Modern Physics Letters A

In this paper, we discuss remnants of the Bardeen regular black hole motivated by using the concept of thermal fluctuations. First, we derive the equilibrium values of various thermodynamic quantities like entropy, Hawking temperature, pressure, internal energy, Helmholtz free energy and Gibbs free energy in the non-extended phase space. We then discuss geometrothermodynamics (GTD) of Bardeen black hole to study its stability. Next, we estimate the size of black hole remnant in terms of some known parameters of the black hole solution. Motivated by the fact that estimation of size, characteristics and stability of remnants of black holes could further increase our understanding of binary collisions, information loss paradox and dark energy, the black hole remnant, which gives an idea about stable mass left over after evaporation of black hole, is seen to owe its presence due to thermal fluctuations. We see that the thermal fluctuations bring an overall increase in entropy curve. However, in presence of thermal fluctuations, a positive kink, which signifies a maximum increase in the value of entropy, occurs at a certain value of horizon, which is exactly equal to the remnant radius. We observe that the thermal fluctuations, which are characteristics of quantum gravity, lead to stable values of thermodynamic quantities near the remnant radius. In presence of thermal fluctuations, we then derive various corrected thermodynamic potentials and also discuss the validity of first law of black hole thermodynamics for Bardeen black hole.

We construct, by a procedure involving a dimensional reduction from a Chern–Simons theory with borders, an effective theory for (1 + 1)-dimensional superconductor. That system can be in either an ordinary phase or a topological one, depending on the value of two phases, associated to complex order parameters.

In a particle theory model whose most readily discovered new particle is the $\sim 1$ TeV bilepton resonance in same-sign leptons, currently being sought at CERN’s LHC, there exist three quarks ${𝒟}$, ${𝒮}$, ${𝒯}$ which will be bound by QCD into baryons and mesons. We consider the decays of these additional baryons and mesons whose detailed experimental study will be beyond the reach of the 14 TeV CERN collider and accessible only at an O(100 TeV) collider.

For the Schwarzschild black hole, the Bekenstein–Hawking entropy is proportional to the area of the event horizon. For the black holes with two horizons, the thermodynamics is not very clear, since the role of the inner horizons is not well established. Here we calculate the entropy of the Reissner–Nordström black hole and of the Kerr black hole, which have two horizons. For the spherically symmetric Reissner–Nordström black hole, we used several different approaches. All of them give the same result for the entropy and for the corresponding temperature of the thermal Hawking radiation. The entropy is not determined by the area of the outer horizon, and it is not equal to the sum of the entropies of two horizons. It is determined by the correlations between the two horizons, due to which the total entropy of the black hole and the temperature of Hawking radiation depend only on mass M of the black hole and do not depend on the black hole charge Q. For the Kerr and Kerr–Newman black holes, it is shown that their entropy has the similar property: it depends only on mass M of the black hole and does not depend on the angular momentum J and charge Q.

We obtain the wave equation of the perturbation theory governing massless fields of spin 0, 1/2, 1, 3/2 and 2 in accelerating Kerr–Newman–(anti-)de Sitter black holes. We show that the wave equation is separable and the radial and angular equations can both be transformed into Heun’s equation. We approximate Heun’s equation and analyze the solution of radial function near the event horizon. It is worth pointing out that all the field equations collapse to a unique equation which means it can provide a possible way for the analog research between the gravitational field and those other fields.

We introduce quantum heat engines that perform quantum Otto cycle and the quantum Stirling cycle by using a coupled pair of harmonic oscillator as its working substance. In the quantum regime, different working medium is considered for the analysis of the engine models to boost the efficiency of the cycles. In this work, we present Otto and Stirling cycle in the quantum realm where the phase space is non-commutative in nature. By using the notion of quantum thermodynamics, we develop the thermodynamic variables in non-commutative phase space. We encounter a catalytic effect (boost) on the efficiency of the engine in non-commutative space (i.e. we encounter that the Stirling cycle reaches near to the efficiency of the ideal cycle) when compared with the commutative space. Moreover, we obtained a notion that the working medium is much more effective for the analysis of the Stirling cycle than that of the Otto cycle.

In this paper, the higher-dimensional collapse of homogeneous isotropic perfect fluid is studied by considering the geometry of five-dimensional spherically symmetric metric. Using equations of state for different fields like dust, radiation and stiff fluid with and without cosmological constant $\mathrm{\Lambda }$, the gravitational collapse is studied. The results are compared with the usual four-dimensional study in [A. V. Astashenok, K. Mosani, S. D. Odintsov and G. C. Samanta, Int. J. Geom. Methods Mod. Phys. 16, 1950035 (2019)]. It is found that the collapse rate is faster in five-dimensional spacetime as compared to four-dimensional case supporting the cosmic censorship hypothesis.

Computer modeling was applied to the study of $(n,\alpha )$ transmutations in ${\mathrm{\text{Si}}}_3{\mathrm{\text{N}}}_4$ nanoparticles under the influence of neutrons at different energies. The modeling was separately performed for each Si and N atoms in the ${\mathrm{\text{Si}}}_3{\mathrm{\text{N}}}_4$ nanoparticles and the effect of neutrons on transmutations was investigated. The simulations were conducted individually for each stable isotope due to different effective cross-section of the probability of transmutation in the different types of isotopes of silicon and nitrogen atoms. Effective cross-section spectra of $(n,\alpha )$ transmutation in Si and N atoms were comparatively studied.

An extensive study of $\alpha$-decay half-lives for various decay chains of isotopes of $Z=120$ is performed within the axially deformed relativistic mean-field (RMF) formalism by employing the NL3, NL3${}^{\ast }$, and DD-ME2 parameter set. The structural properties of the nuclei appearing in the decay chains are explored. The binding energy, quadrupole deformation parameter, root-mean-square charge radius, and pairing energy are calculated for the even–even isotopes of $Z=100\text{–}120$, which are produced in five different $\alpha$-decay chains, namely, ${}^{296}120\to {}^{260}\mathrm{\text{No}}$, ${}^{298}120\to {}^{262}\mathrm{\text{No}}$, ${}^{300}120\to {}^{264}\mathrm{\text{No}}$, ${}^{302}120\to {}^{266}\mathrm{\text{No}}$, and ${}^{304}120\to {}^{268}\mathrm{\text{No}}$. A superdeformed prolate ground state is observed for the heavier nuclei, and gradually the deformation decreases towards the lighter nuclei in the considered decay chains. The RMF results are compared with various theoretical predictions and experimental data. The $\alpha$-decay energies are calculated for each decay chain. To determine the relative numerical dependency of the half-life for a specific $\alpha$-decay energy, the decay half-lives are calculated using four different formulas, namely, Viola–Seaborg, Alex–Brown, Parkhomenko–Sobiczewski and Royer for the above said five $\alpha$-decay chain. We notice a firm dependency of the half-life on the $\alpha$-decay formula in terms of $Q_{\alpha }$-values for all decay chains. Further, this study also strengthens the prediction for the island of stability in terms of magic number at the superheavy valley in the laboratories.