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EMU Physics Department Academic Staff Members Sakalli and Ovgun's Article Becomes the Most Read Publication in Cyprus

Eastern Mediterranean University, Arts and Sciences Faculty, Physics Department academic staff member Assoc. Prof. Dr. İzzet Sakallı and Physics Department PhD student Ali Övgün’s latest article entitled Black Hole Radiation Of Massive Spin-2 Particles has been accepted for publication by the European Journal of Physics Plus ( (SCI-1.377 Impact Factor), a notable journal of Physics operating under Springer Publishers.

As a candidate of the best examples of Mathematical Physics, Sakalli's and Övgün’s publication has been selected as the mostly read article throughout Cyprus by Researchgate (   At the same time, with over 3000 downloads taking place between 16 and 22 May, the said article has been nominated as the mostly downloaded article in the fields of Mathematical Physics, Cosmology and Astrophysics.

Forty years ago, Stephen Hawking famously announced that black holes should have the ability to thermally create and emit sub-atomic particles until they are completely depleted of their energy, known as Hawking radiation. This also suggested that black holes aren’t completely black and they do not live forever. Hawking explained how the strong gravitational field around a black hole can affect the production of matching pairs of particles and anti-particles, as is happening all the time in empty space according to quantum theory.

If the particles are created just outside the event horizon of a black hole, then it is possible that the positive member of the pair may escape - observed as thermal radiation emitting from the black hole - while the negative particle may fall back into the black hole, and in this way the black hole would gradually lose mass.  It has raised one of the most serious problems for the foundations of theoretical physics, since it says that general relativity and quantum theory cannot be compatible: general relativity predicts black holes will form, and then the explicit computation of vacuum fluctuations around the black hole background shows that the emitted radiation does not carry the information of the matter that made the hole. Hawking had said that if an object falls into a black hole, the only information that is retained are the quantum mechanical properties of mass, spin, and charge. All other information was stripped away. The problem with this is that quantum mechanics is built on the idea that information can’t be lost. If information can be lost, then quantum mechanics isn’t a secure theoretical structure. Hawking, as a relativist, was more concerned with maintaining the theoretical structure of general relativity, so he was okay with the information being lost if it had to be.

A first important step toward the understanding of elementary and composite particles in a relativistic context was made by Klein and Gordon. Their resultant equation, the so-called Klein-Gordon equation, is one of the powerful equations that describes the dynamics of the relativistic spin-0 particles (scalar bosons, pions, scalar mesons, and also Higgs particles) in any geometry. However, in nature many elementary particles have spin and Dirac introduced the correct form of the equation for fermions with spin-1/2 (such as electrons,quarks, and leptons). Then, Proca derived an equation for the massive spin-1 particles (vector particles: W and Z bosons and gluons) which play crucial role in the fundamental interactions as being the force carriers: the W and Z bosons for the weak interaction, and the gluons for the strong interaction. The Proca equation reduces to the Maxwell equation with the limit of the zero masses (photons). In the standard model, experimental verification of the fundamental particles has only been made for the particles having spin 1 and less. However, theoretical physics prescribes that graviton (massless boson) which is the mediator of the gravitational force must have spin-2. Nowadays, one of the trend subjects in physics is the massive gravity theory. This is a theory of gravity that modifies general relativity by endowing the graviton with mass. In the classical theory, this means that gravitational waves obey a massive wave equation and hence travel at speeds below the speed of light. A theory of a massive spin-2 field propagating in a spacetime background was discovered long ago by Fierz and Pauli: the so-called Fierz-Pauli equations (FPEs). However, it was understood in the 1970s that the massive graviton theories have some drawbacks. These theories mainly suffer from the inevitable inclusion of ghost modes and the problem of the general relativity limit while the graviton’s mass vanishes. Although some solutions to those problems exists in three dimensions, they could not be solved in four dimensions until the work of D’Amico et al. On the other hand, LIGO and Virgo collaborations’ observations have recently confirmed the existence of gravitational waves. Although these experiments cannot detect individual gravitons, however they might provide information about certain properties of the graviton. Very recently, FPEs have been reformulated by Koenigstein et al  which is going to be employed in our present study for the derivation of the HR arising from quantum tunneling of the massive gravitons through the event horizon of a generic static and spherically symmetric (3+1) dimensional black hole. To the best of our knowledge, this problem has not been studied before. In this respect, the present study aims to fill this gap in the literature.