1,289 research outputs found
Do Newton's G and Milgrom's a_0 vary with cosmological epoch ?
In the scalar tensor gravitational theories Newton's constant G_N evolves in
the expanding universe. Likewise, it has been speculated that the acceleration
scale a_0 in Milgrom's modified Newtonian dynamics (MOND) is tied to the scale
of the cosmos, and must thus evolve. With the advent of relativistic
implementations of the modified dynamics, one can address the issue of
variability of the two gravitational ''constants'' with some confidence. Using
TeVeS, the Tensor-Vector-Scalar gravitational theory, as an implementation of
MOND, we calculate the dependence of G_N and a_0 on the TeVeS parameters and
the coeval cosmological value of its scalar field, \phi_c. We find that G_N,
when expressed in atomic units, is strictly nonevolving, a result fully
consistent with recent empirical limits on the variation of G_N. By contrast,
we find that a_0 depends on \phi_c and may thus vary with cosmological epoch.
However, for the brand of TeVeS which seems most promising, a_0 variation
occurs on a timescale much longer than Hubble's, and should be imperceptible
back to redshift unity or even beyond it. This is consistent with emergent data
on the rotation curves of disk galaxies at significants redshifts.Comment: 9 pages, RevTe
Black Hole Thermodynamics and Lorentz Symmetry
Recent developments point to a breakdown in the generalized second law of
thermodynamics for theories with Lorentz symmetry violation. It appears
possible to construct a perpetual motion machine of the second kind in such
theories, using a black hole to catalyze the conversion of heat to work. Here
we describe and extend the arguments leading to that conclusion. We suggest the
inference that local Lorentz symmetry may be an emergent property of the
macroscopic world with origins in a microscopic second law of causal horizon
thermodynamics.Comment: 4 pages; v2: Version to appear in Foundations of Physics. Potential
counterexamples addressed, argument given applying to LV theories where all
speeds (or horizons) coincide, and editing for clarit
Precursors prior to Type IIn supernova explosions are common: precursor rates, properties, and correlations
There is a growing number of supernovae (SNe), mainly of Type IIn, which
present an outburst prior to their presumably final explosion. These precursors
may affect the SN display, and are likely related to some poorly charted
phenomena in the final stages of stellar evolution. Here we present a sample of
16 SNe IIn for which we have Palomar Transient Factory (PTF) observations
obtained prior to the SN explosion. By coadding these images taken prior to the
explosion in time bins, we search for precursor events. We find five Type IIn
SNe that likely have at least one possible precursor event, three of which are
reported here for the first time. For each SN we calculate the control time.
Based on this analysis we find that precursor events among SNe IIn are common:
at the one-sided 99% confidence level, more than 50% of SNe IIn have at least
one pre-explosion outburst that is brighter than absolute magnitude -14, taking
place up to 1/3 yr prior to the SN explosion. The average rate of such
precursor events during the year prior to the SN explosion is likely larger
than one per year, and fainter precursors are possibly even more common. We
also find possible correlations between the integrated luminosity of the
precursor, and the SN total radiated energy, peak luminosity, and rise time.
These correlations are expected if the precursors are mass-ejection events, and
the early-time light curve of these SNe is powered by interaction of the SN
shock and ejecta with optically thick circumstellar material.Comment: 15 pages, 20 figures, submitted to Ap
NMR characterization of spin-1/2 alternating antiferromagnetic chains in the high-pressure phase of (VO)2P2O7
Local-susceptibility measurements via the NMR shifts of P and V
nuclei in the high-pressure phase of (VO)PO confirmed the
existence of a unique alternating antiferromagnetic chain with a zero-field
spin gap of 34 K. The P nuclear spin-lattice relaxation rate scales with
the uniform spin susceptibility below about 15 K which shows that the
temperature dependence of both the static and dynamical spin susceptibilities
becomes identical at temperatures not far below the spin-gap energy.Comment: 6 pages, 5 figures; To be published in J. Phys. Condens. Matte
SN2010jp (PTF10aaxi): A Jet-Driven Type II Supernova
We present photometry and spectroscopy of the peculiar TypeII supernova (SN)
2010jp, also named PTF10aaxi. The light curve exhibits a linear decline with a
relatively low peak absolute magnitude of only -15.9, and a low radioactive
decay luminosity at late times that suggests a nickel mass below 0.003
. Spectra of SN2010jp display an unprecedented triple-peaked
H line profile, showing: (1) a narrow (800 km/s) central component that
suggests shock interaction with dense CSM; (2) high-velocity blue and red
emission features centered at -12600 and +15400 km/s; and (3) broad wings
extending from -22000 to +25000 km/s. These features persist during 100 days
after explosion. We propose that this line profile indicates a bipolar
jet-driven explosion, with the central component produced by normal SN ejecta
and CSM interaction at mid latitudes, while the high-velocity bumps and broad
line wings arise in a nonrelativistic bipolar jet. Two variations of the jet
interpretation seem plausible: (1) A fast jet mixes 56Ni to high velocities in
polar zones of the H-rich envelope, or (2) the reverse shock in the jet
produces blue and red bumps in Balmer lines when a jet interacts with dense
CSM. Jet-driven SNeII are predicted for collapsars resulting from a wide range
of initial masses above 25 at sub-solar metallicity. This seems
consistent with the SN host environment, which is either an extremely
low-luminosity dwarf galaxy or very remote parts of an interacting pair of
star-forming galaxies. It also seems consistent with the low 56Ni mass that may
accompany black hole formation. We speculate that the jet survives to produce
observable signatures because the star's H envelope was mostly stripped away by
previous eruptive mass loss.Comment: 11 pages, 9 figures, submitted to MNRA
Identification of Nuclear Relaxation Processes in a Gapped Quantum Magnet: Proton NMR in the S=1/2 Heisenberg Ladder Cu2(C5H12N2)2Cl4
The proton hyperfine shift K and NMR relaxation rate have been
measured as a function of temperature in the S=1/2 Heisenberg antiferromagnetic
ladder Cu2(C5H12N2)2Cl4. The presence of a spin gap in this strongly coupled ladder ()
is supported by the K and results. By comparing at two
different proton sites, we infer the evolution of the spectral functions
and . When the gap is significantly
reduced by the magnetic field, two different channels of nuclear relaxation,
specific to gapped antiferromagnets, are identified and are in agreement with
theoretical predictions.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Letter
Slow-Speed Supernovae from the Palomar Transient Factory: Two Channels
Since the discovery of the unusual prototype SN 2002cx, the eponymous class
of low-velocity, hydrogen-poor supernovae has grown to include at most another
two dozen members identified from several heterogeneous surveys, in some cases
ambiguously. Here we present the results of a systematic study of 1077
hydrogen-poor supernovae discovered by the Palomar Transient Factory, leading
to nine new members of this peculiar class. Moreover we find there are two
distinct subclasses based on their spectroscopic, photometric, and host galaxy
properties: The "SN 2002cx-like" supernovae tend to be in later-type or more
irregular hosts, have more varied and generally dimmer luminosities, have
longer rise times, and lack a Ti II trough when compared to the "SN
2002es-like" supernovae. None of our objects show helium, and we counter a
previous claim of two such events. We also find that these transients comprise
5.6+17-3.7% (90% confidence) of all SNe Ia, lower compared to earlier
estimates. Combining our objects with the literature sample, we propose that
these subclasses have two distinct physical origins.Comment: 49 pages, 36 figures, submitted to Ap
Free Energy of an Inhomogeneous Superconductor: a Wave Function Approach
A new method for calculating the free energy of an inhomogeneous
superconductor is presented. This method is based on the quasiclassical limit
(or Andreev approximation) of the Bogoliubov-de Gennes (or wave function)
formulation of the theory of weakly coupled superconductors. The method is
applicable to any pure bulk superconductor described by a pair potential with
arbitrary spatial dependence, in the presence of supercurrents and external
magnetic field. We find that both the local density of states and the free
energy density of an inhomogeneous superconductor can be expressed in terms of
the diagonal resolvent of the corresponding Andreev Hamiltonian, resolvent
which obeys the so-called Gelfand-Dikii equation. Also, the connection between
the well known Eilenberger equation for the quasiclassical Green's function and
the less known Gelfand-Dikii equation for the diagonal resolvent of the Andreev
Hamiltonian is established. These results are used to construct a general
algorithm for calculating the (gauge invariant) gradient expansion of the free
energy density of an inhomogeneous superconductor at arbitrary temperatures.Comment: REVTeX, 28 page
Nuclear Magnetic Relaxation in the Haldane-Gap Antiferromagnet Ni(C_2_H_8_N_2_)_2_NO_2_(ClO_4_)
A new theory is proposed to interpret nuclear spin-lattice relaxation-time
(T_1_) measurements on the spin-1 quasi-one-dimensional Heisenberg
antiferromagnet Ni(C_2_H_8_N_2_)_2_NO_2_(ClO_4_) (NENP). While Sagi and Affleck
pioneeringly discussed this subject in terms of field-theoretical languages,
there is no theoretical attempt yet to explicitly simulate the novel
observations of 1/T_1_ reported by Fujiwara et al.. By means of modified spin
waves, we solve the minimum of 1/T_1_ as a function of an applied field,
pending for the past decade.Comment: to be published in J. Phys. Soc. Jpn. 73, No. 4 (2004
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