15,369 research outputs found
Phase ambiguity of the threshold amplitude in pp -> pp\pi^0
Measurements of spin observables in pp -> {\vec p}{\vec p}\pi^0 are suggested
to remove the phase ambiguity of the threshold amplitude. The suggested
measurements complement the IUCF data on {\vec p}{\vec p} -> pp\pi^0 to
completely determine all the twelve partial wave amplitudes, taken into
consideration by Mayer et.al. [15] and Deepak, Haidenbauer and Hanhart [20].Comment: 4 pages, 1 table
Nebular Spectra and Explosion Asymmetry of Type Ia Supernovae
The spectral signatures of asymmetry in Type Ia Supernova (SN Ia) explosions
are investigated, using a sample of late-time nebular spectra. First, a
kinematical model is constructed for SN Ia 2003hv, which can account for the
main features in its optical, Near-Infrared (NIR), and Mid-Infrared (Mid-IR)
late-time spectra. It is found that an asymmetric off-center model can explain
the observed characteristics of SN 2003hv. This model includes a relatively
high density, Fe-rich region which displays a large velocity off-set, and a
relatively low density, extended 56Ni-rich region which is more spherically
distributed. The high density region consists of the inner stable Fe-Ni region
and outer 56Ni-rich region. Such a distribution may be the result of a
delayed-detonation explosion, in which the first deflagration produces the
global asymmetry in the innermost ejecta, while the subsequent detonation can
lead to the bulk spherical symmetry. This configuration, if viewed from the
direction of the off-set, can consistently explain the blueshift in some of the
emission lines and virtually no observed shift in other lines in SN 2003hv. For
this model, we then explore the effects of different viewing angles and the
implications for SNe Ia in general. The model predicts that a variation of the
central wavelength, depending on the viewing angle, should be seen in some
lines (e.g., [Ni II]7378), while the strongest lines (e.g., [Fe III] blend at
4700A) will not show this effect. By examining optical nebular spectra of 12
SNe Ia, we have found that such a variation indeed exists. We suggest that the
global asymmetry in the innermost ejecta, as likely imprint of the deflagration
flame propagation, is a generic feature of SNe Ia (abridged).Comment: 14 pages, 11 figures, 4 tables. Accepted for publication in the
Astrophysical Journal. Minor correction
Inflation from Superstring/M-Theory Compactification with Higher Order Corrections II -- Case of Quartic Weyl Terms --
We present a detailed study of inflationary solutions in M-theory with higher
order quantum corrections. We first exhaust all exact and asymptotic solutions
of exponential and power-law expansions in this theory with quartic curvature
corrections, and then perform a linear perturbation analysis around fixed
points for the exact solutions in order to see which solutions are more generic
and give interesting cosmological models. We find an interesting solution in
which the external space expands exponentially and the internal space is static
both in the original and Einstein frames. This may be regarded as moduli
stabilization by higher order corrections. Furthermore, we perform a numerical
calculation around this solution and find numerical solutions which give enough
e-foldings. We also briefly summarize similar solutions in type II
superstrings.Comment: 40 pages, 11 figures, v2: additional explanations, refs. added, to
appear in PR
Meissner effect in the layered Kane-Mele model with Hubbard interaction
We investigate the magnetic response in the quantum spin Hall phase of the
layered Kane-Mele model with Hubbard interaction, and argue a condition to
obtain the Meissner effect. The effect of Rashba spin orbit coupling is also
discussed.Comment: 4 pages, accepted for publication in Journal of Physics: Conference
Series as proceedings of International Symposium "Nanoscience and Quantum
Physics 2011" (nanoPHYS'11) held in Toky
Radiation from an accelerated quark via AdS/CFT
In this paper we investigate radiation by an accelerated quark in a strongly
coupled gauge theory via AdS/CFT correspondence. According to AdS/CFT
dictionary, we can read off energy density or energy flux of the radiation from
asymptotic gravitational field in AdS bulk sourced by an accelerated string
trailing behind the quark. In the case of an oscillating quark with frequency
, we show that the time averaged energy density is asymptotically
isotropic and it falls off as with
distance from the source. In a toy model of a scattered quark by an
external field, we simply estimate Poynting vector by the bremsstrahlung
radiation and show that the energy flux is anisotropic outgoing radiation.
Based on these investigations, we discuss the properties of strongly coupled
gauge theory radiation in comparison with electromagnetic radiation.Comment: 16 pages, no figures, accepted for publication in Phys. Rev.
A study of gamma ray bursts with afterglow plateau phases associated with supernovae
The analysis of 176 gamma ray burst (GRB) afterglow plateaus observed by
Swift from GRBs with known redshifts revealed that the subsample of long GRBs
associated with supernovae (LONG-SNe) - 19 events - presents a very high
correlation coefficient between the luminosity at the end of the plateau phase
La and the end time of the plateau T*a, hereafter Dainotti relation.
Furthermore, these SNe Ib/c associated with GRBs also obey the peak-magnitude
stretch relation, similar to that used to standardize the SNe Ia. We here
investigate a category of GRBs with plateau and associated with SNe to compare
the Dainotti correlation for this sample with the correlation for long GRBs for
which no associated SN has been observed (hereafter LONG-NO-SNe, 128 GRBs) and
to check whether there is a difference among these sub-samples. We first
adopted a non-parametric statistical method to take redshift evolution into
account and to check if and how this effect may steepen the slope for the
LONG-NO-SNe sample. Therefore, removing selection bias is the first step before
any comparison among samples observed at different redshifts could be properly
performed. Then, we applied the T-student test to evaluate a statistical
difference between the slopes of the two samples. We demonstrate that there is
no evolution for the slope of the LONG-NO-SNe sample and no evolution is
expected for the LONG-SNe sample at small redshifts. The difference between the
slope of the LONG-NO-SNe and the slope of LONG-SNe with firm spectral detection
of SN components, is statistically significant. This possibly suggests that,
unlike LONG-NO-SNe, LONG-SNe with firm spectroscopic features of the associated
SNe might not require a standard energy reservoir in the plateau phase.
Therefore, this analysis may open new perspectives in future theoretical
investigations of the GRBs with plateau emission and that are associated with
SNe.Comment: 11 pages, 10 figures, 2 Tables, in press on Astronomy and
Astrophysics, 8 dicember 201
Creation of the universe with a stealth scalar field
The stealth scalar field is a non-trivial configuration without any
back-reaction to geometry, which is characteristic for non-minimally coupled
scalar fields. Studying the creation probability of the de Sitter universe with
a stealth scalar field by the Hartle and Hawking's semi-classical method, we
show that the effect of the stealth field can be significant. For the class of
scalar fields we consider, creation with a stealth field is possible for a
discrete value of the coupling constant and its creation probability is always
less than that with a trivial scalar field. However, those creation rates can
be almost the same depending on the parameters of the theory.Comment: 7 pages; v2, references added; v3, creation of the open universe
adde
The Progenitor of the Type IIb SN 2008ax Revisited
Hubble Space Telescope observations of the site of the supernova (SN) 2008ax
obtained in 2011 and 2013 reveal that the possible progenitor object detected
in pre-explosion images was in fact multiple. Four point sources are resolved
in the new, higher-resolution images. We identify one of the sources with the
fading SN. The other three objects are consistent with single supergiant stars.
We conclude that their light contaminated the previously identified progenitor
candidate. After subtraction of these stars, the progenitor appears to be
significantly fainter and bluer than previously measured. Post-explosion
photometry at the SN location indicates that the progenitor object has
disappeared. If single, the progenitor is compatible with a supergiant star of
B to mid-A spectral type, while a Wolf-Rayet (WR) star would be too luminous in
the ultraviolet to account for the observations. Moreover, our hydrodynamical
modelling shows the pre-explosion mass was and the radius was
, which is incompatible with a WR progenitor. We present a
possible interacting binary progenitor computed with our evolutionary models
that reproduces all the observational evidence. A companion star as luminous as
an O9-B0 main-sequence star may have remained after the explosion.Comment: ApJ accepted, 14 pages, 7 figure
Principles of Discrete Time Mechanics: IV. The Dirac Equation, Particles and Oscillons
We apply the principles of discrete time mechanics discussed in earlier
papers to the first and second quantised Dirac equation. We use the Schwinger
action principle to find the anticommutation relations of the Dirac field and
of the particle creation operators in the theory. We find new solutions to the
discrete time Dirac equation, referred to as oscillons on account of their
extraordinary behaviour. Their principal characteristic is that they oscillate
with a period twice that of the fundamental time interval T of our theory.
Although these solutions can be associated with definite charge, linear
momentum and spin, such objects should not be observable as particles in the
continuous time limit. We find that for non-zero T they correspond to states
with negative squared norm in Hilbert space. However they are an integral part
of the discrete time Dirac field and should play a role in particle
interactions analogous to the role of longitudinal photons in conventional
quantum electrodynamics.Comment: 27 pages LateX; published versio
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