Relation between phase and dwell times for quantum tunneling of a relativistically propagating particle

The general and explicit relation between the phase time and the dwell time for quantum tunneling of a relativistically propagating particle is investigated and quantified. In analogy with previously obtained non-relativistic results, it is shown that the group delay can be described in terms of the dwell time and a self-interference delay. Lessons concerning the phenomenology of the relativistic tunneling are drawn

Conditional entropy of glueball states

The conditional entropy of glueball states is calculated using a holographic description. Glueball states are represented by a supergravity dual picture, consisting of a 5-dimensional graviton-dilaton action of a dynamical holographic AdS/QCD model. The conditional entropy is studied as a function of the glueball spin and of the mass, providing information about the stability of the glueball states.Comment: 6 pages, 4 figure

The X-ray light curve of Gamma-ray bursts: clues to the central engine

We present the analysis of a large sample of gamma-ray burst (GRB) X-ray light curves in the rest frame to characterise their intrinsic properties in the context of different theoretical scenarios. We determine the morphology, time scales, and energetics of 64 long GRBs observed by \emph{Swift}/XRT \emph{without} flaring activity. We furthermore provide a one-to-one comparison to the properties of GRBs \emph{with} X-ray flares. We find that the steep decay morphology and its connection with X-ray flares favour a scenario in which a central engine origin. We show that this scenario can also account for the shallow decay phase, provided that the GRB progenitor star has a self-similar structure with a constant envelope-to-core mass ratio $\sim 0.02-0.03$. However, difficulties arise for very long duration ($t_p\gtrsim10^4$ s) shallow phases. Alternatively, a spinning-down magnetar whose emitted power refreshes the forward shock can quantitatively account for the shallow decay properties. In particular we demonstrate that this model can account for the plateau luminosity vs. end time anticorrelation.Comment: 12 pages, 8 figures, accepted for publication in A&

Macroscopic polarization and band offsets at nitride heterojunctions

Ab initio electronic structure studies of prototypical polar interfaces of wurtzite III-V nitrides show that large uniform electric fields exist in epitaxial nitride overlayers, due to the discontinuity across the interface of the macroscopic polarization of the constituent materials. Polarization fields forbid a standard evaluation of band offsets and formation energies: using new techniques, we find a large forward-backward asymmetry of the offset (0.2 eV for AlN/GaN (0001), 0.85 eV for GaN/AlN (0001)), and tiny interface formation energies.Comment: RevTeX 4 pages, 2 figure

Accurate calculation of polarization-related quantities in semiconductors

We demonstrate that polarization-related quantities in semiconductors can be predicted accurately from first-principles calculations using the appropriate approach to the problem, the Berry-phase polarization theory. For III-V nitrides, our test case, we find polarizations, polarization differences between nitride pairs, and piezoelectric constants quite close to their previously established values. Refined data are nevertheless provided for all the relevant quantities.Comment: RevTeX 4 pages, no figure