118387184
Higher order WKB corrections to black hole entropy in brick wall formalism
We calculate the statistical entropy of a quantum field with an arbitrary spin propagating on the spherical symmetric black hole background by using the brick wall formalism at higher orders in the WKB approximation. For general spins, we find that the correction to the standard Bekenstein–Hawking entropy depends logarithmically on the area of the horizon. Furthermore, we apply this analysis to the Schwarzschild and Schwarzschild–AdS(dS) black holes and discuss our results.
119246679
Modified dispersion relations and the response of the rotating Unruh-DeWitt detector
We study the response of a rotating monopole detector that is coupled to a massless scalar field which is described by a nonlinear dispersion relation in flat spacetime. Since it does not seem to be possible to evaluate the response of the rotating detector analytically, we resort to numerical computations. Interestingly, unlike the case of the uniformly accelerated detector that has been considered recently, we find that defining the transition probability rate of the rotating detector poses no difficulties. Further, we show that the response of the rotating detector can be computed exactly (albeit, numerically) even when it is coupled to a field that is governed by a nonlinear dispersion relation. We also discuss the response of the rotating detector in the presence of a cylindrical boundary on which the scalar field is constrained to vanish. While superluminal dispersion relations hardly affect the standard results, we find that subluminal dispersion relations can lead to relatively large modifications.
13913623
Hawking fluxes, back reaction and covariant anomalies
Starting from the chiral covariant effective action approach of Banerjee and Kulkarni (2008 Phys. Lett. B 659 827), we provide a derivation of the Hawking radiation from a charged black hole in the presence of gravitational back reaction. The modified expressions for charge and energy flux, due to the effect of one-loop back reaction are obtained.
15809457
Hawking radiation, effective actions and covariant boundary conditions
From an appropriate expression for the effective action, the Hawking radiation from charged black holes is derived, using only covariant boundary conditions at the event horizon. The connection of our approach with the Unruh vacuum and the recent analysis [S.P. Robinson, F. Wilczek, Phys. Rev. Lett. 95 (2005) 011303, gr-qc/0502074; S. Iso, H. Umetsu, F. Wilczek, Phys. Rev. Lett. 96 (2006) 151302, hep-th/0602146; R. Banerjee, S. Kulkarni, arXiv: 0707.2449 [hep-th]] of Hawking radiation using anomalies is established.
18639894
Nonconservation of energy-momentum tensor in classical Liouville theory
where Ah is the area of the horizon. In this context, the classical Liouville theory [4] has gained considerable importance owing to the work of Solodukhin [5]. He showed that the computation of the black hole entropy can be carried out at the classical level. He observed that the 4-dimensional Einstein-Hilbert action can be reduced to an effective 2-dimensional theory, with fixed boundary conditions on the horizon, by performing a dimensional reduction with the ansatz of spherical symmetry and writing the metric in conformally flat form. This action can then be transformed to a form similar to the classical Liouville theory which in turn admits a Virasoro algebra near the horizon with a nontrivial classical central charge. The computation of this central charge then allows to determine the black hole entropy from the Cardy formula [6]. This approach was then used to study thermodynamic properties of black hole with a bifurcate killing horizon [7]. However, it is a well known fact from general field theoretic considerations [8, 9] that a central charge is related to diffeomorphism anomaly manifested as a nonconservation of the energy-momentum tensor. This relation is discussed from quantum considerations. The central charge and the diffeomorphism anomaly reveal different manifestations of the same phenomenon – a breakdown of classical symmetry upon the process of quantisation. Since the central charge is obtained [5, 7] in a classical Liouville theory, a natural question that arises is whether, in such a theory, there is a diffeomorphism anomaly. The principal objective of this paper is to show that this is indeed true. In this paper, we show explicitly that if we consider terms in the expansion of the metric, near the horizon, beyond leading order, then it leads to a diffeomorphism anomaly which is compatible with the fact that the theory has a nontrivial classical central charge. The computation of this anomaly has in fact been done to all orders. To begin with, we consider a four-dimensional spherically symmetric metric of the form
14909136
Remarks on the generalized Chaplygin gas
We develop an action formulation for the generalized Chaplygin gas (GCG). The most general form for the nonrelativistic GCG action is derived consistent with the equation of state. We also discuss a relativistic formulation for GCG by providing a detailed analysis of the Poincare algebra.
119219379
On the On-Shell Renormalization of the Chargino and Neutralino Masses in the MSSM
We discuss the choice of input parameters for the renormalization of the chargino and neutralino sector in the minimal supersymmetric standard model (MSSM) in the on-shell scheme. We show that one should chose the masses of a bino-like, a wino-like and a higgsino-like state as inputs in order to avoid large corrections to the masses of the other eigenstates in this sector. We also show that schemes where the higgsino-like input state is a neutralino are more stable than those where the mass of the higgsino-like chargino is used as input. The most stable scheme uses the masses of the wino-like chargino as well as the masses of the bino- and higgsino-like neutralinos as inputs.
9275094
The Automated Palomar 60 Inch Telescope
We have converted the Palomar 60 inch (1.52 m) telescope from a classic night‐assistant‐operated telescope to a fully robotic facility. The automated system, which has been operational since 2004 September, is designed for moderately fast (t ≾ 3 minutes) and sustained (R ≾ mag) observations of gamma‐ray burst afterglows and other transient events. Routine queue‐scheduled observations can be interrupted in response to electronic notification of transient events. An automated pipeline reduces data in real time, which is then stored on a searchable Web‐based archive for ease of distribution. We describe here the design requirements, hardware and software upgrades, and lessons learned from roboticization. We present an overview of the current system performance as well as plans for future upgrades.
91177292
SModelS: a tool for interpreting simplified-model results from the LHC and its application to supersymmetry
We present a general procedure to decompose Beyond the Standard Model (BSM) collider signatures presenting a $$\mathbb {Z}_2$$Z2 symmetry into Simplified Model Spectrum (SMS) topologies. Our method provides a way to cast BSM predictions for the LHC in a model independent framework, which can be directly confronted with the relevant experimental constraints. Our concrete implementation currently focusses on supersymmetry searches with missing energy, for which a large variety of SMS results from ATLAS and CMS are available. As show-case examples we apply our procedure to two scans of the minimal supersymmetric standard model. We discuss how the SMS limits constrain various particle masses and which regions of parameter space remain unchallenged by the current SMS interpretations of the LHC results.
118910770
A High Angular Resolution Search for the Progenitor of the Type Ic Supernova 2004gt
We report the results of a high spatial resolution search for the progenitor of Type Ic supernova SN 2004gt, using the newly commissioned Keck laser guide star adaptive optics (LGSAO) system along with archival Hubble Space Telescope data. This is the deepest search yet performed for the progenitor of any Type Ib/c event in a wide wavelength range stretching from the far-UV to the near-IR. We determine that the progenitor of SN 2004gt was most likely less luminous than MV = -5.5 mag and MB = -6.5 mag. The massive stars exploding as hydrogen-deficient core-collapse supernovae should have lost their outer hydrogen envelopes prior to their explosion, either through winds—such stars are identified within our Galaxy as Wolf-Rayet (W-R) stars—or to a binary companion. The luminosity limits we set rule out more than half of the known Galactic W-R stars as possible progenitors of this event. In particular, they imply that a W-R progenitor should have been among the more evolved (highly stripped, less luminous) of these stars, a concrete constraint on its evolutionary state just prior to core collapse. The possibility of a less luminous, lower mass binary progenitor cannot be constrained. This study demonstrates the power of LGS observations in furthering our understanding of core collapse and the physics powering supernovae, gamma-ray bursts, and X-ray flashes.
16091479
The Host Galaxies of Swift Dark Gamma-ray Bursts: Observational Constraints on Highly Obscured and Very High Redshift GRBs
In this work, we present the first results of our imaging campaign at Keck Observatory to identify the host galaxies of "dark" gamma-ray bursts (GRBs), events with no detected optical afterglow or with detected optical flux significantly fainter than expected from the observed X-ray afterglow. We find that out of a uniform sample of 29 Swift bursts rapidly observed by the Palomar 60 inch telescope through 2008 March (14 of which we classify as dark), all events have either a detected optical afterglow, a probable optical host-galaxy detection, or both. Our results constrain the fraction of Swift GRBs coming from very high redshift (z>7), such as the recent GRB 090423, to between 0.2% and 7% at 80% confidence. In contrast, a significant fraction of the sample requires large extinction columns (host-frame A_V ≳ 1 mag, with several events showing A_V > 2-6 mag), identifying dust extinction as the dominant cause of the dark GRB phenomenon. We infer that a significant fraction of GRBs (and, by association, of high-mass star formation) occurs in highly obscured regions. However, the host galaxies of dark GRBs seem to have normal optical colors, suggesting that the source of obscuring dust is local to the vicinity of the GRB progenitor or highly unevenly distributed within the host galaxy.