Quasinormal frequencies of asymptotically flat two-dimensional black holes

We discuss whether the minimally coupled massless Klein-Gordon and Dirac fields have well defined quasinormal modes in single horizon, asymptotically flat two-dimensional black holes. To get the result we solve the equations of motion in the massless limit and we also calculate the effective potentials of Schrödinger type equations. Furthermore we calculate exactly the quasinormal frequencies of the Dirac field propagating in the two-dimensional uncharged Witten black hole. We compare our results on its quasinormal frequencies with other already published.     

Dirac quasinormal modes of <Emphasis Type="Italic">D</Emphasis>-dimensional de Sitter spacetime

We find exact solutions to the Dirac equation in D-dimensional de Sitter spacetime. Using these solutions we analytically calculate the de Sitter quasinormal (QN) frequencies of the Dirac field. For the massive Dirac field this computation is similar to that previously published for massive fields of half-integer spin moving in four dimensions. However to calculate the QN frequencies of the massless Dirac field we must use distinct methods in odd and even dimensions, therefore the computation is different from that already known for other massless fields of integer spin.     

Massive Quasinormal Modes of a Schwarzschild-de Sitter Black Hole with a Global Monopole

Using the WKB approximation, we evaluate both the massless and massive scalar and Dirac fields quasinormal modes (QNMs) of a Schwarzschild-de Sitter black hole. The result shows that the field with higher masses and larger cosmological constant λ will decay more slowly. We also found that the global monopole is similar to a factor to modify the κ of Dirac field or l of scalar field, where κ is the angular momentum number of Dirac field, and l is the angular momentum number of scalar field.     

Quasinormal modes of a two-dimensional black hole

For a two-dimensional black hole we determine the quasinormal frequencies of the Klein–Gordon and Dirac fields. In contrast to the well known examples whose spectrum of quasinormal frequencies is discrete, for this black hole we find a continuous spectrum of quasinormal frequencies, but there are unstable quasinormal modes. In the framework of the Hod and Maggiore proposals we also discuss the consequences of these results on the form of the entropy spectrum for the two-dimensional black hole.     

Quasinormal frequencies of asymptotically anti-de Sitter black holes in two dimensions

We calculate exactly the quasinormal frequencies of Klein–Gordon and Dirac test fields propagating in 2D uncharged Achucarro–Ortiz black hole. For both test fields we study whether the quasinormal frequencies are well defined in the massless limit. We use their values to discuss the classical stability of the quasinormal modes in uncharged Achucarro–Ortiz black hole and to check the recently proposed Time Times Temperature bound. Furthermore we extend some of these results to the charged Achucarro–Ortiz black hole.     

Massive Charged Quasinormal Modes of a Reissner-Nordström Black Hole

Using the WKB method and HYBRD program, we evaluate the low-lying massive charged scalar and Dirac field quasinormal modes (QNMs) of a Reissner-Nordström black hole. We discuss the real and imaginary parts of QNMs vary with the charge of black hole, the masses and charges of scalar and Dirac fields.     

A comparative study of Dirac quasinormal modes of charged black holes in higher dimensions

In this work we study the Dirac quasinormal modes of higher dimensional charged black holes. Higher dimensional Reissner–Nordström type black holes as well as charged black holes in Einstein–Gauss–Bonnet theories are studied for fermionic perturbations using WKB method. A comparative study of the quasinormal modes in the two different theories of gravity has been performed. The behavior of the frequencies with the variation of black hole parameters as well as with the variation of space-time dimensions is studied. We also study the large multipole number limit of the black hole potential in order to look for an analytic expression for the frequencies.     

Schwinger's method for the fermionic Casimir effect

The Casimir energy of a massive Dirac field confined between two parallel infinite plates is computed using a method proposed by Schwinger. The massless case is obtained as a limit of the massive case. The boundary conditions are those of zero current through the plates, as inspired by quark confinement in the MIT bag model for hadrons. We use an analytical continuation method of regularization which allows the employment of Epstein function techniques. The calculation using Schwinger's original regularization by a cutoff in proper time is also outlined.     

Massive scalar field quasinormal modes of a Schwarzschild black hole surrounded by quintessence

We present the quasinormal frequencies of the massive scalar field in the background of a Schwarzchild black hole surrounded by quintessence with the third-order WKB method. The mass of the scalar field u plays an important role in studying the quasinormal frequencies, the real part of the frequencies increases linearly as mass of the field u increases, while the imaginary part in absolute value decreases linearly which leads to damping more slowly than the massless scalar field. The frequencies have a limited value, so it is easier to detect the quasinormal modes. Moreover, owing to the presence of the quintessence, the massive scalar field damps more slowly.      

Dirac Quasinormal Modes of Reissner-Nodstrom Black Hole Surrounded by Quintessence

Using the third-order WKB approximation, we evaluate the quasinormal frequencies of massless Dirac field perturbation around a Reissner Nordstrom black hole surrounded by a static and spherically symmetric quintessence. We study the variation of quasinormal frequencies with the quintessential state parameter ε, the total angular momentum number ｜k｜, the charge Q, and the overtone number n changes, respectively. Moreover, from the results we obtained, we find that the massless Dirac field damps more slowly due to the presence of quintessence.     

Quasinormal modes of D-dimensional de Sitter spacetime

We calculate the exact values of the quasinormal frequencies for an electromagnetic field and a gravitational perturbation moving in D-dimensional de Sitter spacetime (D ≥ 4). We also study the quasinormal modes of a real massive scalar field and compare our results with those of other references.     

Quasinormal Modes of Spherical Symmetrical Black Hole with x-Matter

In this paper, we use expansion method with eikonal limit to calculate the scalar and Dirac quasinormal modes of black hole with x-matter, which is a spherical symmetrical vacuum black hole in a brane-world scenario. The spacetime includes x-matter as the dark energy. From the results, we find the x-matter accelerates quasinormal frequency and slows damping rate of amplitude.     

Absorption and quasinormal modes of classical fields propagating on 3D and 4D de Sitter spacetime

We extensively study the exact solutions of the massless Dirac equation in 3D de Sitter spacetime that we published recently. Using the Newman-Penrose formalism, we find exact solutions of the equations of motion for the massless classical fields of spin s= 12,1,2 and to the massive Dirac equation in 4D de Sitter metric. Employing these solutions, we analyze the absorption by the cosmological horizon and de Sitter quasinormal modes. We also comment on the results given by other authors.     

Entropy spectrum of the D-dimensional massless topological black hole

There are exact solutions to Einstein’s equations with negative cosmological constant that represent black holes whose event horizons are manifolds of negative curvature, the so-called topological black holes. Among these solutions there is one, the massless topological black hole, whose mass is equal to zero. Hod proposes that in the semiclassical limit the asymptotic quasinormal frequencies determine the entropy spectrum of the black holes. Taking into account this proposal, we calculate the entropy spectrum of the massless topological black hole and we compare with the results on the entropy spectra of other topological black holes.     

Superradiant Instability of D-Dimensional Reissner–Nordstr?m Black Hole Mirror System

We analytically study the superradiant instability of charged massless scalar field in the background of D-dimensional Reissner–Nordstr¨om(RN) black hole caused by mirror-like boundary condition. By using the asymptotic matching method to solve the Klein–Gordon equation that governs the dynamics of scalar field, we have derived the expressions of complex parts of boxed quasinormal frequencies, and shown they are positive in the regime of superradiance.This indicates the charged scalar field is unstable in D-dimensional Reissner–Nordstr¨om(RN) black hole surrounded by mirror. However, the numerical work to calculate the boxed quasinormal frequencies in this system is still required in the future.     

Transmission through biased graphene strip

We solve the 2D Dirac equation describing graphene in the presence of a linear vector potential. The discretization of the transverse momentum due to the infinite mass boundary condition reduced our 2D Dirac equation to an effective massive 1D Dirac equation with an effective mass equal to the quantized transverse momentum. We use both a numerical Poincaré map approach, based on space discretization of the original Dirac equation, and a direct analytical method. These two approaches have been used to study tunneling phenomena through a biased graphene strip. The numerical results generated by the Poincaré map are in complete agreement with the analytical results.     

Black holes in massive gravity: quasi-normal modes of scalar perturbations

We have studied quasinormal modes of scalar perturbations of a black hole in massive gravity. The parameters of the theory, such as the mass of the black hole, the scalar charge of the black hole and the spherical harmonic index is varied to see how the corresponding quasinormal frequencies change. We have also studied the massive scalar field perturbations. Most of the work is done using WKB approach while sections are devoted to compute quasinormal modes via the unstable null geodesics approach and the Pöschl–Teller approximation. Comparisons are done with the Schwarzschild black hole.     

Fermionic quasinormal modes for two-dimensional Hořava–Lifshitz black holes

To obtain fermionic quasinormal modes, the Dirac equation for two types of black holes is investigated. It is shown that two different geometries lead to distinctive types of quasinormal modes, while the boundary conditions imposed on the solutions in both cases are identical. For the first type of black hole, the quasinormal modes have continuous spectrum with negative imaginary part that provides the stability of perturbations. For the second type of the black hole, the quasinormal modes have a discrete spectrum and are completely imaginary.     

Quasinormal modes of the BTZ black hole under scalar perturbations with a non-minimal coupling: exact spectrum

We perturb the non-rotating BTZ black hole with a non-minimally coupled massless scalar field, and we compute the quasinormal spectrum exactly. We solve the radial equation in terms of hypergeometric functions, and we obtain an analytical expression for the quasinormal frequencies. In addition, we compare our analytical results with the 6th order semi-analytical WKB method, and we find an excellent agreement. The impact of the nonminimal coupling as well as of the cosmological constant on the quasinormal spectrum is briefly discussed.     

Quasinormal modes of non-Abelian hyperscaling violating Lifshitz black holes

We study the quasinormal modes of scalar field perturbations in the background of non-Abelian hyperscaling violating Lifshitz black holes. We find that the quasinormal frequencies have no real part so there is no oscillatory behavior in the perturbations, only exponential decay, that is, the system is always overdamped, which guarantees the mode stability of non-Abelian hyperscaling violating Lifshitz black holes. We determine analytically the quasinormal modes for massless scalar fields for a dynamical exponent \(z=2\) and hyperscaling violating exponent \(\tilde{\theta }>-2\). Also, we obtain numerically the quasinormal frequencies for different values of the dynamical exponent and the hyperscaling violating exponent by using the improved asymptotic iteration method.