arXiv subjects

S. Hamid Mehdipour

Publications and source records attributed to S. Hamid Mehdipour.

At least 19 recordsLinked to original sources

arXiv2019

Emergent GUP from Modified Hawking Radiation in Einstein-NED Theory

We present a general procedure for constructing exact black hole (BH) solutions with the magnetic charge in the context of nonlinear electrodynamics (NED) theory as well as in the coherent state approach to noncommutative geometry (NCG). In this framework, the Lagrangian density for the noncommutative Hayward BH is obtained and the weak energy condition (WEC) is satisfied. The noncommutative Hayward solution depends on two kind of charges which for the vanishing of them yields the Schwarzschild solution. Moreover, in order to find a link between the BH evaporation and uncertainty relations, we may calculate the Hawking temperature and find the effect of the Lagrangian density of BHs on the Hawking radiation. Therefore, a generalized uncertainty principle (GUP) emerges from the modified Hawking temperature in Einstein-NED theory. The origin of this GUP is the combined influence of a nonlinear magnetic source and an intrinsic property of the manifold associated with a fictitious charge. Finally, we find that there is an upper bound on the Lagrangian uncertainty of the BHs which are sourced by the NED field and/or the fictitious charge.

physics.gen-ph↗

arXiv2016

A comparison of remnants in noncommutative Bardeen black holes

We derive the mass term of the Bardeen metric in the presence of a noncommutative geometry induced minimal length. In this setup, the proposal of a stable black hole remnant as a candidate to store information is confirmed. We consider the possibility of having an extremal configuration with one degenerate event horizon and compare different sizes of black hole remnants. As a result, once the magnetic charge $g$ of the noncommutative Bardeen solution becomes larger, both the minimal nonzero mass $M_0$ and the minimal nonzero horizon radius $r_0$ get larger. This means, subsequently, under the condition of an adequate amount of $g$, the three parameters $g$, $M_0$, and $r_0$ are in a connection with each other linearly. According to our results, a noncommutative Bardeen black hole is colder than the noncommutative Schwarzschild black hole and its remnant is bigger, so the minimum required energy for the formation of such a black hole at particle colliders will be larger. We also find a closely similar result for the Hayward solution.

physics.gen-ph↗

arXiv2016

Entropic force law in the presence of a noncommutative inspired spacetime for a solar system scale

We first study some aspects of a physically inspired kind of a noncommutative spherically symmetric spacetime based on the Gaussian-smeared mass distribution for a solar system scale. This leads to the elimination of a singularity appeared in the origin of the spacetime. Afterwards, we investigate some features of Verlinde's scenario in the presence of the mentioned spacetime and derive several quantities such as Unruh-Verlinde temperature, the energy and the entropic force on three different types of holographic screens, namely the static, the stretched horizon and the accelerating surface.

physics.gen-ph↗

arXiv2014

Thermodynamical features of Verlinde's approach for a non-commutative Schwarzschild-anti-deSitter black hole in a broad range of scales

We try to study the thermodynamical features of a non-commutative inspired Schwarzschild-anti-deSitter black hole in the context of entropic gravity model, particularly for the model that is employed in a broad range of scales, from the short distances to the large distances. At small length scales, the Newtonian force is failed because one finds a linear relation between the entropic force and the distance. In addition, there are some deviations from the standard Newtonian gravity at large length scales.

physics.gen-ph↗

arXiv2014

Entropic gravity versus gravitational pseudotensors in static spherically symmetric spacetimes

We present some well-known energy-momentum complexes and evaluate the gravitational energy associated with static spherically symmetric spacetimes. In fact, the energy distribution of the aforementioned gravitational background that is contained in a two-sphere of radius $r$ shows that a test particle situated at a finite distance $r$ experiences the gravitational field of the effective gravitational mass. In addition, we apply Verlinde's entropic gravity to find the emergent gravitational energy on static spherically symmetric screens. In this setup, we find that the energy distribution in the prescription of Møller is similar to the energy derived from the emergent gravity, while other prescriptions give the different results. This result may confirm the argument of Lessner who argues that Møller's definition of energy is a powerful concept of energy in General Relativity.

physics.gen-ph↗

arXiv2013

Some aspects of entropic gravity in the presence of a noncommutative Schwarzschild-deSitter black hole

We study some features of entropic force approach in the presence of a noncommutative Schwarzschild-deSitter black hole. In this setup, there exists a similarity between the small and large scales. There are two finite cut-off in very short and long distances wherein the force and energy graph stop abruptly at those scales. We find that the existence of a deSitter core around the origin, induced by noncommutativity, in addition to a standard deSitter background at large scale may lead to a violation of the equivalence principle. Finally in order to directly observe the finite cut-off at short-scale gravity, caused by noncommutativity quantum fluctuations, we derive an effective gravitational constant.

physics.gen-ph↗

arXiv2012

Gravitational energy of a noncommutative Vaidya black hole

In this paper we evaluate the components of the energy-momentum pseudotensors of Landau and Lifshitz for the noncommutative Vaidya spacetime. The effective gravitational mass experienced by a neutral test particle present at any finite distance in the gravitational field of the noncommutative Vaidya black hole is derived. Using the effective mass parameter one finds that the naked singularity is massless and this supports Seifert's conjecture.

gr-qc↗

arXiv2012

Entropic force approach to noncommutative Schwarzschild black holes signals a failure of current physical ideas

Recently, a new perspective of gravitational-thermodynamic duality as an entropic force arising from alterations in the information connected to the positions of material bodies is found. In this paper, we generalize some aspects of this model in the presence of noncommutative Schwarzschild black hole by applying the method of coordinate coherent states describing smeared structures. We implement two different distributions: (a) Gaussian and (b) Lorentzian. Both mass distributions prepare the similar quantitative aspects for the entropic force. Our study shows, the entropic force on the smallest fundamental unit of a holographic screen with radius $r_0$ vanishes. As a result, black hole remnants are unconditionally inert even gravitational interactions do not exist therein. So, a distinction between gravitational and inertial mass in the size of black hole remnant is observed, i.e. the failure of the principle of equivalence. In addition, if one considers the screen radius to be less than the radius of the smallest holographic surface at the Planckian regime, then one encounters some unusual dynamical features leading to gravitational repulsive force and negative energy. On the other hand, the significant distinction between the two distributions is conceived to occur around $r_0$, and that is worth of mentioning: at this regime either our analysis is not the proper one, or non-extensive statistics should be employed.

gr-qc↗

arXiv2012

Entropic force approach in a noncommutative charged black hole and the equivalence principle

Recently, Verlinde has suggested a novel model of duality between thermodynamics and gravity which leads to an emergent phenomenon for the origin of gravity and general relativity. In this paper, we investigate some features of this model in the presence of noncommutative charged black hole by performing the method of coordinate coherent states representing smeared structures. We derive several quantities, e.g. temperature, energy and entropic force. Our approach clearly exhibits that the entropic force on a smallest fundamental cell of holographic surface with radius $r_0$ is halted. Accordingly, we can conclude that the black hole remnants are absolutely inert without gravitational interactions. So, the equivalence principle of general relativity is contravened due to the fact that it is now possible to find a difference between the gravitational and inertial mass. In other words, the gravitational mass in the remnant size does not emit any gravitational field, therefore it is experienced to be zero, contrary to the inertial mass. This phenomenon illustrates a good example for a feasible experimental confirmation to the entropic picture of Newton's Second law in very short distances.

gr-qc↗

arXiv2012

Planck-scale nonthermal correlations in a noncommutative geometry inspired Vaidya black hole

Using the noncommutative geometry inspired Vaidya metric obtained in terms of coordinate coherent states and also utilizing the generalized uncertainty principle (GUP), we show that the nonthermal nature of the Hawking spectrum leads to Planck-scale nonthermal correlations between emitted modes of evaporation. Our analysis thus exhibits that owing to self-gravitational effects plus noncommutativity and GUP influences, information can emerge in the form of Planck-scale correlated emissions from the black hole.

gr-qc↗

arXiv2012

Some examples of different descriptions of energy-momentum density in the context of Bianchi IX cosmological model

Based on the Bianchi type IX metric, we calculate the energy and momentum density components of the gravitational field for the five different definitions of energy-momentum, namely, Tolman, Papapetrou, Landau-Lifshitz, Møller and Weinberg. The energy densities of Møller and Weinberg become zero for the spacetime under consideration. In the other prescriptions, i.e., Tolman, Papapetrou and Landau-Lifshitz complexes, we find different non-vanishing energy-momentum densities for the given spacetime, supporting the well-known argument in General Relativity that the different definitions may lead to different distributions even in the same spacetime background.

gr-qc↗

arXiv2010

Charged particles' tunneling from a noncommutative charged black hole

We apply the tunneling process of charged massive particles through the quantum horizon of a Reissner-Nordstrom black hole in a new noncommutative gravity scenario. In this model, the tunneling amplitude on account of noncommutativity influences in the context of coordinate coherent states is modified. Our calculation points out that the emission rate satisfies the first law of black hole thermodynamics and is consistent with an underlying unitary theory.

gr-qc↗

arXiv2010

Hawking radiation as tunneling from a Vaidya black hole in noncommutative gravity

In the context of a noncommutative model of coordinate coherent states, we present a Schwarzschild-like metric for a Vaidya solution instead of the standard Eddington-Finkelstein metric. This leads to the appearance of an exact $(t - r)$ dependent case of the metric. We analyze the resulting metric in three possible causal structures. In this setup, we find a zero remnant mass in the long-time limit, i.e. an instable black hole remnant. We also study the tunneling process across the quantum horizon of such a Vaidya black hole. The tunneling probability including the time-dependent part is obtained by using the tunneling method proposed by Parikh and Wilczek in terms of the noncommutative parameter $σ$. After that, we calculate the entropy associated to this noncommutative black hole solution. However the corrections are fundamentally trifling; one could respect this as a consequence of quantum inspection at the level of semiclassical quantum gravity.

gr-qc↗

arXiv2009

Noncommutative Inspired Reissner-Nordström Black Holes in Large Extra Dimensions

Recently, a new noncommutative geometry inspired solution of the coupled Einstein-Maxwell field equations including black holes in 4-dimension is found. In this paper, we generalize some aspects of this model to the Reissner-Nordström (RN) like geometries with large extra dimensions. We discuss Hawking radiation process based on noncommutative inspired solutions. In this framework, existence of black hole remnant and possibility of its detection in LHC are investigated.

hep-th↗

arXiv2009

Parikh-Wilczek Tunneling from Noncommutative Higher Dimensional Black Holes

We study tunneling of massless and massive particles through the smeared quantum horizon of the extra-dimensional Schwarzschild black holes. The emission rate of the particles' tunneling is modified by noncommutativity effects in a bulk spacetime of dimension $d$. The issues of information loss and possible correlations between emitted particles are discussed. We show that even by considering both noncommutativity and braneworld effects, there is no correlation between different modes of evaporation at least at late-time and within approximations used in the calculations. However, incorporation of quantum gravity effects such as modification of the standard dispersion relation or generalization of the Heisenberg uncertainty principle, leads to the correlation between emitted particles. Although time-evolution of these correlations is not trivial, a part of information coming out of the black hole can be preserved in these correlations. On the other hand, as a well-known result of spacetime noncommutativity, a part of information may be preserved in a stable black hole remnant.

hep-th↗

arXiv2008

Quantum Gravity and Recovery of Information in Black Hole Evaporation

The Generalized Uncertainty Principle (GUP), motivated by current alternatives of quantum gravity, produces significant modifications to the Hawking radiation and the final stage of black hole evaporation. We show that incorporation of the GUP into the quantum tunneling process (based on the null-geodesic method) causes correlations between the tunneling probability of different modes in the black hole radiation spectrum. In this manner, the quantum information becomes encrypted in the Hawking radiation, and information can be recovered as non-thermal GUP correlations between tunneling probabilities of different modes.

gr-qc↗

arXiv2008

Gravitational Uncertainty and Black Hole Remnants

Possible existence of black holes remnants provides a suitable candidates for dark matter. In this paper we study the possibility of existence for such remnants. We consider quantum gravitational induced corrections of black hole's entropy and temperature to investigate the possibility of such relics. Observational scheme for detection of these remnants and their cosmological constraints are discussed.

gr-qc↗

arXiv2008

Hawking Radiation as Quantum Tunneling from Noncommutative Schwarzschild Black Hole

We study tunneling process through quantum horizon of a Schwarzschild black hole in noncommutative spacetime. This is done by considering the effect of smearing of the particle mass as a Gaussian profile in flat spacetime. We show that even in this noncommutative setup there will be no correlation between the different modes of radiation which reflects the fact that information doesn't come out continuously during the evaporation process at least at late-time. However, due to spacetime noncommutativity, information might be preserved by a stable black hole remnant.

gr-qc↗