Generalized second law of thermodynamics in the presence of interacting tachyonic field and scalar (phantom) field

Abstract

In the present work, we have considered tachyonic field, phantom field and scalar field in both interacting and non-interacting situations and investigated the validity of the generalized second law of thermodynamics in a flat FRW universe. We found that in all cases, excepting the phantom field dominated universe, the derivative of the entropy is remaining at negative level and is increasing with the decrease in the redshift. 98.80.Cq, 95.36.+x Since the discovery of the fact that presently there is an accelerating expansion of the universe; different suggestions have been made in order to explain the accelerated expansion. Among the various suggestions, one is the hypothesis of dark energy (DE), which is a fluid of negative pressure representing about 70% of the total energy of the universe [1,2,3,4]. The distinguishing feature of dark energy is that it violates the strong energy condition ρ + 3p > 0 [5]. Strength of this acceleration depends on the theoretical model employed while interpreting the data. A wide range of scenarios have been proposed to explain this acceleration but most of them cannot explain all the features of the universe or they have so many parameters that they are difficult to fit. The models which have been discussed widely in literature are those which consider vacuum energy (cosmological constant) as DE, introduce a fifth element and dub it quintessence (ω > −1) or scenarios named phantom with ω < −1, where ω = p/ρ is a parameter of state [6].One remarkable feature of the phantom model is that the universe will end with a "big rip" (future singularity). That is, for phantom dominated universe, its total lifetime is finite. Before the death of the universe, the phantom dark energy will rip apart all bound structures like the Milky Way, solar system, Earth and ultimately the molecules, atoms, nuclei and nucleons of which we are composed. In the quintessence model, the equation state ω = p/ρ is always in the range −1 ≤ ω ≤ 1 for the potential V (φ) > 0. It has been shown in the reference [7] that the decay of an unstable D-brane produces pressure-less gas with finite energy density that resembles classical dust. The cosmological effects of the tachyon rolling down to its ground state have been discussed by the reference [8]. There have been many works aimed at connecting the string theory with inflation. While doing so, various ideas in string theory based on the concept of branes have proved themselves fruitful. Rolling tachyon matter associated with unstable D-branes has an interesting equation of state which smoothly interpolates between −1 and 0. As the Tachyon field rolls down the hill, the universe experiences accelerated expansion and at a particular epoch the scale factor passes through the point of inflection marking the end of inflation [9].To obtain a suitable evolution of the Universe an interaction is often assumed such that the decay rate should be proportional to the present value of the Hubble parameter for good fit to the expansion history of the Universe as determined...

Modular amplitudes and flux-superpotentials on elliptic Calabi-Yau fourfolds

“…We also show that similar features hold for the genus one amplitude, which is conjectured to be related to the gauge kinetic terms. As in the Calabi-Yau threefold case we find that these amplitudes are related via certain holomorphic anomaly equations, from which they can be reconstructed in simple situations [18][19][20][21][22].…”

“…We aim here to derive corresponding modular anomaly equations. For the K3 case this was done in [44] and for elliptic threefolds in [19,20]. Our strategy will be the following: we study the generic degree 24 hypersurface X 24 in P (1, 1, 1, 1, 8, 12) that has been used by [17] to illustrate the modular structure and we find the modular anomaly equations.…”

“…For this to be a supersymmetric minimum we also have to check that D i W = 0. In flat coordinates t i c this condition reads 20) where K i = ∂ i K and K is the Kähler potential…”

Canonical and phantom scalar fields as an interaction of two perfect fluids

“…Now from Eqs. (8) and (21), and by taking into account Eq. (22), we have that the potential is given by…”

Thermodynamics and holography of tachyon cosmology

“…In [49] the validity of thermodynamical laws in a dark energy filled universe has been discussed and in [50]- [52] the laws of thermodynamics in modified gravity theories have been investigated. In [53] the author deals with the second law of thermodynamics in the presence of interacting tachyonic field and another scalar field. Also, in some HDE and IHDE models the authors have tried to discuss the laws of thermodynamics in flat and non-flat universes [54]- [57].…”