The causal structure of dynamical charged black holes

We study the causal structure of dynamical charged black holes, with a sufficient number of massless fields, using numerical simulations. Neglecting Hawking radiation, the inner horizon is a null Cauchy horizon and a curvature singularity due to mass inflation. When we include Hawking radiation, the inner horizon becomes space-like and is separated from the Cauchy horizon, which is parallel to the out-going null direction. Since a charged black hole must eventually transit to a neutral black hole, we studied the neutralization of the black hole and observed that the inner horizon evolves into a space-like singularity, generating a Cauchy horizon which is parallel to the in-going null direction. Since the mass function is finite around the inner horizon, the inner horizon is regular and penetrable in a general relativistic sense. However, since the curvature functions become trans-Planckian, we cannot saymore about the region beyond the inner horizon, and it is natural to say that there is a 'physical' space-like singularity. However, if we assume an exponentially large number of massless scalar fields, our results can be extended beyond the inner horizon. In this case, strong cosmic censorship and black hole complementarity can be violated.Comment: 23 pages, 23 figure

Relationship between temporary emotion of students and performance in learning through comparing facial expression analytics

This paper presents a study on temporary emotion of students and their performance related to learning activities. This paper elucidates different kinds of facial expressions elicited during the activities: quiz and a movie trailer with the help of existing facial expression analyzing applications. The user’s expressions are recorded as video while watching the movie trailer and doing the quiz. The video is processed by different applications which gives the score for different emotions. The results obtained are studied to find which emotion is mostly prevalent among the user in different situations. From this study, it is shown that students experience seemingly different emotions during the activity. The emotions they portrayed were confusion, sadness, anger and neutral. This study explores the use of affective computing for further comprehension of students’ emotion in learning environment

No-boundary measure and preference for large e-foldings in multi-field inflation

The no-boundary wave function of quantum gravity usually assigns only very small probability to long periods of inflation. This was a reason to doubt about the no-boundary wave function to explain the observational universe. We study the no-boundary proposal in the context of multi-field inflation to see whether the number of fields changes the situation. For a simple model, we find that indeed the no-boundary wave function can give higher probability for sufficient inflation, but the number of fields involved has to be very high.Comment: 16 pages, 2 figure

Dynamics of false vacuum bubbles in Brans-Dicke theory

We study the dynamics of false vacuum bubbles in the Brans-Dicke theory of gravity by using the thin shell or thin wall approximation. We consider a false vacuum bubble that has a different value for the Brans-Dicke field between the inside false vacuum region and the outside true vacuum region. Within a certain limit of field values, the difference of field values makes the effective tension of the shell negative. This allows new expanding false vacuum bubbles to be seen by the outside observer, which are disallowed in Einstein gravity.Comment: 29 pages, 20 figure

Dynamical formation and evolution of (2+1)-dimensional charged black holes

In this paper, we investigate the dynamical formation and evolution of 2 + 1-dimensional charged black holes. We numerically study dynamical collapses of charged matter fields in an anti de Sitter background and note the formation of black holes using the double-null formalism. Moreover, we include re-normalized energy-momentum tensors assuming the S-wave approximation to determine thermodynamical back-reactions to the internal structures. If there is no semi-classical effects, the amount of charge determines the causal structures. If the charge is sufficiently small, the causal structure has a space-like singularity. However, as the charge increases, an inner Cauchy horizon appears. If we have sufficient charge, we see a space-like outer horizon and a time-like inner horizon, and if we give excessive charge, black hole horizons disappear. We have some circumstantial evidences that weak cosmic censorship is still satisfied, even for such excessive charge cases. Also, we confirm that there is mass inflation along the inner horizon, although the properties are quite different from those of four-dimensional cases. Semi-classical back-reactions will not affect the outer horizon, but they will affect the inner horizon. Near the center, there is a place where negative energy is concentrated. Thus, charged black holes in three dimensions have two types of curvature singularities in general: via mass inflation and via a concentration of negative energy. Finally, we classify possible causal structures.Comment: 40 pages, 15 figure

Theoretical study of the (3x2) reconstruction of beta-SiC(001)

By means of ab initio molecular dynamics and band structure calculations, as well as using calculated STM images, we have singled out one structural model for the (3x2) reconstruction of the Si-terminated (001) surface of cubic SiC, amongst several proposed in the literature. This is an alternate dimer-row model, with an excess Si coverage of 1/3, yielding STM images in good accord with recent measurements [F.Semond et al. Phys. Rev. Lett. 77, 2013 (1996)].Comment: To be published in PRB Rapid. Com

The no-boundary measure in scalar-tensor gravity

In this article, we study the no-boundary wave function in scalar-tensor gravity with various potentials for the non-minimally coupled scalar field. Our goal is to calculate probabilities for the scalar field - and hence the effective gravitational coupling and cosmological constant - to take specific values. Most calculations are done in the minisuperspace approximation, and we use a saddle point approximation for the Euclidean action, which is then evaluated numerically. We find that for potentials that have several minima, none of them is substantially preferred by the quantum mechanical probabilities. We argue that the same is true for the stable and the runaway solution in the case of a dilaton-type potential. Technically, this is due to the inclusion of quantum mechanical effects (fuzzy instantons). These results are in contrast to the often held view that vanishing gravitation or cosmological constants would be exponentially preferred in quantum cosmology, and they may be relevant to the cosmological constant problem and the dilaton stabilization problem.Comment: 31 pages, 9 figure

The horizon-entropy increase law for causal and quasi-local horizons and conformal field redefinitions

We explicitly prove the horizon-entropy increase law for both causal and quasi-locally defined horizons in scalar-tensor and $f(R)$ gravity theories. Contrary to causal event horizons, future outer trapping horizons are not conformally invariant and we provide a modification of trapping horizons to complete the proof, using the idea of generalised entropy. This modification means they are no longer foliated by marginally outer trapped surfaces but fixes the location of the horizon under a conformal transformation. We also discuss the behaviour of horizons in "veiled" general relativity and show, using this new definition, how to locate cosmological horizons in flat Minkowski space with varying units, which is physically identified with a spatially flat FLRW spacetime.Comment: 23 page

Modeling the series of (n x 2) Si-rich reconstructions of beta-SiC(001): a prospective atomic wire?

We perform ab initio plane wave supercell density functional calculations on three candidate models of the (3 x 2) reconstruction of the beta-SiC(001) surface. We find that the two-adlayer asymmetric-dimer model (TAADM) is unambiguously favored for all reasonable values of Si chemical potential. We then use structures derived from the TAADM parent to model the silicon lines that are observed when the (3 x 2) reconstruction is annealed (the (n x 2) series of reconstructions), using a tight-binding method. We find that as we increase n, and so separate the lines, a structural transition occurs in which the top addimer of the line flattens. We also find that associated with the separation of the lines is a large decrease in the HOMO-LUMO gap, and that the HOMO state becomes quasi-one-dimensional. These properties are qualititatively and quantitatively different from the electronic properties of the original (3 x 2) reconstruction.Comment: 22 pages, including 6 EPS figure