Papers by Marcelo Schiffer
Physical Review D, 1990
Unruh's mixed state of a field with a zero-frequency mode, which purportedly contributes an a... more Unruh's mixed state of a field with a zero-frequency mode, which purportedly contributes an arbitrarily large entropy for a given energy, is actually a mixture of pure states belonging to different systems, since the mean value of the scalar field is different for each pure state in the mixture. Considerations related to superfluidity support the idea that vanishing entropy is to be ascribed to a zero-frequency mode.
Physical Review Letters, 1994
General Relativity and Gravitation, 1995
In this essay we compare the response of a black hole to incoming radiation to that one of a syst... more In this essay we compare the response of a black hole to incoming radiation to that one of a system consisting of a hot source hidden behind a semi-transparent mirror, and the two happen to agree. Then, we display a thermodynamical proof showing that this agreement is not incidental: it is a universal feature of an ideal grey body. As a by-product of this argument the universality of superradiance emerges: absorptive media in rotation, instead of damping incoming radiation, are responsible for its amplification for all superradiant modes. Our main conclusion here is that the black hole response to incoming radiation and superandiance are not features that arise because black holes are “exceptional” systems but, on the contrary, because they are very “ordinary” in the sense that they fall into the category of ideal grey bodies.
Modern Physics Letters A, 1991
The entropy bound from black hole thermodynamics can be invoked to set limits for temperatures at... more The entropy bound from black hole thermodynamics can be invoked to set limits for temperatures at which hadrons can survive as a confined system. We find that this implies that the pion can be formed in heavy ion collisions, much later than heavier mesons, for example the ρ-meson, when the fireball is cooler. The temperature found in a simple model agree qualitatively with experiment. We also suggest that this may be the reason why in pion interferometry experiments the space-time volume of the pion source seems large.
Physical Review D, 1989
The quantum bound on specific entropy for free fields states that the ratio of entropy S to total... more The quantum bound on specific entropy for free fields states that the ratio of entropy S to total energy E of a system with linear dimension R cannot be larger than 2~R /Ac. Here we prove this bound for a generic system consisting of a noninteracting quantum field in three space dimensions confined to a cavity of arbitrary shape and topology. S(E) is defined as the logarithm of the number of quantum states (including the vacuum) accessible up to energy E. An integral equation is derived which relates an upper bound on S(E) to the one-particle energy spectrum in the given cavity. The spectrum may always be bounded from above by a power law in energy whose proportionality constant is the g function for the spectrum of the cavity. This last is not calculable in the generic case, but it is here proven to be bounded by that for a sphere which circumscribes the actual cavity. Thus the one-particle spectrum for all cavities that fit inside a given sphere is bounded by a generic formula which can be computed given the field. With the help of this result the integral equation is solved for a fictitious system whose entropy must bound that of the actual system. The resulting bound on S(E)/E proves to be smaller than 2~R/Ac with R interpreted as the radius of the enveloping sphere.
Speculation that the fine-structure constant α varies in spacetime has a long history. We derive,... more Speculation that the fine-structure constant α varies in spacetime has a long history. We derive, in 4-D general relativity and in isotropic coordinates, the solution for a charged spherical black hole according to the framework for dynamical α (Bekenstein 1982). This solution coincides with a previously known one-parameter extension of the dilatonic black hole family. Among the notable properties of varying-α charged black holes are adherence to a "no hair" principle, the absence of the inner (Cauchy) horizon of the Reissner-Nordstrom black holes, the nonexistence of precisely extremal black holes, and the appearance of naked singularities in an analytic extension of the relevant metric. The exteriors of almost extremal electrically (magnetically) charged black holes have simple structures which makes their influence on applied magnetic (electric) fields transparent. We re-derive the thermodynamic functions of the modified black holes; the otherwise difficult calculation ...
In this essay we show that an uncharged black-hole moving superluminally in a transparent dielect... more In this essay we show that an uncharged black-hole moving superluminally in a transparent dielectric medium violates Hawking's area theorem. The violation is overcome through the emission of radiation. Since modes cannot emerge from the black hole itself, this radiation must originate from a collective effect in the medium, in complete analogy with the Vavilov-Cherenkov effect. However, because the black-hole is uncharged, the emission mechanism must be different. We discuss the physical origin of the effect and obtain a Newtonian estimative. Then we obtain the appropriate equations in the relativistic case and show that the field which is radiated away is a combination of gravitational and electromagnetic degrees of freedom. Possible astrophysical relevance for the detection of primordial black-holes and binary systems is discussed.
In this paper we calculate charge fluctuations of a Schwarzschild black-hole of mass M in thermal... more In this paper we calculate charge fluctuations of a Schwarzschild black-hole of mass M in thermal equilibrium with radiation and an electron-positron plasma confined within a vessel of radius R. We show that charge fluctuations are always present, even if the black-hole is neutral and the overall charge of the system vanishes. Furthermore, if R/M >>1 the system becomes unstable under charge fluctuations. Surprisingly enough, besides the expected thermodynamical black hole charge fluctuation that result from the fluctuations on the number of charge carriers, there are other contributions to the overall charge fluctuation of the black-hole which, against our intuition, do not depend upon the charge of the particles. We conjecture that one of the contributions is an intrinsic purely quantum mechanical fluctuation of the black-hole itself as it does not depend on any of the control parameters, namely the radius of the confining cavity nor the temperature of the system, and even no...
The purpose of this paper is to show that as a matter of principle, it is not appropriate to cons... more The purpose of this paper is to show that as a matter of principle, it is not appropriate to consider Schwarzschild black holes in thermal equilibrium with radiation because, even spinless and neutral holes undergo fluctuations of charge and angular momentum. Therefore, there will be a spread of these quantities around their zeromean values. We calculate these spreads for a black hole in thermal contact with charged scalar particles and show that angular momentum fluctuations are governed by the size of the cavity, larger cavities yielding larger angular momentum fluctuations. This behaviour is expected if black hole angular momentum fluctuations stem from the random absorption and emission of quanta with random angular momenta from the thermal bath. Furthermore, in the limit R/2M ≫ 1 charge fluctuations ∆Q 2 /(ch) ∼ 1/(4π), that is to say, they become scale independent. This is expected if the underlying physics of these fluctuations is the random absorption and emission of charged quanta from the thermal bath. The independence of these fluctuations upon the elementary charge of the field is puzzling because it tells us that either the scale of the elementary charge is fixed by black hole physics to be α ∼ 1/4π (this gives an elementary charge which is only three times the charge of the electron), or the underlying physical process responsible these fluctuations is not known and remains to be cleared up.
Inertial motion superradiance, the emission of radiation by an initially unexcited system moving ... more Inertial motion superradiance, the emission of radiation by an initially unexcited system moving inertially but superluminally through a medium, has long been known. Rotational superradiance, the amplification of radiation by a rotating rigid object, was recognized much later, principally in connection with black hole radiances. Here we review the principles of inertial motion superradiance and prove thermodynamically that the Ginzburg–Frank condition for superradiance coincides with the condition for superradiant amplification of already existing radiation. Examples we cite include a new type of black hole superradiance. We correct Zel’dovich’s thermodynamic derivation of the Zel’dovich–Misner condition for rotational superradiance by including the radiant entropy in the bookkeeping. We work out in full detail the electrodynamics of the Zel’dovich rotating cylinder, including a general electrodynamic proof of the Zel’dovich–Misner condition, and explicit calculations of the superra...
In this paper we put forward a mechanism in which imploding shock waves emit electromagnetic radi... more In this paper we put forward a mechanism in which imploding shock waves emit electromagnetic radiation in the spectral region λ0 ∼ = 2πR0., where R0 is the radius of the shock by the time it is first formed. The mechanism relies on three different pieces of Physics: Maxwell’s equations, the existence of corrugation instabilities of imploding shock waves and, last but not least, the Inertial Polarization Principle. The principle is extensively discussed: how it emerges from very elementary physics and finds experimental support in shock waves propagating in water. The spectrum of the emitted light is obtained and depends upon two free parameters, the amplitude of the instabilities and the cut-off Rmax, the shocks ’ spatial extension. The spectral intensity is determined by the former, but its shape turns out to have only a mild dependence on the latter, in the region of physical interest. The matching with the observed spectrum requires a fine tuning of the perturbation amplitude ε ∼...
Apesar de o Universo hoje ser bastante homogeneo em grandes escalas, em pequenas escalas ele e ba... more Apesar de o Universo hoje ser bastante homogeneo em grandes escalas, em pequenas escalas ele e bastante inomogeneo. No contexto do Modelo Padrao , as inomogeneidades so podem evoluir logo apos a recombinacao e a densidade cresce em forma de potencia do tempo. Recentemente tem sido proposta [2] uma variacao da teoria da Relatividade Geral, na qual as interacoes gravitacionais sao mediadas atraves de uma metrica e um campo escalar complexo. Essa nova teoria, conhecida como Phase Coupled Gravity (PCG) tem o proposito de explicar as curvas de rotacao planas de galaxias sem a necessidade de postular consideravel quantidade de materia escura permeando o Universo. Nessa tese mostramos que numa das versoes da teoria PCG, envolvendo um potencial quadratico, durante uma fase de expansao inflacionaria ocorre um crescimento de forma aproximadamente exponencial da densidade contraste. Consequencias sao discutidas Abstract
arXiv: General Relativity and Quantum Cosmology, 2016
In this paper we calculate charge fluctuations of a Schwarzschild black-hole of mass $M$ confined... more In this paper we calculate charge fluctuations of a Schwarzschild black-hole of mass $M$ confined within a perfectly reflecting cavity of radius R in thermal equilibrium with various species of radiation and fermions . Charge conservation is constrained by a Lagrange multiplier (the chemical potential). Black hole charge fluctuations are expected owing to continuous absorption and emission of particles by the black hole. For black holes much more massive than $10^{16} g$ , these fluctuations are exponentially suppressed. For black holes lighter than this, the Schwarzschild black hole is unstable under charge fluctuations for almost every possible size of the confining vessel. The stability regime and the fluctuations are calculated through the second derivative of the entropy with respect to the charge. The expression obtained contains many puzzling terms besides the expected thermodynamical fluctuations: terms corresponding to instabilities that do not depend on the specific value ...
arXiv: General Relativity and Quantum Cosmology, 2020
We discuss the possibility that gravitational waves are trapped in space by gravitational interac... more We discuss the possibility that gravitational waves are trapped in space by gravitational interactions in 2-dimensional Jackiw-Teitelboim gravity. In the standard geon (gravitational electromagnetic entity) approach, the active region is introduced to confine gravitational waves spatially. In our approach, however, spacetime dependent traceless metric perturbations, i.e. "gravitational waves" are trapped by the vacuum geometry and can be stable against the backreaction due to the metric fluctuations. We expect that our approach may shed light on finding similar self-trapping solutions in 4-dimensional gravity.
We calculate the black hole mass distribution function that follows from the random emission of q... more We calculate the black hole mass distribution function that follows from the random emission of quanta by Hawking radiation and with this function we calculate the black hole mass fluctuation. From a complete different perspective we regard the black hole as quantum mechanical system with a quantized event horizon area and transition probabilities among the various energy levels and then calculate the mass dispersion. It turns out that there is a perfect agreement between the statistical and the microscopic calculations if and only if the area spectrum is linear. Accordingly, the quantum mechanical properties of the black hole which are supposedly relevant only at Planckian scales do leave an imprint in the black hole mass dispersion at much larger scales where gravity can be dealt classically, as one would expect from the correspondence principle.
In this paper we calculate charge fluctuations of a Schwarzschild black-hole of mass $M$ in therm... more In this paper we calculate charge fluctuations of a Schwarzschild black-hole of mass $M$ in thermal equilibrium with radiation and an electron-positron plasma confined within a vessel of radius R. We show that charge fluctuations are always present, even if the black-hole is neutral and the overall charge of the system vanishes. Furthermore, if $ R/M >>1 $ the system becomes unstable under charge fluctuations. Surprisingly enough, besides the expected thermodynamical black hole charge fluctuation that result from the fluctuations on the number of charge carriers, there are other contributions to the overall charge fluctuation of the black-hole which, against our intuition, do not depend upon the charge of the particles. We conjecture that one of the contributions is an intrinsic purely quantum mechanical fluctuation of the black-hole itself as it does not depend on any of the control parameters, namely the radius of the confining cavity nor the temperature of the system, and e...
arXiv: General Relativity and Quantum Cosmology, 2020
In the early days of Black Hole Thermodynamics, Bekenstein calculated the statistical mass disper... more In the early days of Black Hole Thermodynamics, Bekenstein calculated the statistical mass dispersion of a macroscopic black hole under the assumption that this dispersion is a result of the random emission of quanta . His calculation led to a black hole squared mass dispersion that becomes negative for massive black holes. He named it {\it the mass width paradox}. Here we revisit the calculation on an axiomatic approach: we start with a set of postulates, and we do not assume a Gaussian distribution and the related approximations considered in the original paper and we reach similar conclusions. We argue that the paradox results from considering a black hole as a classical system, without an inner quantum structure: {\it a structureless black hole is not consistent with statistical physics.} . Assuming black hole area quantization and identical probability transition between neighbour quantum states we obtain the black hole probability of being in some area eigenstate. On the way, ...
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Papers by Marcelo Schiffer