Tachyonic field interacting with scalar (phantom) field

Abstract

In this letter, we have considered the universe is filled with the mixture of tachyonic field and scalar or phantom field. If the tachyonic field interacts with scalar or phantom field, the interaction term decays with time and the energy for scalar field is transferred to tachyonic field or the energy for phantom field is transferred to tachyonic field. The tachyonic field and scalar field potentials always decrease, but phantom field potential always increases.Keywords: acceleration, tachyonic field, scalar field, phantom field Recent measurements of the luminosity-redshift relations observed [1,2] for a number of newly discovered type Ia supernova indicate that at present the universe is expanding in a accelerated manner. This has given rise to a lot of dark energy models [3][4][5][6], which are supposed to be the reason behind this present acceleration. This mysterious fluid called dark energy is believed to dominate over the matter content of the Universe by 70 % and to have enough negative pressure as to drive present day acceleration. Most of the dark energy models involve one or more scalar fields with various actions and with or without a scalar field potential [7]. The ratio w between the pressure and the energy density of the dark energy seems to be near of less than −1, −1.62Numerous models of dark energy exist. There is much interest now in the tachyon cosmology [9] where the appearance of tachyon is basically motivated by string theory [10]. It has been recently shown by Sen [11,12] 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 Gibbons [13]. Rolling tachyon matter associated with unstable D-branes has an interesting equation of state which smoothly interpolates between −1 and 0 i.e., −1 < w < 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 [10]. The tachyonic matter might provide an explanation for inflation at the early epochs and could contribute to some new form of cosmological dark matter at late times [14]. Inflation under tachyonic field has also been discussed in ref. [9,15,16]. Also the tachyon field has a potential which has an unstable maximum at the origin and decays to almost zero as the field goes to infinity. Depending on various forms of this potential following this asymptotic behaviour a lot of works have been carried out on tachyonic dark energy [6,17]. Sami et al [18] have discussed the cosmological prospects of rolling tachyon with exponential potential.The phantom field (with negative kinetic energy) [19] was also proposed as a candidate for dark energy as it admits sufficient negative pressure (w < −1). One remarkable feature of the phantom model is that the universe will end * Electronic address: surajit_2008@yahoo.co.in † Electronic address: ujjaldebnat...

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

“…The energy density ρ 2 and pressure p 2 for scalar field (or phantom field) φ 2 with potential V 2 (φ 2 ) are respectively given by [23]…”

“…Macorra [22] studied the cosmological evolution of two coupled scalar fields with an arbitrary interaction term and discussed the possibility of having one of the scalar fields as of dark energy while the other could be a scalar field redshifting as matter. An interaction between phantom field and tachyonic field was considered by Chattopadhyay and Debnath [23]. Motivated by the investigations on the validity of generalized second law of thermodynamics in presence of phantom field [15], holographic dark energy [17], quintom [16] and surveying the literatures on two-component models [12,18,22,23,24,25] we decided to investigate the validity of the generalized second law of thermodynamics in presence of interacting as well as non-interacting tachyonic field and scalar (phantom) field.…”

“…In an earlier work by the authors of the present work (Reference [23]), the solutions for φ1 , φ2 , V 1 , and V 2 were obtained under interaction as follows:…”

Interaction between phantom field and modified Chaplygin gas

“…where, 0 ≤ α ≤ 1 and A and B are positive constants. Now, consider that the phantom field interacting with Chaplygin gas, so the continuity equations for these two fluids can be written through the interaction term Q [18] ρ1 + 3H(ρ…”

“…The nature of the Q term is not clear at all. It may arise in principle from some microscopic mechanisms [18]. For solving these equations different forms for the interaction term Q have been considered in the literature.…”