44433480
Two open universes connected by a wormhole: Exact solutions
Abstract In this paper, I present a space–time of two open universes connected by a Lorentzian wormhole. The space–time has the following features: (1) it can exactly solve the Einstein equations; (2) the weak energy condition is satisfied everywhere; (3) it has a topology of R 2 × T g ( g ≥2); (4) it has no event horizons.
13023795
Extracting Energy from a Black Hole through the Transition Region
A new scenario for extracting energy from a Kerr black hole is proposed. With magnetic field lines connecting plasma particles inside the ergosphere with remote loads, the frame dragging twists the field lines so that energy and angular momentum are extracted from the plasma particles. If the magnetic field is strong enough, the energy extracted from the particles can be so large that the particles have negative energy as they fall into the black hole. So, effectively, the energy is extracted from the black hole. The particles inside the ergosphere can be continuously replenished with accretion from a disk surrounding the black hole, so a transition region with a sufficient amount of plasma is formed between the black hole's horizon and the inner edge of the disk. Thus, the energy can be continuously extracted from the black hole through the transition region. This may be the most efficient way for extracting energy from a Kerr black hole: in principle, almost all of the rotational energy (up to ≈29% of the total energy of the black hole) can be extracted.
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.
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.
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.
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.
119743724
Quantum correlation and phase transitions in a two-dimensional doubly decorated Ising-Heisenberg model
We investigate the pairwise quantum correlation, characterized by quantum entanglement (QE) and quantum discord (QD), of a two-dimensional Ising-Heisenberg model on a planar doubly decorated lattice. At zero temperature, the concurrence (a measurement of pairwise entanglement) and the QD are related to the correlation function qxx and the staggered magnetization δSz, respectively, and both of them indicate the quantum phase transition (QPT) of the system. However, in a finite-temperature phase transition, all the pairwise entanglement vanishes thus it fails to detect the critical temperature TC, while the derivative of QD diverges at TC. This shows clearly that QD can capture the signal of phase transition in a separable state, thus it has a broader scope of application than QE in detecting phase transitions.
119231659
The effects of ultraviolet photometry and binary interactions on photometric redshift and galaxy morphology
Using the HYPERZ code and a template spectral library, which consists of four observed galaxy spectra from Coleman, Wu & Weedman (CWW) and eight spectral families built with evolutionary population synthesis models, we present photometric redshift (photo-z) estimates for a spectroscopic sample of 6531 galaxies. Spectroscopic redshifts are also available, and are selected from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) and the Galaxy Evolution Explorer (GALEX) Data Release 4 (DR4). There are also morphologies for a morphological sample of 1502 bright galaxies, which are from the catalogue of Fukugita et al., and these are also matched with SDSS DR7 and GALEX DR4. We find that the inclusion of F(UV) or N(UV), or both, decreases the number of catastrophic identifications (| z.(phot) - z.(spec)| > 1.0). If catastrophic identifications are removed, the inclusion of both FUV and NUV photometry mainly increases the number of non-catastrophic identifications in the low-redshift, g-r less than or similar to 0.8 and fainter r-magnitude regions. The inclusion of binary interactions mainly increases the number of non-catastrophic identifications and decreases the deviations in the 0.3 <= g-r <= 0.8 region when only using optical photometry. Based on the morphological galaxy sample, we find that the inclusion of ultraviolet (UV) photometry decreases and increases the probability that early types are classified as burst and E types, respectively. This increases the probability that late types are classified as CWW-Sbc and CWW-Scd types. If catastrophic identifications are excluded, the inclusion of UV data mainly increases the identifications of late types in all redshift, bluer g-r and r greater than or similar to 14 regions. Moreover, binary interactions mainly affect the determinations of E and S0 types. In comparison, we find that the reliability and completeness for early-and late-type selection by the HYPERZ code are less than those by the concentration index C = 2.6, the profile likelihood P(exp) - P(de)V = 0 and colour u-r = 2.22 criteria. Moreover, we find that N(UV)-u = 1.94 and 5.77 - 1.47(u-r) = F(UV)-u discriminators can be used as morphology selection indicators. These two criteria have comparable reliability and completeness for selecting early- and late-type galaxies to C = 2.6 criterion and higher completeness for early-type selection than the u-r = 2.22 criterion.
119155218
A holographic p-wave superconductor model
A bstractWe study a holographic p-wave superconductor model in a four dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. The complex vector field is charged under the Maxwell field. We solve the full coupled equations of motion of the system and find black hole solutions with the vector hair. The vector hairy black hole solutions are dual to a thermal state with the U(1) symmetry as well as the spatial rotational symmetry broken spontaneously. Depending on two parameters, the mass and charge of the vector field, we find a rich phase structure: zeroth order, first order and second order phase transitions can happen in this model. We also find “retrograde condensation” in which the hairy black hole solution exists only for the temperatures above a critical value with the free energy much larger than the one of the black hole without the vector hair. We construct the phase diagram for this system in terms of the temperature and charge of the vector field.
118706095
Non-relativistic fluid dual to asymptotically AdS gravity at finite cutoff surface
Using the non-relativistic hydrodynamic limit, we solve equations of motion for Einstein gravity and Gauss-Bonnet gravity with a negative cosmological constant within the region between a finite cutoff surface and a black brane horizon, up to second order of the non-relativistic hydrodynamic expansion parameter. Through the Brown-York tensor, we calculate the stress energy tensor of dual fluids living on the cutoff surface. With the black brane solutions, we show that for both Einstein gravity and Gauss-Bonnet gravity, the ratio of shear viscosity to entropy density of dual fluid does not run with the cutoff surface. The incompressible Navier-Stokes equations are also obtained in both cases.
119393533
Mass formulas and thermodynamic treatment in the mass-density-dependent model of strange quark matter
The previous treatments for strange quark matter in the quark mass-density-dependent model have unreasonable vacuum limits. We provide a method to obtain the quark mass parametrizations and give a self-consistent thermodynamic treatment which includes the MIT bag model as an extreme. In this treatment, strange quark matter in bulk still has the possibility of absolute stability. However, the behavior of the sound velocity is opposite to previous findings.