Global Neutrino Heating in Hyperaccretion Flows

The neutrino-dominated accretion flow (NDAF) with accretion rates \dot{M} = 0.01 - 10 M_{\sun} s^{-1} is a plausible candidate for the central engine of gamma-ray bursts (GRBs). This hyperaccretion disk is optically thin to neutrinos in the radial direction, therefore the neutrinos produced at one radius can travel for a long distance in the disk. Those neutrinos can thus be absorbed with certain probability by the disk matter at the other radius and heat the disk there. The effect of this "global neutrino heating" has been ignored in previous works and is the focus of this paper. We find that around the "ignition" radius r_{ign}, the global neutrino heating rate could be comparable to or even larger than the local viscous heating rate thus must be an important process. Two possible consequences are in order if the "global neutrino heating" is taken into account: i) the temperature of the disk is slightly raised and the "ignition" radius r_{ign} slightly shifts to a larger radius, both lead to the increasing of the total neutrino flux; ii) what is more interesting is that, the temperature of the ADAF just beyond r_{ign} may be raised above the virial temperature thus the accretion will be suppressed. In this case, the activity of the black hole is expected to oscillate between an active and inactive phases. The timescale of the active phases is estimated to be \sim 1 second. If the timescale of the inactive phase is comparable to or less than this value, this intermittent activity may explain the slow variability component of the GRBs. Self-consistent global calculations of NDAFs with the "global neutrino heating" included are required in the future to more precisely evaluate this effect.Comment: 9 pages, 5 figures; more discussions and references added; accepted for publication in MNRA

Josephson junction on one edge of a two dimensional topological insulator affected by magnetic impurity

Current-phase relation in a Josephson junction formed by putting two s-wave superconductors on the same edge of a two dimensional topological insulator is investigated. We consider the case that the junction length is finite and magnetic impurity exists. The similarity and difference with conventional Josephson junction is discussed. The current is calculated in the semiconductor picture. Both the $2\pi$- and $4\pi$-period current-phase relations ($I_{2\pi}(\phi), I_{4\pi}(\phi)$) are studied. There is a sharp jump at $\phi=\pi$ and $\phi=2\pi$ for $I_{2\pi}$ and $I_{4\pi}$ respectively in the clean junction. For $I_{2\pi}$, the sharp jump is robust against impurity strength and distribution. However for $I_{4\pi}$, the impurity makes the jump at $\phi=2\pi$ smooth. The critical (maximum) current of $I_{2\pi}$ is given and we find it will be increased by asymmetrical distribution of impurity.Comment: 7 pages, 5 figure

Bipolaronic blockade effect in quantum dots with negative charging energy

We investigate single-electron transport through quantum dots with negative charging energy induced by a polaronic energy shift. For weak dot-lead tunnel couplings, we demonstrate a bipolaronic blockade effect at low biases which suppresses the oscillating linear conductance, while the conductance resonances under large biases are enhanced. Novel conductance plateau develops when the coupling asymmetry is introduced, with its height and width tuned by the coupling strength and external magnetic field. It is further shown that the amplitude ratio of magnetic-split conductance peaks changes from 3 to 1for increasing coupling asymmetry. Though we demonstrate all these transport phenomena in the low-order single-electron tunneling regime, they are already strikingly different from the usual Coulomb blockade physics and are easy to observe experimentally.Comment: 6 pages, 5 figure

Rainbow gravity corrections to the entropic force

The entropic force attracts a lot of interest for its multifunctional properties. For instance, Einstein's field equation, Newton's law of gravitation and the Friedmann equation can be derived from the entropic force. In this paper, utilizing a new kind of rainbow gravity model that was proposed by Magueijo and Smolin, we explore the quantum gravity corrections to the entropic force. First, we derive the modified thermodynamics of a rainbow black hole via its surface gravity. Then, according to Verlinde's theory, the quantum corrections to the entropic force are obtained. The result shows that the modified entropic force is related not only to the properties of the black hole but also the Planck length $\ell_p$, and the rainbow parameter $\gamma$. Furthermore, based on the rainbow gravity corrected entropic force, the modified Einstein's field equation and the modified Friedmann equation are also derived.Comment: 10 page

Thermodynamic phase transition of a black hole in rainbow gravity

In this letter, using the rainbow functions that were proposed by Magueijo and Smolin, we investigate the thermodynamics and the phase transition of rainbow Schwarzschild black hole. First, we calculate the rainbow gravity corrected Hawking temperature. From this modification, we then derive the local temperature, free energy, and other thermodynamic quantities in an isothermal cavity. Finally, we analyze the critical behavior, thermodynamic stability, and phase transition of the rainbow Schwarzschild black hole. The results show that the rainbow gravity can stop the Hawking radiation in the final stages of black holes' evolution and lead to the remnants of black holes. Furthermore, one can observe that the rainbow Schwarzschild black hole has one first-order phase transition, two second-order phase transitions, and three Hawking-Page-type phase transitions in the framework of rainbow gravity theory.Comment: 7 pages, 3 figures, accepted for publication in Physical Letter B. arXiv admin note: substantial text overlap with arXiv:1608.0682

Thermal entanglement in a two-spin-qutrit system under a nonuniform external magnetic field

The thermal entanglement in a two-spin-qutrit system with two spins coupled by exchange interaction under a magnetic field in an arbitrary direction is investigated. Negativity, the measurement of entanglement, is calculated. We find that for any temperature the evolvement of negativity is symmetric with respect to magnetic field. The behavior of negativity is presented for four different cases. The results show that for different temperature, different magnetic field give maximum entanglement. Both the parallel and antiparallel magnetic field cases are investigated qualitatively (not quantitatively) in detail, we find that the entanglement may be enhanced under an antiparallel magnetic field.Comment: 2 eps figure