Analytic treatment of the black-hole bomb (2009)
A bosonic field impinging on a rotating black hole can be amplified as it scatters off the hole, a phenomena known as superradiant scattering. If in addition the field has a non-zero rest mass then...
Black-hole quasinormal resonances: Wave analysis versus a geometric-optics approximation (2009)
It has long been known that null unstable geodesics are related to the characteristic modes of black holes-- the so called quasinormal resonances. The basic idea is to interpret the free oscillations...
From Thermodynamics to the Bound on Viscosity (2009)
We show that the generalized second law of thermodynamics may shed much light on the mysterious Kovtun-Son-Starinets (KSS) bound on the ratio of viscosity to entropy density. In particular, we obtain...
Gravitation, Thermodynamics, and the Bound on Viscosity (2009)
The anti-de Sitter/conformal field theory (AdS/CFT) correspondence implies that small perturbations of a black hole correspond to small deviations from thermodynamic equilibrium in a dual field...
How pure is the tail of gravitational collapse ? (2009)
Waves propagating in a curved spacetime develop tails. In particular, it is well established that the late-time dynamics of gravitational collapse is dominated by a power-law decaying tail of the...
Slow relaxation of rapidly rotating black holes (2008)
We study analytically the relaxation phase of perturbed, rapidly rotating black holes. In particular, we derive a simple formula for the fundamental quasinormal resonances of near-extremal Kerr black...
Quasinormal resonances of near-extremal Kerr-Newman black holes (2008)
We study analytically the fundamental resonances of near-extremal, slowly rotating Kerr-Newman black holes. We find a simple analytic expression for these black-hole quasinormal frequencies in terms...
Return of the quantum cosmic censor (2008)
The influential theorems of Hawking and Penrose demonstrate that spacetime singularities are ubiquitous features of general relativity, Einstein's theory of gravity. The utility of classical general...
Weak Cosmic Censorship: As Strong as Ever (2008)
Spacetime singularities that arise in gravitational collapse are always hidden inside of black holes. This is the essence of the weak cosmic censorship conjecture. The hypothesis, put forward by...
Lifetime of unstable hairy black holes (2008)
During the last two decades solutions of black holes with various types of "hair" have been discovered. Remarkably, it has been established that many of these hairy black holes are unstable-- under...
Bounds on the mass-to-radius ratio for non-compact field configurations (2007)
It is well known that a spherically symmetric compact star whose energy density decreases monotonically possesses an upper bound on its mass-to-radius ratio, $2M/R\leq 8/9$. However, field...
Einstein-Yang-Mills Solitons: The Role of Gravity (2007)
The canonical Bartnik-McKinnon solitons are regular solutions of the coupled Einstein-Yang-Mills system in which gravity may balance the repulsive nature of the Yang-Mills field. We examine the role...
We study analytically the initial value problem for a self-interacting (massive) scalar-field on a Reissner-Nordstrom spacetime. Following the no-hair theorem we examine the dynamical physical...
Late-Time Evolution of Charged Gravitational Collapse and Decay of Charged Scalar Hair - II (2007)
We study analytically the initial value problem for a charged massless scalarfield on a Reissner-Nordstrom spacetime. Using the technique of spectral decomposition we extend recent results on this...
We study the nonlinear gravitational collapse of a charged massless scalarfield. We confirm the existence of oscillatory inverse power-law tails along future timelike infinity, future null infinity...
We conjecture (analytically) and demonstrate (numerically) the existence of a fine-structure above the power-law behavior of the mass of black-holes that form in gravitational collapse of spherical...
Critical Behaviour and Universality in Gravitational Collapse of a Charged Scalar Field (2007)
We summarize results from a study of spherically symmetric collapse of a charged (complex) massless scalar-field [1]. We present an analytic argument which conjecture the generalization of the...
A note on the quantization of a multi-horizon black hole (2007)
We consider the quasinormal spectrum of a charged scalar field in the (charged) Reissner-Nordstrom spacetime, which has two horizons. The spectrum is characterized by two distinct families of...
Near-Extreme Black Holes and the Universal Relaxation Bound (2007)
A fundamental bound on the relaxation time \tau of a perturbed thermodynamical system has recently been derived, \tau \geq \hbar/\pi T, where $T$ is the system's temperature. We demonstrate...
Analytic Study of Rotating Black-Hole Quasinormal Modes (2007)
A Bohr-Sommerfeld equation is derived for the highly-damped quasinormal mode frequencies omega(n>>1) of rotating black holes. It may be written as 2\int_C(p_r+ip_0)dr=(n+1/2)h, where p_r is the...
Universal Bound on Dynamical Relaxation Times and Black-Hole Quasinormal Ringing (2006)
From information theory and thermodynamic considerations a universal bound on the relaxation time $\tau$ of a perturbed system is inferred, $\tau \geq \hbar/\pi T$, where $T$ is the system's...
Fermionic Quasinormal Spectrum of the Kerr Black Hole (2005)
We study {\it analytically} the asymptotic quasinormal spectrum of fermionic fields in the Kerr spacetime. We find an analytic expression for these black-hole resonances in terms of the black-hole...
Quasinormal Spectrum and Quantization of Charged Black Holes (2005)
Black-hole quasinormal modes have been the subject of much recent attention, with the hope that these oscillation frequencies may shed some light on the elusive theory of quantum gravity. We study...
Unruh radiation: from black holes to elementary particles (2005)
We advocate the idea that Unruh's quantum radiation, whose theoretical discovery was originally motivated by the physics of black holes, may have important implications on the structure and dynamics...
Selection Rules for Black-Hole Quantum Transitions (2005)
We suggest that quantum transitions of black holes comply with selection rules, analogous to those of atomic spectroscopy. In order to identify such rules, we apply Bohr's correspondence principle to...
Survival Probabilities of History-Dependent Random Walks (2005)
We analyze the dynamics of random walks with long-term memory (binary chains with long-range correlations) in the presence of an absorbing boundary. An analytically solvable model is presented, in...
Intermediate Asymptotics of the Kerr Quasinormal Spectrum (2005)
We study analytically the quasinormal mode spectrum of near-extremal (rotating) Kerr black holes. We find an analytic expression for these black-hole resonances in terms of the black-hole physical...
High-Order Corrections to the Entropy and Area of Quantum Black Holes (2004)
The celebrated area-entropy formula for black holes has provided the most important clue in the search for the elusive theory of quantum gravity. We explore the possibility that the (linear)...
Survival probabilities in time-dependent random walks (2004)
We analyze the dynamics of random walks in which the jumping probabilities are periodic {\it time-dependent} functions. In particular, we determine the survival probability of biased walkers who are...
Evolutionary Minority Game: The Roles of Response Time and Mutation Threshold (2004)
In the evolutionary minority game, agents are allowed to evolve their strategies (``mutate'') based on past experience. We explore the dependence of the system's global behavior on the response time...
Phase-Transition in Binary Sequences with Long-Range Correlations (2003)
Motivated by novel results in the theory of correlated sequences, we analyze the dynamics of random walks with long-term memory (binary chains with long-range correlations). In our model, the...
Asymptotic quasinormal mode spectrum of rotating black holes (2003)
Motivated by novel results in the theory of black-hole quantization, we study {\it analytically} the quasinormal modes (QNM) of ({\it rotating}) Kerr black holes. The black-hole oscillation...
Strategy updating rules and strategy distributions in dynamical multiagent systems (2003)
In the evolutionary version of the minority game, agents update their strategies (gene-value $p$) in order to improve their performance. Motivated by recent intriguing results obtained for...
Kerr black hole quasinormal frequencies (2003)
Black-hole quasinormal modes (QNM) have been the subject of much recent attention, with the hope that these oscillation frequencies may shed some light on the elusive theory of quantum gravity. We...
Time-Dependent Random Walks and the Theory of Complex Adaptive Systems (2002)
Motivated by novel results in the theory of complex adaptive systems, we analyze the dynamics of random walks in which the jumping probabilities are {\it time-dependent}. We determine the survival...
Temporal oscillations and phase transitions in the evolutionary minority game (2002)
The study of societies of adaptive agents seeking minority status is an active area of research. Recently, it has been demonstrated that such systems display an intriguing phase-transition: agents...
Cosmic Censorship, Area Theorem, and Self-Energy of Particles (2002)
The (zeroth-order) energy of a particle in the background of a black hole is given by Carter's integrals. However, exact calculations of a particle's {\it self-energy} (first-order corrections) are...
Wave Tails in Time Dependent Backgrounds (2002)
It is well-known that waves propagating under the influence of a scattering potential develop ``tails''. However, the study of late-time tails has so far been restricted to time-independent...
Self-Segregation vs. Clustering in the Evolutionary Minority Game (2002)
Complex adaptive systems have been the subject of much recent attention. It is by now well-established that members (`agents') tend to self-segregate into opposing groups characterized by extreme...
Discrete Black-Hole Radiation and the Information Loss Paradox (2000)
Hawking's black hole information puzzle highlights the incompatibility between our present understanding of gravity and quantum physics. However, Hawking's prediction of black-hole evaporation is at...
Cosmic Censorship: The Role of Quantum Gravity (2000)
The cosmic censorship hypothesis introduced by Penrose thirty years ago is still one of the most important open questions in {\it classical} general relativity. In this essay we put forward the idea...
Wave Propagation in Nontrivial Backgrounds (2000)
It is well known that waves propagating in a nontrivial medium develop ``tails''. However, the exact form of the late-time tail has so far been determined only for a narrow class of models. We...
Black-hole radiation, the fundamental area unit, and the spectrum of particle species (2000)
Bekenstein and Mukhanov have put forward the idea that, in a quantum theory of gravity a black hole should have a discrete mass spectrum with a concomitant {\it discrete} line emission. We note that...
Evidence for a null entropy of extremal black holes (2000)
We present some arguments in support of a {\it zero} entropy for {\it extremal} black holes. These rely on a combination of both quantum, thermodynamic, and statistical physics arguments. This result...
Gravitation, the Quantum, and Bohr's Correspondence Principle (2000)
The black hole combines in some sense both the ``hydrogen atom'' and the ``black-body radiation'' problems of quantum gravity. This analogy suggests that black-hole quantization may be the key to a...
Cosmic Censorship: the Role of Quantum Physics (1999)
The cosmic censorship hypothesis introduced by Penrose thirty years ago is still one of the most important open questions in {\it classical} general relativity. The main goal of this paper is to put...
Radiative Tail of Realistic Rotating Gravitational Collapse (1999)
An astrophysically realistic model of wave dynamics in black-hole spacetimes must involve a non-spherical background geometry with angular momentum. We consider the evolution of gravitational (and...
High-Order Contamination in the Tail of Gravitational Collapse (1999)
It is well known that the late-time behaviour of gravitational collapse is {\it dominated} by an inverse power-law decaying tail. We calculate {\it higher-order corrections} to this power-law...
Black-Hole Polarization and Cosmic Censorship (1999)
The destruction of the black-hole event horizon is ruled out by both cosmic censorship and the generalized second law of thermodynamics. We test the consistency of this prediction in a (more)...
The assimilation of a quantum (finite size) particle by a Reissner-Nordstr\"om black hole inevitably involves an increase in the black-hole surface area. It is shown that this increase can be...
Universal Upper Bound to the Entropy of a Charged System (1999)
We derive a universal upper bound to the entropy of a charged system. The entropy bound follows from application of the generalized second law of thermodynamics to a gedanken experiment in which an...
Improved Upper Bound to the Entropy of a Charged System (1999)
Recently, we derived an improved universal upper bound to the entropy of a charged system $S \leq \pi (2E b-q^2)/ \hbar$. There was, however, some uncertainty in the value of the numerical factor...
Mode-Coupling in Rotating Gravitational Collapse of a Scalar Field (1999)
We present an analytic study of the mode-coupling phenomena for a scalar field propagating on a rotating Kerr background. Physically, this phenomena is caused by the dragging of reference frames, due...
We consider the late-time evolution of {\it gravitational} and electromagnetic perturbations in realistic {\it rotating} Kerr spacetimes. We give a detailed analysis of the mode-coupling phenomena in...
The Inner Structure of Black Holes (1999)
We study the gravitational collapse of a self-gravitating charged scalar-field. Starting with a regular spacetime, we follow the evolution through the formation of an apparent horizon, a Cauchy...
Universal Entropy Bound for Rotating Systems (1999)
We conjecture a universal upper bound to the entropy of a rotating system. The entropy bound follows from application of the generalized second law of thermodynamics to an idealized gedanken...
Bohr's Correspondence Principle and The Area Spectrum of Quantum Black Holes (1998)
During the last twenty-five years evidence has been mounting that a black-hole surface area has a {\it discrete} spectrum. Moreover, it is widely believed that area eigenvalues are {\it uniformally}...
Late-Time Evolution of Realistic Rotating Collapse and The No-Hair Theorem (1998)
We study analytically the asymptotic late-time evolution of realistic rotating collapse. This is done by considering the asymptotic late-time solutions of Teukolsky's master equation, which governs...
Mass-Inflation in Dynamical Gravitational Collapse of a Charged Scalar-Field (1998)
We study the inner-structure of a charged black-hole which is formed from the gravitational collapse of a self-gravitating charged scalar-field. Starting with a regular spacetime, we follow the...
We study analytically the initial value problem for a self-interacting (massive) scalar-field on a Reissner-Nordstr\"om spacetime. Following the no-hair theorem we examine the dynamical physical...
We study the nonlinear gravitational collapse of a charged massless scalar-field. We confirm the existence of oscillatory inverse power-law tails along future timelike infinity, future null infinity...
Late-Time Evolution of Charged Gravitational Collapse and Decay of Charged Scalar Hair - II (1998)
We study analytically the initial value problem for a charged massless scalar-field on a Reissner-Nordstr\"om spacetime. Using the technique of spectral decomposition we extend recent results on this...
Late-Time Evolution of Charged Gravitational Collapse and Decay of Charged Scalar Hair - I (1997)
We study analytically the asymptotic evolution of charged fields around a Reissner-Nordstr\"om black-hole. Following the no-hair theorem we focus attention on the dynamical mechanism by which the...
Critical Behaviour and Universality in Gravitational Collapse of a Charged Scalar Field (1996)
We summarize results from a study of spherically symmetric collapse of a {\it charged} (complex) massless scalar-field \cite{Hod}. We present an analytic argument which conjecture the generalization...
Fine-Structure of Choptuik's Mass-Scaling Relation (1996)
We conjecture (analytically) and demonstrate (numerically) the existence of a fine-structure above the power-law behavior of the mass of black-holes that form in gravitational collapse of spherical...