The co-varying physical couplings (CPC) framework states that physical parameters like the speed of light in vacuum c, the Newtonian constant G, and the cosmological constant Λ could indeed vary with the spacetime coordinates x µ. Here,...
moreThe co-varying physical couplings (CPC) framework states that physical parameters like the speed of light in vacuum c, the Newtonian constant G, and the cosmological constant Λ could indeed vary with the spacetime coordinates x µ. Here, we assume a temporal variation, that is, c(t), G(t) and Λ(t). We show that the McVittie spacetime, a black hole in an expanding universe, is a solution of the CPC framework providing naturally an important parameter of the model. Then, we calculate the shadow angular radius of this black hole at cosmological distances. A black hole shadow in the CPC context could be either larger or smaller than the same shadow in the standard cosmology. It depends on how the set {c, G, Λ} varies with time or with the cosmic expansion.
There have been three geometrizations in history. The first one is historically due to the Pythagorean school and Plato, the second one comes from Galileo, Kepler, Descartes and Newton, and the third is Einstein's geometrization of...
moreThere have been three geometrizations in history. The first one is historically due to the Pythagorean school and Plato, the second one comes from Galileo, Kepler, Descartes and Newton, and the third is Einstein's geometrization of nature. The term geometrization of nature means the conception according to which nature (with its different meanings) is massively described by using geometry. In this article, I focus on the third geometrization, in which the black hole shadow phenomenon provides an interesting statement about the level of geometrization achieved by the theory of general relativity. With the black hole shadow described by the Einsteinian theory, the geometrical interpretation of nature relates shape to dynamics or, more specifically, the shadow silhouette to the angular momentum, regardless the matter content inside the black hole. As a consequence, spacetime symmetry could play the role of the formal cause in black hole physics.
Following a recent approach in which the gravitational field equations in curved spacetimes were presented in the Bopp–Podolsky electrodynamics, we obtained an approximate and spherically symmetric wormhole solution in this context. The...
moreFollowing a recent approach in which the gravitational field equations in curved spacetimes were presented in the Bopp–Podolsky electrodynamics, we obtained an approximate and spherically symmetric wormhole solution in this context. The calculations were carried out up to the linear approximation in both the spacetime geometry and the radial electric field. The solution presents a new parameter that comes from the Lagrangian of the model. Such a parameter was constrained by using the shadow radius of Sagittarius A*, recently revealed by the Event Horizon Telescope
Collaboration. Remarkably, the wormhole presented here is viable when its shadow is compared to the Sagittarius A* shadow.
Kasner cosmology is a vacuum and anisotropically expanding spacetime in the general relativity context. In this work, such a cosmological model is studied in another context, the bumblebee model, where the Lorentz symmetry is...
moreKasner cosmology is a vacuum and anisotropically expanding spacetime in the general relativity context. In this work, such a cosmological model is studied in another context, the bumblebee model, where the Lorentz symmetry is spontaneously broken. By using the bumblebee context it is possible to justify the anisotropic feature of the Kasner cosmology. Thus, the origin of the anisotropy in this cosmological model could be in the Lorentz symmetry breaking. Lastly, an application in the pre-inflationary cosmology is suggested.
The theory of regularity is a philosophical perspective in which laws of nature are just descriptions, that is to say, laws of nature do not govern the world. Moreover, according to the theory of regularity, the number of laws of nature...
moreThe theory of regularity is a philosophical perspective in which laws of nature are just descriptions, that is to say, laws of nature do not govern the world. Moreover, according to the theory of regularity, the number of laws of nature might be infinite, thus any attempt towards the theory of everything is doomed. Here I propose a special or restricted theory of regularity. The main difference as to the well-known version of that theory is both the range of validity and the scale of the laws of nature. Laws of
nature ought to be considered just inside the observable universe and within certain energy and length scales. Even so I apply the theory of regularity to the multiverse scenario. As a consequence, the special theory of regularity supports only two types of multiverses by comparison with our world: those ones with a different sequence of unique events and different laws of nature and those ones with the same sequence of unique events and the same laws of nature instanced by the unique events. The latter case is some sort of eternal recurrence or a parallel eternal recurrence.
An effect of the Lorentz symmetry breaking is pointed out in the cosmological context. Using a Bianchi I geometry coupled to the Kalb-Ramond field, a consequence of the Lorentz symmetry violation is indicated by a different rate of...
moreAn effect of the Lorentz symmetry breaking is pointed out in the cosmological context. Using a Bianchi I geometry coupled to the Kalb-Ramond field, a consequence of the Lorentz symmetry violation is indicated by a different rate of expansion in a given spatial direction. This article focuses on the coupling constant ξ1, which generates, from the Kalb-Ramond field, all three coefficients that give rise to the Lorentz violation in the gravity sector of the minimal Standard Model Extension. The coupling constant ξ1 increases the rate of expansion of the universe in a given direction during a dark energy era. As a consequence, a range of validity of that coupling constant is also obtained.
Nietzsche colocou-se como um antípoda a Platão. Mas em questões cosmológicas, o eterno retorno nietzschiano tem também alguns pontos em comum à cosmologia platônica descrita no Timeu. A finitude espacial, a ciclicidade cósmica e a ética...
moreNietzsche colocou-se como um antípoda a Platão. Mas em questões cosmológicas, o eterno retorno nietzschiano tem também alguns pontos em comum à cosmologia platônica descrita no Timeu. A finitude espacial, a ciclicidade cósmica e a ética cosmológica dizem respeito às semelhanças, já a infinitude temporal, a teleologia e a necessidade afastam os filósofos. Então, neste trabalho, aponto proximidades e afastamentos entre os dois filósofos em questões cosmológicas, além de sugerir alguma atualidade de suas concepções em relação à nossa ciência. Como veremos, a relação entre ética e cosmologia ainda se mostra atual.
Following a recent approach, complete and analytic solutions (brane and bulk) of regular black holes are shown in a brane context. The metrics are regular both on the four-dimensional brane and in the five-dimensional bulk. Like many...
moreFollowing a recent approach, complete and analytic solutions (brane and bulk) of regular black holes are shown in a brane context. The metrics are regular both on the four-dimensional brane and in the five-dimensional bulk. Like many brane world scenarios, the bulk spacetime is asymptotically anti-de Sitter. On the other hand, a de Sitter core on the brane avoids the singularity inside the event horizon, providing then well-known regular black holes on the brane. From the bulk perspective, the regular black holes are five-dimensional objects, with the event horizon extending to the extra dimension, but the de Sitter core is entirely on the four-dimensional brane.
In this work, a bumblebee field is adopted in order to generate cosmological anisotropies. For that purpose, we assume a Bianchi I cosmology, as the background geometry, and a bumblebee field coupled to it. Bumblebee models are examples...
moreIn this work, a bumblebee field is adopted in order to generate cosmological anisotropies. For that purpose, we assume a Bianchi I cosmology, as the background geometry, and a bumblebee field coupled to it. Bumblebee models are examples of a mechanism for the Lorentz symmetry violation by assuming a nonzero vacuum expectation value for the bumblebee field. When coupled to the Bianchi I geometry, which is not in agreement with a cosmological principle, the bumblebee field plays the role of a source of anisotropies and produces a preferred axis. Thus, a fraction of the cosmic anisotropies would come from the Lorentz symmetry violation. In the last part of the article, we try to assume an upper bound on the bumblebee field using the quadrupole and octopole moments of the cosmic microwave background radiation.
A mais comentada imagem científica em 2019 foi a imagem de M87*, buraco negro supermassivo central da galáxia Messier 87. A partir da observação da colaboração Event Horizon Telescope, fomos capazes de ver um buraco negro. Na verdade, a...
moreA mais comentada imagem científica em 2019 foi a imagem de M87*, buraco negro supermassivo central da galáxia Messier 87. A partir da observação da colaboração Event Horizon Telescope, fomos capazes de ver um buraco negro. Na verdade, a famosa imagem mostra-nos a sombra de M87*. Neste artigo, será introduzido o conceito de sombra de um buraco negro e indicada a sua importância para pesquisas nas áreas de gravitação e cosmologia.
In this work, we present black hole solutions with a cosmological constant in bumblebee gravity, which provides a mechanism for the Lorentz symmetry violation by assuming a nonzero vacuum expectation value for the bumblebee field. From...
moreIn this work, we present black hole solutions with a cosmological constant in bumblebee gravity, which provides a mechanism for the Lorentz symmetry violation by assuming a nonzero vacuum expectation value for the bumblebee field. From the gravitational point of view, such solutions are spherically symmetric black holes with an effective cosmological constant and are supported by an anisotropic energy-momentum tensor, conceived of as the manifestation of the bumblebee field in the spacetime geometry. Then we calculate the shadow angular radius for the proposed black hole solution with a positive effective cosmological constant. In particular, our results are the very first relation between the bumblebee field and the shadow angular size.
A constraint on the tidal charge generated within a brane world is shown. Using the shadow of a rotating black hole in a brane context in order to describe the M87* parameters recently announced by the Event Horizon Telescope...
moreA constraint on the tidal charge generated within a brane world is shown. Using the shadow of a rotating black hole in a brane context in order to describe the M87* parameters recently announced by the Event Horizon Telescope Collaboration, the deviation from circularity of the reported shadow produces an upper bound on the bulk's nonlocal effect, which is conceived of as a tidal charge in the four-dimensional brane induced by the five-dimensional bulk. Therefore, a deviation from circularity 10% leads to an upper bound on the tidal charge 0.004M 2 .
An upper bound on the parameter that provides a generalized uncertainty principle (GUP) is obtained from the black hole shadow. With the aid of a recent constraint between regular black holes and the GUP parameter, it is indicated a...
moreAn upper bound on the parameter that provides a generalized uncertainty principle (GUP) is obtained from the black hole shadow. With the aid of a recent constraint between regular black holes and the GUP parameter, it is indicated a relation between this parameter and the deviation from circularity of the black hole shadow. In the case of the recent announcement of the M87* results from the Event Horizon Telescope collaboration, a deviation from circularity $\lesssim 10\%$ imposes a GUP parameter $\beta_0 <10^{90}$.
We consider the stationary spherical accretion process of perfect fluids onto a class of spherically symmetric regular black holes corresponding to quantum-corrected Schwarzschild spacetimes. We show that the accretion rates can differ...
moreWe consider the stationary spherical accretion process of perfect fluids onto a class of spherically symmetric regular black holes corresponding to quantum-corrected Schwarzschild spacetimes. We show that the accretion rates can differ from the Schwarzschild case, suggesting that the de Sitter core inside these regular black holes, which indeed precludes the central singularity, can act for some cases as a sort of antigravitational source, decreasing the fluid's radial infall velocity in the accretion process, and for others as a gravitational enhancer, increasing the fluid flow into the black hole horizon. Our analysis and results can be extended and applied also to the problem of black hole evaporation in cosmological scenarios with phantom fluids. In particular, we show that the mass of typical regular black holes could be used to constrain turnaround events in cyclic cosmologies.
In spite of successful tests, the standard cosmological model, the ΛCDM model, possesses the most problematic concept: the initial singularity, also known as the big bang. In this paper—by adopting the Kantian difference between to think...
moreIn spite of successful tests, the standard cosmological model, the ΛCDM model, possesses the most problematic concept: the initial singularity, also known as the big bang. In this paper—by adopting the Kantian difference between to think of an object and to cognize an object—it is proposed a degree of scientificity using fuzzy sets. Thus, the notion of initial singularity will not be conceived of as a scientific issue because it does not belong to the fuzzy set of what is known. Indeed, the problematic concept of singularity is some sort of what Kant called the noumenon, but science, on the other hand, is constructed in the phenomenon. By applying the fuzzy degree of scientificity in cosmological models, one concludes that cosmologies with a contraction phase before the current expansion phase are potentially more scientific than the standard model. At the end of this article, it is shown that Kant's first antinomy of pure reason indicates a limit to our cosmological models.
It is shown that an aspect of the process of individuation may be thought of as a fuzzy set. The process of individuation has been interpreted as a two-valued problem in the history of philosophy. In this work, I intend to show that such...
moreIt is shown that an aspect of the process of individuation may be thought of as a fuzzy set. The process of individuation has been interpreted as a two-valued problem in the history of philosophy. In this work, I intend to show that such a process in its psychosocial aspect is better understood in terms of a fuzzy set, characterized by a continuum membership function. According to this perspective, species and their members present different degrees of individuation. Such degrees are measured from the membership function of the psychosocial process of individuation. Thus, a social analysis is suggested by using this approach in human societies.
It is shown that a notion of natural place is possible within modern physics. For Aristotle, the elements—the primary components of the world—follow to their natural places in the absence of forces. On the other hand, in general...
moreIt is shown that a notion of natural place is possible within modern physics. For Aristotle, the elements—the primary components of the world—follow to their natural places in the absence of forces. On the other hand, in general relativity, the so-called Carter-Penrose diagrams offer a notion of end for objects along the geodesics. Then, the notion of natural place in Aristotelian physics has an analog in the notion of conformal infinities in general relativity.
Bardeen regular black hole is commonly considered as a solution of general relativity coupled to a nonlinear electrodynamics. In this paper, it is shown that the Bardeen solution may be interpreted as a quantum-corrected Schwarzschild...
moreBardeen regular black hole is commonly considered as a solution of general relativity coupled to a nonlinear electrodynamics. In this paper, it is shown that the Bardeen solution may be interpreted as a quantum-corrected Schwarzschild black hole. This new interpretation is obtained by means of a generalized uncertainty principle applied to the Hawking temperature. Moreover, using the regular black hole of Bardeen, it is possible to evaluate the quantum gravity parameter of the generalized uncertainty principle or, assuming the recent upper bounds for such a parameter, to verify an enormous discrepancy between a cosmological constant and that measured by recent cosmological observations (∼ 10^120).
In this article, we present a study on thermodynamics of a class of regular black holes. Such a class includes Bardeen and Hayward regular black holes. We obtained thermodynamic quantities like Hawking temperature, entropy and heat...
moreIn this article, we present a study on thermodynamics of a class of regular black holes. Such a class includes Bardeen and Hayward regular black holes. We obtained thermodynamic quantities like Hawking temperature, entropy and heat capacity for the entire class. As part of an effort to indicate some physical observable to distinguish regular black holes from singular black holes, we suggest that regular black holes are colder than singular black holes. Besides, contrary to Schwarzschild black hole, that class of regular black holes may be thermodynamically stable. From a generalized uncertainty principle, we also obtained the quantum-corrected thermodynamics for the studied class. Such quantum corrections provide a logarithmic term for the quantum-corrected entropy.
In this work, we show that regular black holes in a Randall-Sundrum-type brane world model are generated by the nonlocal bulk influence, expressed by a constant parameter in the brane metric, only in the spherical case. In the axial case...
moreIn this work, we show that regular black holes in a Randall-Sundrum-type brane world model are generated by the nonlocal bulk influence, expressed by a constant parameter in the brane metric, only in the spherical case. In the axial case (black holes with rotation), this influence forbids them. A nonconstant bulk influence is necessary to generate regular black holes with rotation in this context.
Time machines are predictions of Einstein's theory of general relativity and provide a myriad of unsolved paradoxes. Convincing and general arguments against time machines and their paradoxes are missing in physics and philosophy so far....
moreTime machines are predictions of Einstein's theory of general relativity and provide a myriad of unsolved paradoxes. Convincing and general arguments against time machines and their paradoxes are missing in physics and philosophy so far. In this article, a philosophical argument against time machines is given. When thought of as a process, individuation refuses the idea of time machines, in particular travels into the past. With the aid of Nietzsche-Heraclitus' philosophy of becoming and Simondon's notion of process of individuation, I propose that time machines are modern fables, created by the man of ressentiment. In the amor fati formula of Nietzsche, I suggest the antipode to time machines.
One of the most important philosophers in history, the German Friedrich Nietzsche, is almost ignored by physicists. This author who declared the death of God in the 19th century was a science enthusiast, especially in the second period...
moreOne of the most important philosophers in history, the German Friedrich
Nietzsche, is almost ignored by physicists. This author who declared the death of God
in the 19th century was a science enthusiast, especially in the second period of his work.
With the aid of the physical concept of force, Nietzsche created his concept of will to
power. After thinking about energy conservation, the German philosopher had some
inspiration for creating his concept of eternal recurrence. In this article, some influences
of physics on Nietzsche are pointed out, and the topicality of his epistemological
position---the perspectivism---is discussed. Considering the concept of will to power, I
propose that the perspectivism leads to an interpretation where physics and science in
general are viewed as a game.
The ekpyrotic phase (a slow contraction cosmic phase before the current expansion phase) manages to solve the main problems of the standard cosmology by means of a scalar field interpreted as a cosmic fluid in the Friedmann equation....
moreThe ekpyrotic phase (a slow contraction cosmic phase before the current expansion phase) manages to solve the main problems of the standard cosmology by means of a scalar field interpreted as a cosmic fluid in the Friedmann equation. Moreover, this phase generates a nearly scale-invariant spectrum of perturbations in agreement with the latest data. Then, the ekpyrotic mechanism is a serious possibility to the inflationary model. In this work—by using the approach of deforming metrics at linear level—we point out that it is impossible to generate a black hole with spherical symmetry supported by an isotropic fluid in this cosmological scenario.
In this work we have deformed regular black holes which possess a general mass term described by a function which generalizes the Bardeen and Hayward mass functions. By using linear constraints in the energy-momentum tensor to generate...
moreIn this work we have deformed regular black holes which possess a general mass term described by a function which generalizes the Bardeen and Hayward mass functions. By using linear constraints in the energy-momentum tensor to generate metrics, the solutions presented in this work are either regular or singular. That is, within this approach, it is possible to generate regular or singular black holes from regular or singular black holes. Moreover, contrary to the Bardeen and Hayward regular solutions, the deformed regular black holes may violate the weak energy condition despite the presence of the spherical symmetry. Some comments on accretion of deformed black holes in cosmological scenarios are made.
Resumo: A recente observação das ondas gravitacionais corrobora uma das mais interessantes previsões da relatividade geral: os buracos negros. Pois as ondas gravitacionais detectadas pela colaboração LIGO ajustam-se muito bem dentro da...
moreResumo: A recente observação das ondas gravitacionais corrobora uma das mais interessantes previsões da relatividade geral: os buracos negros. Pois as ondas gravitacionais detectadas pela colaboração LIGO ajustam-se muito bem dentro da teoria da relatividade geral como um fenômeno produzido pela colisão de dois buracos negros. Sendo assim, a realidade física dos buracos negros parece ainda mais inegável hoje. Embora, uma mais contundente prova sobre a existência de buracos negros seria dada pela observação do seu horizonte de eventos, aquilo que o define. Neste artigo, é indicado que somente o horizonte de eventos define um buraco negro. Em sua definição, não há menção à singularidade em seu interior. Mostrar-se-á, assim, que buracos negros sem singularidade são possíveis. Tais são hoje chamados de buracos negros regulares. Abstract: The recent observation of gravitational waves confirms one of the most interesting predictions in general relativity: the black holes. Because the gravitational waves detected by LIGO fit very well within general relativity as a phenomenon produced by two colliding black holes. Then the reality of black holes seems almost undoubted today. However, a stronger proof on the reality of black holes would be indicated by the observation of the event horizon, which is what defines it. In this article, it is indicated that only the event horizon defines a black hole. There is no mention to the singularity in its definition. Thus, it will be shown that black holes without a singularity are possible. Such black holes are called regular black holes.
In "On the Heavens" Aristotle criticizes the Pythagorean point of view which claims the existence of a cosmic music and a cosmic sound. According to the Pythagorean argument, there exists a cosmic music produced by stars and planets....
moreIn "On the Heavens" Aristotle criticizes the Pythagorean point of view which claims the existence of a cosmic music and a cosmic sound. According to the Pythagorean argument, there exists a cosmic music produced by stars and planets. These celestial bodies generate sound in its movements, and the music appears due to the cosmic harmony. For Aristotle, there is no sound produced by celestial bodies. Then, there is no music as well. However, recently, LIGO (Laser Interferometer Gravitational-Waves Observatory) has detected the gravitational waves predicted by Einstein. In some sense, a sound originated from black holes has been heard. That is, Einstein or the General Relativity and LIGO appear to be with the Pythagoreanism and against the master of the Lyceum.
In this article, we present a bouncing cosmology inspired by a family of regular black holes. This scale-dependent cosmology deviates from the cosmological principle by means of a scale factor which depends on the time and the radial...
moreIn this article, we present a bouncing cosmology inspired by a family of regular black holes. This scale-dependent cosmology deviates from the cosmological principle by means of a scale factor which depends on the time and the radial coordinate as well. The model is isotropic but not perfectly homogeneous. That is, this cosmology describes a universe almost homogeneous only for large scales, such as our observable universe.
Neste trabalho, construímos novas soluções com simetria esférica ou axial para as equações do campo gravitacional induzido num cenário brana do tipo Randall-Sundrum, onde uma 3-brana com constante cosmológica está imersa num espaço-tempo...
moreNeste trabalho, construímos novas soluções com simetria esférica ou axial para as equações do campo gravitacional induzido num cenário brana do tipo Randall-Sundrum, onde uma 3-brana com constante cosmológica está imersa num espaço-tempo 5-dimensional conhecido como bulk. Para o caso esfericamente simétrico, com constante cosmológica negativa, obtivemos uma família de soluções numa brana assintoticamente anti-de Sitter, sendo que cada membro desta é diferenciado de outro por uma constante integração C, que fixada proveu-nos soluções de buracos negros ou buracos de minhocas. Com a mesma simetria, geometrias que descrevem buracos de minhoca foram encontradas numa brana assintoticamente de Sitter. Para o caso axialmente simétrico, métricas assintoticamente anti-de Sitter e de Sitter foram construídas no contexto citado. Propriedades óticas, como a rotação do vetor de polarização, foram estudadas, mostrando-nos algumas diferenças entre os mundos brana, tratados como uma teoria de gravitação modificada, e a relatividade geral.
In this work we have constructed axially symmetric vacuum solutions of the gravitational field equations in a Randall-Sundrum brane. A non-null effective cosmological constant is considered, and asymptotically de Sitter and anti-de Sitter...
moreIn this work we have constructed axially symmetric vacuum solutions of the gravitational field equations in a Randall-Sundrum brane. A non-null effective cosmological constant is considered, and asymptotically de Sitter and anti-de Sitter spacetimes are obtained. The solutions describe rotating black holes in a four-dimensional brane. Optical features of the solutions are treated, emphasizing the rotation of the polarization vector along null congruences.
Destaca-se na filosofia nietzschiana a importância do conceito de força proveniente da física para a construção de um dos seus principais conceitos: a vontade de potência. O conceito de força, que Nietzsche buscou na mecânica clássica,...
moreDestaca-se na filosofia nietzschiana a importância do conceito de força proveniente da física para a construção de um dos seus principais conceitos: a vontade de potência. O conceito de força, que Nietzsche buscou na mecânica clássica, quase desaparece na física do século XX com a teoria quântica de campos e a teoria da relatividade geral. Ainda é possível, na ciência de hoje, o mundo nietzschiano como forças em disputa, uma cosmologia dionisíaca?
Obtivemos famílias de soluções estáticas e esfericamente simétricas para buracos negros numa brana com vácuo, constante cosmológica não nula e imersa num bulk 5-dimensional assintoticamente anti-de Sitter. Para o caso das geometrias...
moreObtivemos famílias de soluções estáticas e esfericamente simétricas para buracos negros numa brana com vácuo, constante cosmológica não nula e imersa num bulk 5-dimensional assintoticamente anti-de Sitter. Para o caso das geometrias assintoticamente de Sitter, o único membro da família obtida foi a geometria Schwarzschild-de Sitter extrema. Para o caso de geometrias assintoticamente anti-de Sitter, obtivemos toda uma família de soluções, onde cada elemento desta família é determinado por uma constante C. Estudamos o comportamento destas soluções próximo e longe do horizonte de eventos. A seguir, analisamos a evolução de um campo escalar não massivo no exterior dos buracos negros obtidos. Verificamos analiticamente e numericamente o comportamento do potencial efetivo em função da coordenada tartaruga próximo ao horizonte de eventos. Para qualquer geometria ou solução desta família observamos que o campo escalar não massivo decai com o tempo, e o tipo de decaimento depende do valor da constante C. Assim, toda a família de soluções obtida mostrou-se estável.
We revisit here a recent work on regular rotating black holes. We introduce a new mass function generalizing the commonly used Bardeen and Hayward mass functions and extend the recently proposed solutions in order to accommodate a...
moreWe revisit here a recent work on regular rotating black holes. We introduce a new mass function generalizing the commonly used Bardeen and Hayward mass functions and extend the recently proposed solutions in order to accommodate a cosmological constant Λ. We discuss some aspects of the causal structure (horizons) and the ergospheres of the new proposed solutions. We also show that, in contrast with the spherically symmetrical case, the black hole rotation will unavoidably lead to the violation of the weak energy condition for any physically reasonable choice of the mass function, reinforcing the idea the description of the interior region of a Kerr black hole is much more challenging than in the Schwarzschild case.
Neste trabalho, realizamos uma aproximação entre as cosmologias científicas não singulares (sem a singularidade inicial, o big bang), especialmente os modelos cíclicos, e o pensamento do eterno retorno de Nietzsche. Além disso, sugerimos...
moreNeste trabalho, realizamos uma aproximação entre as cosmologias científicas não singulares (sem a singularidade inicial, o big bang), especialmente os modelos cíclicos, e o pensamento do eterno retorno de Nietzsche. Além disso, sugerimos respostas para o porquê da busca por "provas" científicas do eterno retorno feita pelo filósofo na década de 1880.
In this work we have derived a class of geometries which describe black holes and wormholes in Randall-Sundrum-type brane models, focusing mainly on asymptotically anti-de Sitter backgrounds. We show that by continuously deforming the...
moreIn this work we have derived a class of geometries which describe black holes and wormholes in Randall-Sundrum-type brane models, focusing mainly on asymptotically anti-de Sitter backgrounds. We show that by continuously deforming the usual four dimensional vacuum background, a specific family of solutions is obtained. Maximal extensions of the solutions are presented, and their causal structures are discussed.
In this work we present a class of geometries which describes wormholes in a Randall-Sundrum brane model, focusing on de Sitter backgrounds. Maximal extensions of the solutions are constructed and their causal structures are discussed. A...
moreIn this work we present a class of geometries which describes wormholes in a Randall-Sundrum brane model, focusing on de Sitter backgrounds. Maximal extensions of the solutions are constructed and their causal structures are discussed. A perturbative analysis is developed, where matter and gravitational perturbations are studied. Analytical results for the quasinormal spectra are obtained and an extensive numerical survey is conducted. Our results indicate that the wormhole geometries presented are stable.