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Christian Corda

Publications and source records attributed to Christian Corda.

At least 37 records · Page 2Linked to original sources
arXiv2021

A new experiment for the gravitational waves detection

A new experiment for the gravitational waves (GWs) detection is proposed. It is indeed shown that the effect of GWs on sound waves (SWs) in a fluid is that GWs vary the pressure of the fluid by crossing it. This variation can be found by analysing the gauge of the local observer. It is shown that one can, in principle, detect GWs through the proposed new experiment. The variation of the pressure of the fluid, which represents detected signals, are indeed much higher than the correspondent values of GWs amplitudes. The examples of rotating neutron stars (NSs) and relic GWs are discussed. Remarkably, a confrontation of the proposed new method with a previous paper of Singh et al. on a similar approach shows a possible improvement of the sensitivity concerning the potential detection of GWs. It must be emphasized that this proposed procedure may be difficult in practical experiments because of the presence of different types of noise. For this reason, a Section of the paper is dedicated to the discussion of such noises. On the other hand, this paper must be considered as being pioneering in the new proposed approach. Thus, we hope in future, more precise studies of the noise which concerns the proposed new experiment will be done.

physics.gen-ph↗
arXiv2021

The quantum black hole as a gravitational hydrogen atom

Nathan Rosen's quantization approach to the gravitational collapse is applied in the simple case of a pressureless "star of dust" by finding the gravitational potential, the Schrodinger equation and the solution for the collapse's energy levels. By applying the constraints for a Schwarzschild black hole (BH) and by using the concept of BH effective state, previously introduced by one of the authors (CC), the BH quantum gravitational potential, Schrodinger equation and the BH energy spectrum are found. Remarkably, such an energy spectrum is in agreement (in its absolute value) with the one which was conjectured by Bekenstein in 1974 and consistent with other ones in the literature. This approach also permits to find an interesting quantum representation of the Schwarzschild BH ground state at the Planck scale. Moreover, two fundamental issues about BH quantum physics are addressed by this model: the area quantization and the singularity resolution. As regards the former, a result similar to the one obtained by Bekenstein, but with a different coefficient, has been found. About the latter, it is shown that the traditional classical singularity in the core of the Schwarzschild BH is replaced, in a full quantum treatment, by a two-particle system where the two components strongly interact with each other via a quantum gravitational potential. The two-particle system seems to be non-singular from the quantum point of view and is analogous to the hydrogen atom because it consists of a "nucleus" and an "electron".

gr-qc↗
arXiv2020

Quantum Hair on Colliding Black Holes

Abstract Black hole collision produce gravitational radiation which is generally thought in a quantum limit to be gravitons. The stretched horizon of a black hole contains quantum information, or a form of quantum hair, which in a coalescence of black holes participates in the generation of gravitons. This may be facilitated with a Bohr-like approach to black hole (BH) quantum physics with quasi-normal mode (QNM) approach to BH quantum mechanics. Quantum gravity and quantum hair on event horizons is excited to higher energy in BH coalescence. The near horizon condition for two BHs right before collision is a deformed AdS spacetime. These excited states of BH quantum hair then relax with the production of gravitons. This is then argued to define RT entropy given by quantum hair on the horizons. These qubits of information from a BH coalescence should then appear in gravitational wave (GW) data. This is a form of the standard AdS/CFT correspondence and the Ryu-Takayanagi (RT) formula.

physics.gen-ph↗
arXiv2020

Modified Friedmann equations from DSR-GUP

Considering the modified entropy-area relation from DSR-GUP (Doubly special relativity-Generalized uncertainity principle), we obtain the modified Friedmann equations from the first law of thermodynamics at apparent horizon. Due to the importance of GUP at Planck scale, we investigate the Friedmann equations and show the maximum energy density \r{ho} at Planck scale. Since GUP implies a minimal length, we find a minimum apparent horizon which has a potential to remove the Big Bang singularity. Furthermore, we analyse the effects of DSR-GUP on deceleration parameter q for the equation of state p = ω\r{ho} and the flat case. Finally, we check the validity of the generalized second law (GSL) of thermodynamics and show that it is valid all eras of the Universe for any spatial curvature.

gr-qc↗
arXiv2020

Generalized potential for apparent forces: the Coriolis effect

It is well known, from Newtonian physics, that apparent forces appear when the motion of masses is described by using a non-inertial frame of reference. The generalized potential of such forces is rigorously analyzed focusing on their mathematical aspects.

physics.gen-ph↗
arXiv2019

Constraining chameleon field driven warm inflation with Planck 2018 data

We investigate warm inflationary scenario in which the accelerated expansion of the early Universe is driven by chameleon-like scalar fields. Due to the non-minimal coupling between the scalar field and the matter sector, the energy-momentum tensor of each fluid component is not conserved anymore, and the generalized balance equation is obtained. The new source term in the energy equation can be used to model warm inflation. On the other hand, if the coupling function varies slowly, the model reduces to the standard model used for the description of cold inflation. To test the validity of the warm chameleon inflation model, the results for warm inflationary scenarios are compared with the observational Planck2018 Cosmic Microwave Background data. In this regard, the perturbation parameters such as the amplitude of scalar perturbations, the scalar spectral index and the tensor-to-scalar ratio are derived at the horizon crossing in two approximations, corresponding to the weak and strong dissipative regimes. As a general result it turns out that the theoretical predictions of the chameleon warm inflationary scenario are consistent with the Planck 2018 observations.

gr-qc↗
arXiv2019

Mossbauer rotor experiment as new proof of general relativity: Rigorous computation of the additional effect of clock synchronization

We received an Honorable Mention at the Gravity Research Foundation 2018 Awards for Essays on Gravitation by showing that a correct general relativistic interpretation of the Mossbauer rotor experiment represents a new, strong and independent, proof of Einstein's general theory relativity (GTR). Here we correct a mistake which was present in our previous computations on this important issue by deriving a rigorous computation of the additional effect of clock synchronization. Finally, we show that some recent criticisms on our general relativistic approach to the Mossbauer rotor experiment are incorrect, by ultimately confirming our important result.

gr-qc↗
arXiv2019

On the general relativistic framework of the Sagnac effect

The Sagnac effect is usually considered as being a relativistic effect produced in an interferometer when the device is rotating. General relativistic explanations are known and already widely explained in many papers. Such general relativistic approaches are founded on Einstein's equivalence principle (EEP), which states the equivalence between the gravitational "force" and the pseudo-force experienced by an observer in a non-inertial frame of reference, included a rotating observer. Typically, the authors consider the so-called Langevin-Landau-Lifschitz metric and the path of light is determined by null geodesics. This approach partially hides the physical meaning of the effect. It seems indeed that the light speed varies by c\pmωr in one or the other direction around the disk. In this paper, a slightly different general relativistic approach will be used. The different "gravitational field" acting on the beam splitter and on the two rays of light is analyzed. This different approach permits a better understanding of the physical meaning of the Sagnac effect.

gr-qc↗
arXiv2018

New proof of general relativity through the correct physical interpretation of the Mossbauer rotor experiment

In this Essay, we give a correct interpretation of a historical experiment by Kundig on the transverse Doppler shift in a rotating system (Mossbauer rotor experiment). This experiment has been recently first reanalyzed, and then replied by an experimental research group. The results of reanalyzing the experiment have shown that a correct re-processing of Kundig's experimental data gives an interesting deviation of a relative redshift between emission and absorption resonant lines from the standard prediction based on the relativistic dilatation of time. Subsequent new experimental results by the reply of Kundig experiment have shown a deviation from the standard prediction even higher. By using the Equivalence Principle (EP), which states the equivalence between the gravitational "force" and the pseudo-force experienced by an observer in a non-inertial frame of reference (included a rotating frame of reference), here the theoretical framework of the Mossbauer rotor experiment is reanalyzed directly in the rotating frame of reference through a general relativistic treatment. It will be shown that previous analyses missed an important effect of clock synchronization. By adding this new effect, the correct general relativistic prevision is in perfect agreement with the new experimental results. Such an effect of clock synchronization has been missed in various papers in the literature, with some subsequent claim of invalidity of the relativity theory and/or some attempts to explain the experimental results through "exotic" effects. The general relativistic interpretation in this Essay shows, instead, that the new experimental results of the Mossbauer rotor experiment are a new, strong and independent, proof of general relativity.

gr-qc↗
arXiv2018

Space-time can be neither discrete nor continuous

We show that our recent Bohr-like approach to black hole (BH) quantum physics implies that space-time quantization could be energy-dependent. Thus, in a certain sense, space-time can be neither discrete nor continuous. Our approach permits also to show that the "volume quantum" of the Schwarzschild space-time increases with increasing energy during BH evaporation and arrives to a maximum value when the Planck scale is reached and the generalized uncertainty principle (GUP) prevents the total BH evaporation. Remarkably, this result does not depend on the BH original mass. The interesting consequence is that the behavior of BH evaporation should be the same for all Schwarzschild BHs when the Planck scale is approached.

physics.gen-ph↗
arXiv2018

Tunnelling mechanism in non-commutative space with generalized uncertainty principle and Bohr-like black hole

The paper deals with non-thermal radiation spectrum by tunnelling mechanism with correction due to the generalized uncertainty principle (GUP) in the background of non-commutative geometry. Considering the reformulation of the tunnelling mechanism by Banerjee and Majhi, the Hawking radiation spectrum is evaluated through the density matrix for the outgoing modes. The GUP corrected effective temperature and the corresponding GUP corrected effective metric in non-commutative geometry are determined using Hawking's periodicity arguments. Thus, we obtain further corrections to the non-strictly thermal black hole (BH) radiation spectrum which give new final distributions. Then, we show that the GUP and the non-commutative geometry modify the Bohr-like BH recently discussed in a series of papers in the literature. In particular, we find the intriguing result that the famous law of Bekenstein on the area quantization is affected neither by non-commutative geometry nor by the GUP. This is a clear indication of the universality of Bekenstein's result. In addition, we find that both the Bekentsein-Hawking entropy and the total BH entropy to third order approximation are still functions of the BH quantum level.

gr-qc↗
arXiv2018

Ideal gas with a varying (negative absolute) temperature: An alternative to dark energy?

The present work is an attempt to investigate whether the evolutionary history of the Universe from the offset of inflation can be described by assuming the cosmic fluid to be an ideal gas with a specific gas constant but a varying negative absolute temperature (NAT). The motivation of this work is to search for an alternative to the "exotic" and "supernatural" dark energy (DE). In fact, the NAT works as an "effective quintessence" and there is need to deal neither with exotic matter like DE nor with modified gravity theories. For the sake of completeness, we release some clarifications on NATs in Section 3 of the paper.

physics.gen-ph↗
arXiv2018

The future of gravitational theories in the era of the gravitational wave astronomy

We discuss the future of gravitational theories in the framework of gravitational wave (GW) astronomy after the recent GW detections (the events GW150914, GW151226, GW170104, GW170814, GW170817 and GW170608). In particular, a calculation of the frequency and angular dependent response function that a GW detector would see if massive modes from f(R) theories or scalar tensor gravity (STG) were present, allowing for sources incident from any direction on the sky, is shown. In addition, through separate theoretical results which do not involve the recent GW detections, we show that f(R) theories of gravity having a third massless mode are ultimately ruled out while there is still room for STG having a third (massive or massless) mode and for f(R) theories of gravity having a third massive mode.

gr-qc↗
arXiv2017

Gravity with torsion in non-conservative Maxwell-like gauge approach

In this work we take into consideration a generalization of Gauge Theories based on the analysis of the structural characteristics of Maxwell theory, which can be considered as the prototype of such kind of theories (Maxwell-like). Such class of theories is based on few principles related to different orders of commutators between covariant derivatives. Their physical meaning is very simple, and lies in stating that the local transformations of a suitable substratum (the space-time or a particular phase space) and the imposed constraints define a "compensative mechanism" or the "interaction" we want to characterize. After a mathematical introduction, we apply this approach to a modified theory of gravity, in which the algebra of operators of covariant derivatives leads to an additional term in the equation of motion associated with the non-conservation of the energy-moment tensor. This offers the possibility to include, without ad hoc physical assumptions and directly from the formalism, new forms of coupling between matter and energy and the expression of the mixing between gravity and torsion.

gr-qc↗
arXiv2016

The Jeans theorem and the "Tolman-Oppenheimer-Volkov equation" in an exact wave solution of R^2 gravity

Corda, Mosquera Cuesta and Lorduy Gomez have shown that spherically symmetric stationary states can be used as a model for galaxies in the framework of the linearized R^2 gravity. Those states could represent a partial solution to the Dark Matter Problem. Here we discuss an improvement of this work. In fact, as the star density is a functional of the invariants of the associated Vlasov equation, we show that any of these invariants is in its turn a functional of the local energy and the angular momentum. As a consequence, the star density depends only on these two integrals of the Vlasov system. This result is known as the "Jeans theorem". In addition, we find an analogous of the historical Tolman- Oppenheimer-Volkov equation for the system considered in this paper. For the sake of completeness, in the final Section of the paper we consider two additional models which argue that Dark Matter could not be an essential element.

gr-qc↗
arXiv2016

The Mössbauer rotor experiment and the general theory of relativity

This paper is a rebuttal to Eur. Phys. Jour. Plus 130, 191 (2015), which claims that the results in arXiv:1502.04911 (Ann. Phys. 355, 360 (2015)) are incorrect. For this reason, some of the results in arXiv:1502.04911 have been reviewed and clarified. The results in this paper are dedicated to the 100th anniversary of Albert Einstein's presentation of the complete General Theory of Relativity to the Prussian Academy.

gr-qc↗