1,941 research outputs found
Nucleon-Nucleon Scattering in a Strong External Magnetic Field and the Neutrino Emissivity
The nucleon-nucleon scattering in a large magnetic background is considered
to find its potential to change the neutrino emissivity of the neutron stars.
For this purpose we consider the one-pion-exchange approximation to find the NN
cross-section in a background field as large as
. We show that the NN cross-section in
neutron stars with temperatures in the range 0.1-5 \texttt{MeV} can be changed
up to the one order of magnitude with respect to the one in the absence of the
magnetic field. In the limit of the soft neutrino emission the neutrino
emissivity can be written in terms of the NN scattering amplitude therefore the
large magnetic fields can dramatically change the neutrino emissivity of the
neutron stars as well.Comment: 21 pages, 5 figures, to appear in PR
Multiphysics discovery with moving boundaries using Ensemble SINDy and Peridynamic Differential Operator
This study proposes a novel framework for learning the underlying physics of
phenomena with moving boundaries. The proposed approach combines Ensemble SINDy
and Peridynamic Differential Operator (PDDO) and imposes an inductive bias
assuming the moving boundary physics evolve in its own corotational coordinate
system. The robustness of the approach is demonstrated by considering various
levels of noise in the measured data using the 2D Fisher-Stefan model. The
confidence intervals of recovered coefficients are listed, and the
uncertainties of the moving boundary positions are depicted by obtaining the
solutions with the recovered coefficients. Although the main focus of this
study is the Fisher-Stefan model, the proposed approach is applicable to any
type of moving boundary problem with a smooth moving boundary front without a
mushy region. The code and data for this framework is available at:
https://github.com/alicanbekar/MB_PDDO-SINDy.Comment: 26 pages, 22 figures, submitted to Proceedings of the Royal Society
Positronium Hyperfine Splitting in Non-commutative Space at the Order
We obtain positronium Hyperfine Splitting owing to the non-commutativity of
space and show that, in the leading order, it is proportional to where, is the parameter of non-commutativity. It is also
shown that spatial non-commutativity splits the spacing between triplet
excited levels which provides an experimental test on
the non-commutativity of space.Comment: 7 pages, 2 figures, to appear in Phys. Rev.
Generation of circular polarization of the CMB
According to the standard cosmology, near the last scattering surface, the
photons scattered via Compton scattering are just linearly polarized and then
the primordial circular polarization of the CMB photons is zero. In this work
we show that CMB polarization acquires a small degree of circular polarization
when a background magnetic field is considered or the quantum electrodynamic
sector of standard model is extended by Lorentz-noninvariant operators as well
as noncommutativity. The existence of circular polarization for the CMB
radiation may be verified during future observation programs and it represents
a possible new channel for investigating new physics effects.Comment: 28 pages, v3, Phys. Rev. D 81, 084035 (2010
The effect of loading rate on fracture energy of asphalt mixture at intermediate temperatures and under different loading modes
At intermediate service temperatures hot mix asphalt (HMA) concretely are subjected to different loading rates due to movement of vehicles which can significantly affect their mechanical characteristics and final service load. Hence, in this paper the effect of loading rate on intermediate temperature fracture resistance of HMA materials is investigated experimentally in different modes of cracking. Different hot mix asphalt mixtures made of various compositions were subjected to asymmetric threepoint bend loading in the form of edge cracked semi-circular bend (SCB) specimens. The effect of aggregate type and air void were studied on the fracture energy values for three mode mixities (including pure mode I, mixed mode I/II and pure mode II) and at different temperatures of 5°C, 15°C and 25°C. Trends of change in fracture energy values revealed noticeable influence of loading rate on the low and intermediate temperature cracking behavior of tested asphalt mixtures with different air void contents and aggregate types subjected to mixed mode I/II loading. Also, a change observed in fracture resistance of asphalt mixtures at nearly zero (5°C) and intermediate temperatures (25°C) that was due to change in the behavior of bitumen from elastic to viscoelastic. © 2018, Gruppo Italiano Frattura. All rights reserved
Neutrino-electron scattering in noncommutative space
Neutral particles can couple with the gauge field in the adjoint
representation at the tree level if the space-time coordinates are
noncommutative (NC). Considering neutrino-photon coupling in the NC QED
framework, we obtain the differential cross section of neutrino-electron
scattering. Similar to the magnetic moment effect, one of the NC terms is
proportional to , where is the electron recoil energy.
Therefore, this scattering provides a chance to achieve a stringent bound on
the NC scale in low energy by improving the sensitivity to the smaller electron
recoil energy.Comment: 12 pages, 2 figure
Constraining noncommutative field theories with holography
An important window to quantum gravity phenomena in low energy noncommutative
(NC) quantum field theories (QFTs) gets represented by a specific form of UV/IR
mixing. Yet another important window to quantum gravity, a holography,
manifests itself in effective QFTs as a distinct UV/IR connection. In matching
these two principles, a useful relationship connecting the UV cutoff
, the IR cutoff and the scale of
noncommutativity , can be obtained. We show that an effective
QFT endowed with both principles may not be capable to fit disparate
experimental bounds simultaneously, like the muon and the masslessness of
the photon. Also, the constraints from the muon preclude any possibility
to observe the birefringence of the vacuum coming from objects at cosmological
distances. On the other hand, in NC theories without the UV completion, where
the perturbative aspect of the theory (obtained by truncating a power series in
) becomes important, a heuristic estimate of the region
where the perturbative expansion is well-defined , gets affected when holography is applied by providing the energy of the
system a -dependent lower limit. This may affect models
which try to infer the scale by using data from low-energy
experiments.Comment: 4 pages, version to be published in JHE
Three Body Bound State in Non-Commutative Space
The Bethe-Salpeter equation in non-commutative QED (NCQED) is considered for
three-body bound state. We study the non-relativistic limit of this equation in
the instantaneous approximation and derive the corresponding Schr\"{o}dinger
equation in non-commutative space. It is shown that the experimental data for
Helium atom puts an upper bound on the magnitude of the parameter of
non-commutativity, .Comment: 10 pages, 3 figures, to appear in Phys. Rev.
Direct Integration and Non-Perturbative Effects in Matrix Models
We show how direct integration can be used to solve the closed amplitudes of
multi-cut matrix models with polynomial potentials. In the case of the cubic
matrix model, we give explicit expressions for the ring of non-holomorphic
modular objects that are needed to express all closed matrix model amplitudes.
This allows us to integrate the holomorphic anomaly equation up to holomorphic
modular terms that we fix by the gap condition up to genus four. There is an
one-dimensional submanifold of the moduli space in which the spectral curve
becomes the Seiberg--Witten curve and the ring reduces to the non-holomorphic
modular ring of the group . On that submanifold, the gap conditions
completely fix the holomorphic ambiguity and the model can be solved explicitly
to very high genus. We use these results to make precision tests of the
connection between the large order behavior of the 1/N expansion and
non-perturbative effects due to instantons. Finally, we argue that a full
understanding of the large genus asymptotics in the multi-cut case requires a
new class of non-perturbative sectors in the matrix model.Comment: 51 pages, 8 figure
Solving the Topological String on K3 Fibrations
We present solutions of the holomorphic anomaly equations for compact
two-parameter Calabi-Yau manifolds which are hypersurfaces in weighted
projective space. In particular we focus on K3-fibrations where due to
heterotic type II duality the topological invariants in the fibre direction are
encoded in certain modular forms. The formalism employed provides holomorphic
expansions of topological string amplitudes everywhere in moduli space.Comment: 60 pages, 1 figure, With an appendix by Sheldon Kat
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