18868106
Are Gamma-Ray Bursts Standard Candles?
By dividing a sample of 48 long-duration gamma-ray bursts (GRBs) into four groups with redshift from low to high and fitting each group with the Amati relation log Eiso = a + b log Epeak, I find that parameters a and b vary with the mean redshift of the GRBs in each group systematically and significantly. The results suggest that GRBs evolve strongly with the cosmic redshift and hence are not standard candles.
11692409
Electromagnetic energy for a charged Kerr black hole in a uniform magnetic field
With the Komar mass formula we calculate the electromagnetic energy for a charged Kerr black hole in a uniform magnetic field. We find that the total electromagnetic energy takes the minimum when the Kerr black hole possesses a nonzero net charge $Q=2\ensuremath{\xi}{B}_{0}{J}_{H}$ where ${B}_{0}$ is the strength of the magnetic field, ${J}_{H}$ is the angular momentum of the black hole, and $\ensuremath{\xi}$ is a dimensionless parameter determined by the spin of the black hole. However, the Wald state with ${Q=2B}_{0}{J}_{H}$ does not minimize the electromagnetic energy.
118518653
Constraining fast radio burst progenitors with gravitational lensing
Fast Radio Bursts (FRBs) are new transient radio sources discovered recently. Because of the angular resolution restriction in radio surveys, no optical counter part has been identified yet so it is hard to determine the progenitor of FRBs. In this paper we propose to use radio lensing survey to constrain FRB progenitors. We show that, different types of progenitors lead to different probabilities for a FRB to be gravitationally lensed by dark matter halos in foreground galaxies, since different type progenitors result in different redshift distributions of FRBs. For example, the redshift distribution of FRBs arising from double stars shifts toward lower redshift than of the FRBs arising from single stars, because double stars and single stars have different evolution timescales. With detailed calculations, we predict that the FRB sample size for producing one lensing event varies significantly for different FRB progenitor models. We argue that this fact can be used to distinguish different FRB models and also discuss the practical possibility of using lensing observation in radio surveys to constrain FRB progenitors.
39373169
Can the universe create itself
The question of first-cause has troubled philosophers and cosmologists alike. Now that it is apparent that our universe began in a Big Bang explosion, the question of what happened before the Big Bang arises. Inflation seems like a very promising answer, but as Borde and Vilenkin have shown, the inflationary state preceding the Big Bang must have had a beginning also. Ultimately, the difficult question seems to be how to make something out of nothing. This paper explores the idea that this is the wrong question --- that that is not how the Universe got here. Instead, we explore the idea of whether there is anything in the laws of physics that would prevent the Universe from creating itself. Because spacetimes can be curved and multiply connected, general relativity allows for the possibility of closed timelike curves (CTCs). Thus, tracing backwards in time through the original inflationary state we may eventually encounter a region of CTCs giving no first-cause. This region of CTCs, may well be over by now (being bounded toward the future by a Cauchy horizon). We illustrate that such models --- with CTCs --- are not necessarily inconsistent by demonstrating self-consistent vacuums for Misner space and a multiply connected de Sitter space in which the renormalized energy-momentum tensor does not diverge as one approaches the Cauchy horizon and solves Einstein's equations. We show such a Universe can be classically stable and self-consistent if and only if the potentials are retarded, giving a natural explanation of the arrow of time. Some specific scenarios (out of many possible ones) for this type of model are described. For example: an inflationary universe gives rise to baby universes, one of which turns out to be itself. Interestingly, the laws of physics may allow the Universe to be its own mother.
11909154
The X‐ray transient 080109 in NGC 2770: an X‐ray flash associated with a normal core‐collapse supernova
Although it is generally thought that long-duration gamma-ray bursts (LGRBs) are associated with core-collapse supernovae (SNe), so far only four pairs of GRBs and SNe with firmly established connection have been found. All the four GRB-SNe belong to special class of Type Ic – called the broad-lined SNe indicative of a large explosion energy, suggesting that only a small fraction of SNe Ibc have GRBs associated with them. This scheme has been refreshed by the discovery of a bright X-ray transient in NGC 2770 on 2008 January 9, which was followed by a rather normal Type Ib SN 2008D. In this paper, I argue that the transient 080109 is an X-ray flash (XRF, the soft version of a GRB) because of the following evidence. (1) The transient cannot be interpreted as a SN shock breakout event. (2) The GRB X-ray flare interpretation is not supported by the high-energy observation. I then show that XRF 080109 satisfies the well-known relation between the isotropic-equivalent energy and the peak spectral energy for LGRBs, which highly strengthens the XRF interpretation. Finally, I point out that the peak spectral energy of XRF 080109 and the maximum bolometric luminosity of SN 2008D agree with the E γ, peak–LSN,max relationship of Li, strengthening the validity of the relationship. I speculate that events like XRF 080109 may occur at a rate comparable to SNe Ibc, and a soft X-ray telescope devoted to surveying for nearby X-ray flares will be very fruitful in discovering them.
10326293
New light on time machines: Against the chronology protection conjecture.
I construct a spacetime with closed timelike curves and without closed causal geodesics. There is a noncompactly generated Cauchy horizon separating the region with closed timelike curves from that without closed causal curves. This spacetime might be stable against the vacuum fluctuation of matter fields. Whether such a spacetime is stable against the vacuum fluctuation of a gravitational field is an open question.
118646964
Large Field Cutoffs in Lattice Gauge Theory
In pure gauge SU(3) near beta = 6, weak and strong coupling expansions break down and the MC method seems to be the only practical alternative. We discuss the possibility of using a modified version of perturbation theory which relies on a large field cutoff and has been successfully applied to the double-well potential (Y. M., PRL 88 141601). Generically, in the case of scalar field theory, the weak coupling expansion is unable to reproduce the exponential suppression of the large field configurations. This problem can be solved by introducing a large field cutoff. The value of this cutoff can be chosen to reduce the discrepancy with the original problem. This optimization can be approximately performed using the strong coupling expansion and bridges the gap between the two expansions. We report recent attempts to extend this procedure for SU(3) gauge theory on the lattice. We compare gauge invariant and gauge dependent (in the Landau gauge) criteria to sort the configurations into ``large-field'' and ``small-field'' configurations. %We discuss the effects of discarding the large field configurations. We discuss the convergence of lattice perturbation theory and the way it can be modified in order to obtain results similar to the scalar case.
119229309
Non-Gaussian features from the inverse volume corrections in loop quantum cosmology
In this paper we study the non-Gaussian features of the primordial fluctuations in loop quantum cosmology with the inverse volume corrections. The detailed analysis is performed in the single field slow-roll inflationary models. However, our results reflect the universal characteristics of bispectrum in loop quantum cosmology. The main corrections to the scalar bispectrum come from two aspects: one is the modifications to the standard Bunch-Davies vacuum, and the other is the corrections to the background dependent variables, such as slow-roll parameters. Our calculations show that the loop quantum corrections make f(NL) of the inflationary models increase 0.1%. Moreover, we find that two new shapes of non-Gaussian signal arise, which we name F-1 and F-2. The former gives a unique loop quantum feature, which is less correlated with the local, equilateral, and single types, while the latter is highly correlated with the local one.
119184187
Holographic entanglement entropy in P-wave superconductor phase transition
A bstractWe investigate the behavior of entanglement entropy across the holographic p-wave superconductor phase transition in an Einstein-Yang-Mills theory with a negative cosmological constant. The holographic entanglement entropy is calculated for a strip geometry at AdS boundary. It is found that the entanglement entropy undergoes a dramatic change as we tune the ratio of the gravitational constant to the Yang-Mills coupling, and that the entanglement entropy does behave as the thermal entropy of the background black holes. That is, the entanglement entropy will show the feature of the second order or first order phase transition when the ratio is changed. It indicates that the entanglement entropy is a good probe to investigate the properties of the holographic phase transition.
119203321
STATISTICAL PROPERTIES OF MULTIPLE OPTICAL EMISSION COMPONENTS IN GAMMA-RAY BURSTS AND IMPLICATIONS
Well-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are complied from the literature. Multiple optical emission components are extracted with power-law function fits to these lightcurves. We present a systematical analysis for statistical properties and their relations to prompt gamma-ray emission and X-ray afterglow for each component. We show that peak luminosity in the prompt and late flares are correlated and the evolution of the peak luminosity may signal the evolution of the accretion rate. No tight correlation between the shallow decay phase/plateau and prompt gamma-ray emission is found. Assuming that they are due to a long-lasting wind injected by a compact object, we show that the injected behavior favors the scenarios of a long-lasting wind powered by a Poynting flux from a black hole via the Blandford-Znajek mechanism fed by fall-back mass or by the spin-down energy release of a magnetar after the main burst episode. The peak luminosity of the afterglow onset is tightly correlated ...
119180645
Binary interactions and UV photometry on photometric redshift
Using the Hyperz code (Bolzonella et al . 2000) we present photometric redshift estimates for a random sample of galaxies selected from the SDSS/DR7 and GALEX/DR4, for which spectroscopic redshifts are also available. We confirm that the inclusion of ultraviolet photometry improves the accuracy of photo- z s for those galaxies with g * – r * ≤ 0.7 and z spec ≤ 0.2. We also address the problem of how binary interactions can affect photo- z estimates, and find that their effect is negligible.