functions theoretically and on the
lattice, and determine the finite size scaling and the infinite volume fermion
mass dependence of the would-be hadron masses. We show that the spectrum in the
Coulomb phase of the system can be described in the context of a universal
scaling analysis and we provide the nonperturbative determination of the
fermion mass anomalous dimension gamma*=0.235(46) at the infrared fixed point.
We comment on the agreement with the four-loop perturbative prediction for this
quantity and we provide a unified description of all existing lattice results
for the spectrum of this system, them being in the Coulomb phase or the
asymptotically free phase. Our results corroborate the view that the fixed
point we are studying is not associated to a physical singularity along the
bare coupling line and estimates of physical observables can be attempted on
either side of the fixed point. Finally, we observe the restoration of the U(1)
axial symmetry in the two-point functions.Comment: 40 pages, 22 figure
One,Two,Zero: Scales of Strong Interactions
We discuss our results on QCD with a number of fundamental fermions ranging
from zero to sixteen. These theories exhibit a wide array of fascinating
phenomena which have been under close scrutiny, especially in recent years,
first and foremost is the approach to conformality. To keep this review
focused, we have chosen scale generation, or lack thereof as a guiding theme,
however the discussion will be set in the general framework of the analysis of
the phases and phase transitions of strong interactions at zero and nonzero
temperature.Comment: 15 pages, prepared for IJMPA Special Issue 'Recent Nonperturbative
Developments in QCD-like Theories
Chiral symmetry restoration in QCD with many flavours
We discuss the phases of QCD in the parameter space spanned by the number of
light flavours and the temperature with respect to the realisation of chiral
and conformal symmetries. The intriguing interplay of these symmetries is best
studied by means of lattice simulations, and some selected results from our
recent work are presented here.Comment: 10 pages, proceedings of the 9th International Workshop on Critical
Point and Onset of Deconfinement, 17-21 November, 2014, ZiF, Bielefeld,
German
Peripherality of breakup reactions
The sensitivity of elastic breakup to the interior of the projectile wave
function is analyzed. Breakup calculations of loosely bound nuclei (8B and
11Be) are performed with two different descriptions of the projectile. The
descriptions differ strongly in the interior of the wave function, but exhibit
identical asymptotic properties, namely the same asymptotic normalization
coefficient, and phase shifts. Breakup calculations are performed at
intermediate energies (40-70 MeV/nucleon) on lead and carbon targets as well as
at low energy (26 MeV) on a nickel target. No dependence on the projectile
description is observed. This result confirms that breakup reactions are
peripheral in the sense that they probe only the external part of the wave
function. These measurements are thus not directly sensitive to the total
normalization of the wave function, i.e. spectroscopic factor.Comment: Reviewed version accepted for publication in Phys. Rev. C; 1 new
section (Sec. III E), 2 new figures (Figs. 3 and 5
Multi-alternative decision-making with non-stationary inputs
One of the most widely implemented models for multialternative
decision-making is the multihypothesis sequential
probability ratio test (MSPRT). It is asymptotically optimal,
straightforward to implement, and has found application in
modelling biological decision-making. However, the MSPRT
is limited in application to discrete (‘trial-based’), non-timevarying
scenarios. By contrast, real world situations will
be continuous and entail stimulus non-stationarity. In these
circumstances, decision-making mechanisms (like the MSPRT)
which work by accumulating evidence, must be able to discard
outdated evidence which becomes progressively irrelevant. To
address this issue, we introduce a new decision mechanism
by augmenting the MSPRT with a rectangular integration
window and a transparent decision boundary. This allows
selection and de-selection of options as their evidence changes
dynamically. Performance was enhanced by adapting the
window size to problem difficulty. Further, we present an
alternative windowing method which exponentially decays
evidence and does not significantly degrade performance,
while greatly reducing the memory resources necessary. The
methods presented have proven successful at allowing for the
MSPRT algorithm to function in a non-stationary environment
Nuclear reaction studies of unstable nuclei using relativistic mean field formalisms in conjunction with Glauber model
We study nuclear reaction cross-sections for stable and unstable projectiles
and targets within Glauber model, using densities obtained from various
relativistic mean field formalisms. The calculated cross-sections are compared
with the experimental data in some specific cases. We also evaluate the
differential scattering cross-sections at several incident energies, and
observe that the results found from various densities are similar at smaller
scattering angles, whereas a systematic deviation is noticed at large angles.
In general, these results agree fairly well with the experimental data.Comment: 9 pages, 7 figures, submitted to PR
Scaling Behavior of Driven Interfaces Above the Depinning Transition
We study the depinning transition for models representative of each of the
two universality classes of interface roughening with quenched disorder. For
one of the universality classes, the roughness exponent changes value at the
transition, while the dynamical exponent remains unchanged. We also find that
the prefactor of the width scales with the driving force. We propose several
scaling relations connecting the values of the exponents on both sides of the
transition, and discuss some experimental results in light of these findings.Comment: Revtex 3.0, 4 pages in PRL format + 5 figures (available at
ftp://jhilad.bu.edu/pub/abbhhss/ma-figures.tar.Z ) submitted to Phys Rev Let
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