Massless vs. Massive Hawking Radiation in AdS2_2 Spacetime

We study massless and massive Hawking radiations on a two-dimensional AdS spacetime. For the massless case, the quantum stress-energy tensor of a massless scalar field on the AdS background is calculated, and the expected null radiation is obtained. However, for the massive case, the scattering analysis is performed in order to calculate the absorption and reflection coefficients which are related to statistical Hawking temperature. On the contrary to the massless case, we obtain a nonvanishing massive radiation.Comment: 13 pages, revtex, to appear in Phys. Lett.

Toward Bound-State Approach to Strangeness in Holographic QCD

An approach to realize a hyperon as a bound-state of a two-flavor baryon and a kaon is considered in the context of the Sakai-Sugimoto model of holographic QCD, which approach has been known in the Skyrme model as the bound-state approach to strangeness. As a simple case of study, pseudo-scalar kaon is considered as fluctuation around a baryon. In this case, strongly-bound hyperon-states are absent, different from the case of the Skyrme model. Observed is a weak bound-state which would correspond to \Lambda(1405).Comment: 13 pages, 2 figures, v2: references adde

Age differences in social comparison tendency and personal relative deprivation

We examined age-related differences in social comparison orientation and personal relative deprivation (PRD). In Study 1, participants (N = 1,290) reported their tendencies to engage in social comparisons and PRD. Older adults reported lower levels of social comparison tendency and PRD, and social comparison tendency mediated the relation between age and PRD. The findings reported in Study 1 were replicated in Study 2 using a sample of participants between the ages of 18 to 30 (n = 180) and 60+ years old (n = 176). Our findings provide evidence that older adults report lower levels of social comparison tendency that, in turn, relate to lower levels of PRD.This research was funded by a grant from the Leverhulme Trust (RPG-2013-148).This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.paid.2015.08.00

Accelerating universe in two-dimensional noncommutative dilaton cosmology

We show that the phase transition from the decelerating universe to the accelerating universe, which is of relevance to the cosmological coincidence problem, is possible in the semiclassically quantized two-dimensional dilaton gravity by taking into account the noncommutative field variables during the finite time. Initially, the quantum-mechanically induced energy from the noncommutativity among the fields makes the early universe decelerate and subsequently the universe is accelerating because the dilaton driven cosmology becomes dominant later.Comment: 14 pages, 2 figures; to appear in Phys. Lett.

Geometric Gravitational Forces on Particles Moving in a Line

In two-dimensional space-time, point particles can experience a geometric, dimension-specific gravity force, which modifies the usual geodesic equation of motion and provides a link between the cosmological constant and the vacuum $\theta$-angle. The description of such forces fits naturally into a gauge theory of gravity based on the extended Poincar\'e group, {\it i.e.\/} ``string-inspired'' dilaton gravity.Comment: 10 pages, CTP#214

Dilaton driven Hawking radiation in AdS2_2 black hole

A recent study shows that Hawking radiation of the massless scalar field does not appear on the two-dimensional AdS$_2$ black hole background. We study this issue by investigating absorption and reflection coefficients under dilaton coupling with the matter field. If the scalar field does not couple to the dilaton, then it is fully absorbed into the black hole without any outgoing mode. On the other hand, once it couples to the dilaton field, the outgoing mode of the massless scalar field exists and the nontrivial Hawking radiation is obtained. Finally, we comment on this dilaton dependence of Hawking radiation in connection with a three-dimensional black hole.Comment: 13 pages, revtex, no figures, version to appear in Phys. Lett.

Geometry of T-duality

A "reduced" differential geometry adapted to the presence of abelian isometries is constructed.Classical T-duality diagonalizes in this setting, allowing us to get conveniently the transformation of the relevant geometrical objects such as connections, pullbacks and generalized curvatures.Moreover we can induce privileged maps from the viewpoint of the covariant derivatives in the target-space and in the world-sheet generalizing previous results, at the same time that we can correct connections and curvatures covariantly in order to have a proper transformation under T-duality.Comment: Latex, 18 page

Absorption of fixed scalar in scattering off 4D N=4 black holes

We perform the perturbation analysis of the black holes in the 4D, N=4 supergravity. Analysis around the black holes reveals a complicated mixing between the dilaton and other fields (metric and two U(1) Maxwell fields). It turns out that considering both s-wave (l=0) and higher momentum modes (l \neq 0), the dilaton as a fixed scalar is the only propagating mode with $P=Q, h_1=h_2=0$ and $F = -G = 2\phi$. We calculate the absorption cross-section for scattering of low frequency waves of fixed scalar and U(1) Maxwell fields off the extremal black hole.Comment: 11 pages in RevTeX, no figures, minor correction is included(third version

The origin of noncommutativity?

Consistent boundary Poisson structures for open string theory coupled to background $B$-field are considered using the new approach proposed in hep-th/0111005. It is found that there are infinitely many consistent Poisson structures, each leads to a consistent canonical quantization of open string in the presence of background $B$-field. Consequently, whether the $D$-branes to which the open string end points are attached is noncommutative or not depends on the choice of a particular Poisson structure.Comment: Revtex4, published versio

Black Holes in Matrix Theory

We review recent progress in understanding black hole structure and dynamics via matrix theory.Comment: 7 pages, latex; (uses espcrc2.sty). Talk by the second author, presented at STRINGS97 (Amsterdam, June 16-20, 1997)