15632846
Energetics of a Black Hole-Accretion Disk System with Magnetic Connection: Limit of Low Accretion Rate
We consider the energetics of a black hole-accretion disk system with magnetic connection: a Keplerian disk is connected to a Kerr black hole by a large-scale magnetic field. We assume that 1) the magnetic field is locked to the inner boundary of the disk and corotates with it, and 2) the accretion rate is low, but the accretion from the disk can still provide a sufficient amount of cold plasma particles in the transition region so that the magnetohydrodynamics approximation is valid. By finding solutions that smoothly pass the fast critical point near the equatorial plane, we find that a system with a fast rotating black hole and that with a slow rotating black hole behave very differently. For ab lack hole with a>a cr ≡ 0.3594 M ,w hereM is the mass and a is the specific angular momentum of the black hole, the spinning energy of the black hole is efficiently extracted and transported to the disk, thus increasing the radiation efficiency of the disk by orders of magnitude. For a black hole with 0 ≤ a<a cr, the inner region of the disk is disrupted by the magnetic field and the inner boundary moves out to a radius where the angular velocity of the disk is equal to the spinning angular velocity of the black hole. As a result, the disk may have an extremely low radiation efficiency if 0 ≤ a/M � 1.
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.
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.
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.
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.
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.
119108763
Magnetic field effect on the phase transition in AdS soliton spacetime
We investigate the scalar perturbations in an anti-de Sitter soliton background coupled to a Maxwell field via marginally stable modes. In the probe limit, we study the magnetic field effect on the holographic insulator/superconductor phase transition numerically and analytically. The condensate will be localized in a finite circular region for any finite constant magnetic field. Near the critical point, we find that there exists a simple relation among the critical chemical potential, magnetic field, the charge, and mass of the scalar field. This relation indicates that the presence of the magnetic field causes the transition from insulator to superconductor to be difficult.
122891080
THE GENERALIZED CHAPLYGIN GAS MODEL WITH INTERACTION
A two-fluid generalized Chaplygin gas (GCG) model including two different cases is considered in this paper. Concretely, the evolution of the GCG model with interaction is discussed and the statefinder diagnostic for the GCG models is performed, respectively. By analysis, we show that the effective state parameter of dark energy can cross the so-called phantom divide ω = -1, the behavior of GCG will be like ΛCDM in the future and therefore our Universe will not end up with the Big Rip in the future. In addition, we find that the statefinder diagnostic can differentiate the GCG model with or without interaction. Also, trajectories of both the GCG model mixed with cold dark matter (CDM) and the pure GCG model in the parameter plane are illustrated to be significantly different.
119226741
Spectroscopic factors for low-lying $^{16}$N levels and the astrophysical $^{15}$N $(n,\gamma)^{16}$N reaction rate
Fluorine is a key element for nucleosynthetic studies since it is extremely sensitive to the physical conditions within stars. The astrophysical site to produce fluorine is suggested to be asymptotic giant branch (AGB) stars. In these stars the 15N(n, g)16N reaction could affect the abundance of fluorine by competing with 15N(a, g)19F. The 15N(n, g)16N reaction rate depends directly on the neutron spectroscopic factors of the low-lying states in 16N. The angular distributions of the 15N(7Li, 6Li)16N reaction populating the ground state and the first three excited states in 16N are measured using a Q3D magnetic spectrograph and are used to derive the spectroscopic factors of these states based on distorted wave Born approximation (DWBA) analysis. The spectroscopic factors of these four states are extracted to be 0.96+-0.09, 0.69+-0.09, 0.84+-0.08 and 0.65+-0.08, respectively. Based on the new spectroscopic factors we derive the 15N(n,g)16N reaction rate. The accuracy and precision of the spectroscopic factors are enhanced due to the first application of high-precision magnetic spectrograph for resolving the closely-spaced 16N levels which can not be achieved in most recent measurement. The present result demonstrates that two levels corresponding to neutron transfers to the 2s1/2 orbit in 16N are not so good single-particle levels although 15N is a closed neutron-shell nucleus. This finding is contrary to the shell model expectation. The present work also provides an independent examination to shed some light on the existing discrepancies in the spectroscopic factors and the 15N(n, g)16N rate.
118459896
Correlating Quasi{Electron Relaxation with Quantum Femtosecond Magnetism in the Order Parameter Dynamics of Insulating Manganites
Institute of Electronic Structure & Laser, Foundation for Research and Technology{Hellas,Vassilika Vouton, 71110 Heraklion, Crete, Greece(Dated: September 8, 2014)Femtosecond (fs){resolved simultaneous measurements of charge and spin dynamics reveal the co-existence of two di erent quasi{particle excitations in colossal magneto-resistive (CMR) manganites,with fs and ps relaxation times respectively. Their populations reverse size above a photoexcitation{intensity{threshold coinciding with a \sudden" antiferro{to{ferromagnetic switching during <100 fslaser pulses. We present evidence that fast, metallic, mobile quasi{electrons dressed by quantum spinuctuations coexist with slow, localized, polaronic charge carriers in non{equilibrium phases. Thismay be central to CMR transition and leads to a laser{driven charge reorganization simultaneouslywith quantum fs magnetism via an emergent quantum{spin/charge/lattice transient coupling.
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.