Acoustics of tachyon Fermi gas

Trojan, Ernst; Vlasov, George V.

doi:10.1103/physrevd.83.124013

Cited by 7 publications

(20 citation statements)

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“…Absolute stiff matter, which may appear in various problems in astrophysics. Particularly, it is often considered in the interior of neutron stars and problems of cosmology [39]. For this kind of matter the equation of state is u = 1.…”

Section: Noether Gauge Symmetries In Gaussbonnet Dilatonic Gravitymentioning

confidence: 99%

Noether gauge symmetry approach in Gauss–Bonnet dilatonic theory of gravity

Hussain

Mahomed

2012

Can. J. Phys.

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The approach of Noether symmetries with gauge term in the Gauss-Bonnet dilatonic theory of gravity is used for different values of the state parameter, u, of the background matter. It is found that for u = -1 (dark energy Universe), u = 0 (matter-dominated Universe), and u = 1 (the case of stiff matter), for the existence of Noether gauge symmetries, the potential V(f) and the coupling of the Gauss-Bonnet term with gravity L(f) are obtained as exponential functions of the scalar field f. For the case of arbitrary u the coupling parameter L(f) is found as a linear function of the scalar field f and the potential is a constant, for the existence of Noether gauge symmetries. Here it is observed that both the potential and coupling parameter depend on the evolutionary history of the Universe.Résumé : Nous utilisons l'approche de Noether pour les symétries avec terme de jauge, dans une théorie de Gauss-Bonnet de la gravité avec dilaton, pour différentes valeurs du paramètre d'état u de la matière constituant le fond. Nous trouvons, dans les cas u = -1 (univers dominé par l'énergie sombre), u = 0 (univers dominé par la matière) et u = 1 (matière rigide), qu'afin de garantir les symétries de jauge de Noether, le potentiel V(f) et le couplage du terme de Gauss-Bonnet avec la gravité L(f) apparaissent comme des fonctions exponentielles du champ scalaire f. Pour des valeurs autres arbitraires de u, le paramètre de couplage L(f) est obtenu comme une fonction linéaire du champ scalaire f et le potentiel est constant, ce qui assure une symétrie de jauge de Noether. Nous observons ici que le potentiel et la constante de couplage dépendent de l'évolution historique de l'univers.[Traduit par la Rédaction]

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Section: Noether Gauge Symmetries In Gaussbonnet Dilatonic Gravitymentioning

confidence: 99%

Noether gauge symmetry approach in Gauss–Bonnet dilatonic theory of gravity

Hussain

Mahomed

2012

Can. J. Phys.

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“…So far, many investigators used higher spin tachyons to explain different phenomena [14][15][16][17][18][19][20][21][22][23]. For example, some authors consider a Fermi gas of free tachyons in the frames of statistical thermodynamics and mechanics of continuous medium [17]. They claim that apart from any possible theoretical speculation, there are the physical principles to test this theory [18].…”

Section: Introductionmentioning

confidence: 99%

“…Clearly, the scalar string tachyon couldn't produce this type of inflation and we are forced to introduce spinor string tachyon as the main cause of spinor inflation in four dimensional universe. So far, many investigators used higher spin tachyons to explain different phenomena [14][15][16][17][18][19][20][21][22][23]. For example, some authors consider a Fermi gas of free tachyons in the frames of statistical thermodynamics and mechanics of continuous medium [17].…”

Section: Introductionmentioning

confidence: 99%

Bianchi Type I Cosmology with Scalar and Spinor Tachyon

2014

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Recently, some authors propose a scenario where inflation is driven by scalar and spinor fields. In this scenario, the universe undergoes anisotropic inflationary expansion due to a preferred direction dominated by spinor. The main question arises that what is the origin of spinor inflation in 4D Universe? To answer to this question , we propose a new model in super string theory that allows to take into account the spinor string tachyon in additional to scalar one which stretch between branes and antibranes. In this model, the inflation of 4D Universe is controlled by the spinor type of tachyon and evolves from nonphantom phase to phantom one and consequently, phantom-dominated era of the universe accelerates and ends up in big-rip singularity. We test our model against WMAP and Planck data and obtain the ripping time. We find that the finite time that Big Rip singularity occurs is t = 65(Gyr). According to our calculations, N 60 case leads to n s 0.96, where N and n s are the number e-folds and the spectral index respectively. Thus our results are consistent with experimental data and thus the spinor inflationary model works.

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“…In conclusion, the arguments in [1,3] to consider a tachyon ideal gas at sufficiently low density either as an unstable c s 1 matter or as an exotic P E matter have no theoretical grounds.…”

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confidence: 99%

“…In [3] an attempt is made to resolve a confusion of Ref. [1] with the well-established thermodynamic relations by using the following energy spectrum of a tachyon…”

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confidence: 99%

Comment on “Acoustics of tachyon Fermi gas”

Burmistrov

2012

Phys. Rev. D

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In contrast to Trojan and Vlasov [1], it is found that an ideal Fermi gas of tachyons has a subluminous velocity of sound for any particle density and, therefore, the causality condition for a tachyon gas holds always true. Also, an ideal Fermi gas of tachyons never possesses an exotic equation of state with the pressure exceeding the energy density.PACS numbers: 47.75.+f, 03.30.+p, 04.20.Gz, Recently, Trojan and Vlasov [1] have reported the acoustic properties of tachyon Fermi ideal gas at zero temperature. In this study they assert that the Fermi gas of free tachyons, i.e., particles with the energy spectrum, should be unstable if the particle density n of a gas is below some critical value n T because its sound velocity c s exceeds the speed of light, and thus the causality principle cannot be satisfied. In addition, authors [1] have also arrived at the next assertion that the gas of tachyons may represent an example of the so-called stiff matter when the pressure P exceeds the energy density E, i.e., P > E.Both the statements are erroneous. The false conclusions result from using incorrect equation (4) where µ is the chemical potential and γ is the degeneracy factor. For T = 0, the case of interest in [1], one hasis the Fermi energy and E is the energy density of a gas. Using E from [1],gives another result for the pressure of a tachyon Fermi ideal gas at T = 0In addition, the above expression agrees completely with the determination of the pressure as a derivative of the total energy EV over gas volume V with the opposite signThe square of the sound velocity c s is then given by c 2 s = ∂E/∂P = 1 3where β = k F /m 1 is a ratio of the Fermi momentum to the tachyon mass. Thus, unlike [1], the sound velocity, changing between 1/ √ 2 and 1/ √ 3, is always smaller than the speed of light and the causality principle c s < 1 does not break down for any density of ideal tachyon gas.As it concerns the ratio of pressure to energy density, it varies from 1/2 in the low density limit to 1/3 for the high density limit. As a result, the hypothesis [1] that the low density gas of free tachyon can represent an example of the so-called absolute stiff or hyperstiff matter with the equation of state P E proves to be invalid as well.In [3] an attempt is made to resolve a confusion of Ref.[1] with the well-established thermodynamic relations by using the following energy spectrum of a tachyonHowever, such energy spectrum does not satisfy the relativity principle that the square of four-vector (ε, k) must be an identical scalar within the whole region of permissible k, i.e., ε 2 k − k 2 = const.Obviously, this condition breaks down for the spectrum proposed.In conclusion, the arguments in [1,3] to consider a tachyon ideal gas at sufficiently low density either as an unstable c s 1 matter or as an exotic P E matter have no theoretical grounds.

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Acoustics of tachyon Fermi gas

Cited by 7 publications

References 27 publications

Noether gauge symmetry approach in Gauss–Bonnet dilatonic theory of gravity

Noether gauge symmetry approach in Gauss–Bonnet dilatonic theory of gravity

Bianchi Type I Cosmology with Scalar and Spinor Tachyon

Comment on “Acoustics of tachyon Fermi gas”

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