Gravitational wave background discovered by NANOGrav as evidence of a cyclic universe

Gorkavyi, Nick

doi:10.1016/j.newast.2021.101698

Cited by 6 publications

(3 citation statements)

References 26 publications

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“…In addition to SMBHBs and cosmic strings, there might be other sources of a commonspectrum process, which are worth considering. Some of the most suggestive and physically impactful, if confirmed, are inflation and reheating [61], BBHs from the previous aeon merged during the Big Crunch [62,63] in cyclic conformal cosmological models of the Universe [64], massive gravity [65], and axion-like particles [66]. In particular, a GWB produced by quantum fluctuations of the gravitational field during the inflationary epoch is actually predicted within the context of the standard cosmological model Λ-Cold Dark Matter (ΛCDM), so its discovery would be crucial for probing the evolution of the Universe.…”

Section: Current Resultsmentioning

confidence: 99%

Principles of Gravitational-Wave Detection with Pulsar Timing Arrays

2021

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Pulsar timing uses the highly stable pulsar spin period to investigate many astrophysical topics. In particular, pulsar timing arrays make use of a set of extremely well-timed pulsars and their time correlations as a challenging detector of gravitational waves. It turns out that pulsar timing arrays are particularly sensitive to ultra-low-frequency gravitational waves, which makes them complementary to other gravitational-wave detectors. Here, we summarize the basics, focusing especially on supermassive black-hole binaries and cosmic strings, which have the potential to form a stochastic gravitational-wave background in the pulsar timing array detection band, and the scientific goals on this challenging topic. We also briefly outline the recent interesting results of the main pulsar timing array collaborations, which have found strong evidence of a common-spectrum process compatible with a stochastic gravitational-wave background and mention some new perspectives that are particularly interesting in view of the forthcoming radio observatories such as the Five hundred-meter Aperture Spherical Telescope, the MeerKAT telescope, and the Square Kilometer Array.

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Section: Current Resultsmentioning

confidence: 99%

Principles of Gravitational-Wave Detection with Pulsar Timing Arrays

2021

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“…In more realistic models of cosmology, it is necessary to consider the important role of gravitational waves [34][35][36]. However, we believe that gravitational radiation does not have a significant impact on the question of the evolution of the Universe's entropy.…”

Section: Discussionmentioning

confidence: 99%

Entropy of Black Holes and an Oscillating Universe

Gorkavyi

2023

Preprint

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The model of an oscillating universe proposed by A. Friedmann in 1922 dominated cosmology for a long time. R. Tolman put forward a thermodynamic argument against the cyclic cosmological model, believing that entropy should accumulate from cycle to cycle. J. Bekenstein and S. Hawking discovered a tremendous amount of entropy associated with black holes. This discovery led to the conclusion that the majority of the Universe's entropy is contained in black holes. N. Poplawski considers a Universe that oscillates within a black hole. This paper analyzes the relationship between the entropy of black holes and the oscillating Universe inside a large black hole. It is demonstrated that the entropy of a black hole can only be defined for an external observer. For an observer inside the black hole, its entropy is zero. This opens up the possibility of constructing a cyclic cosmology in which entropy and the size of the visible part of the Universe change strictly periodically. This does not violate the second law of thermodynamics because the continuous accumulation of entropy from cycle to cycle pertains to the surface of the big black hole, which is invisible to the internal observer.

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“…The Hubble rate is vanished and changed the sign at maximum energy in a finite value of scale factor. The relic gravitational waves from the merging of a large number of black holes in a collapsed phase of the universe in the pre-bounce regime, may be regarded as good evidence of a cyclic universe [34]. Among many models of bouncing cosmology, i.e.…”

Section: Introductionmentioning

confidence: 99%

Unifying turnaround-bounce cosmology in a cyclic universe considering a running vacuum model

Khodam-Mohammadi

2022

Preprint

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Among many models which can describe the bouncing cosmology, A matter bounce scenario that is deformed by a running vacuum model of dark energy (RVM-DE) has been interested. In this research, I show that a class of RVM-CDM (cold dark matter) model can also describe a cyclical cosmology in which the universe undergoes cycles of expansion to the contraction phase and vice versa. To this end, following our previous work, I consider one of the most successful class of RVM-CDM model in bouncing cosmology, ρ x = n 0 + n 2 H 2 + n 4 H 4 , in which the power spectral index gets a red tilt and the running of the spectral index may give a negative value by choosing the appropriate value of parameters (n 0 , n 2 , n 4 ), which is consistent with the cosmological observations. It is worthwhile to mention that most matter bounce models do not produce this negative value. However, the main purpose of this article is to investigate the RVM-CDM model in the turnaround phase. Far from the bounce in a phantom expanding universe, the turnaround conditions are investigated before the occurrence of a sudden big rip. By analyzing the Hubble parameter, equation of state parameter, and deceleration parameter around the turnaround, we show that a successful turnaround may occur after an expansion in an interacting case of RVM-CDM by choosing the appropriate value of parameters. A minimum value for the interaction parameter is obtained and also find any relation between other model parameters. Finally, the effect of each parameter on a turnaround is studied, and we see that the transition time from accelerating to decelerating expansion can occur earlier for larger values of interaction parameter. Also, in several graphs, the effect of the second term in DE density, including H 2 , is studied, and we see that by increasing its coefficient, n 2 , the transition point leads to lower values.

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Gravitational wave background discovered by NANOGrav as evidence of a cyclic universe

Cited by 6 publications

References 26 publications

Principles of Gravitational-Wave Detection with Pulsar Timing Arrays

Principles of Gravitational-Wave Detection with Pulsar Timing Arrays

Entropy of Black Holes and an Oscillating Universe

Unifying turnaround-bounce cosmology in a cyclic universe considering a running vacuum model

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