Evolution of perturbations in a domain wall cosmology

Abstract

A fluid of domain walls may have an effective equation of state p w = − 2 3 ρ w . This equation of state is qualitatively in agreement with the supernova type Ia observations. We exploit a cosmological model where the matter content is given by a dust fluid and a domain wall fluid. The process of formation of galaxies is essentially preserved. On the other hand, the behaviour of the density contrast in the ordinary fluid is highly altered when domain walls begin to dominate the matter content of the Universe. This domain wall phase occurs at relative recent era, and its possible consequences are discussed, specially concerning the Sachs-Wolfe effect.One of the most surprising observational results in cosmology in the end of this century is due to the use of the Supernova type Ia as standard candles in the evaluation of luminosity distance as function of the redshift z. The two groups consecrated to this program [1,2] arrived at the same conclusion: the Universe is now in an accelerated phase. The inflationary paradigm, initially restricted to the very early Universe, was transferred to the Universe today with strinking consequences, for example, for the age of the Universe and many other cosmological parameters [3,4]. The most accepted results [5] indicate that the value of the decelerating parameter today is given by q = −ä Hence, the Universe today should be dominated by a fluid with negative pressure such that the strong energy condition is violated.One of the main issues related to this observational results, is the nature of this negative pressure fluid. The position of the first acoustic peak in the spectrum of the anisotropy of cosmic microwave background radiation is related to the total density of the Universe. In spite of the fact that there is not until now doubtless observational results indicating where precisely this first acoustic peak is located, the recent data coming from BOOMERANG and MAXIMA projects indicate that the density of the Universe is near the critical density [6,7]. Hence, it can be assumed that the Universe is spatially or nearly spatially flat. On the other hand, the clustered mass is responsable for 0.3 ∼ 0.4 of the critical density. Consequently, from this data it is possible to conclude that 0.7 ∼ 0.6 of the total matter of the Universe is a smooth component which is generally called dark energy.A fluid of negative pressure violating the strong energy condition does not cluster at large scale. In particular, a cosmological constant, which can be represented by an equation of state p = −ρ, remains perfectly smooth, since its density fluctuations are exactly zero. However, the above mentioned results for the deceleration parameter suggest a fluid different from the cosmological constant. A very popular model to describe this dark energy is the so-called "quintessence", a scalar field with an appropriate potential term such that the effective equation of state evolves from a typical radiation equation of state (p = ρ 3 ) to a negative equation of state [8][9][10][11]. But, it is d...

Late universe expansion dominated by domain walls and dissipative dark matter

“…This solves the coincidence problem that afflicts many approaches to late acceleration without recourse to fine tuning. Domain walls are ubiquitous in field theory models with spontaneously broken discrete symmetries [17] and they appear to be compatible with the observations of large scale structure [18], and the CMB anisotropy spectrum provided that the domain walls network is strongly frustrated [13]. In such a case its equation of state parameter w = p dw /ρ dw may vary with expansion according to…”

Noncanonical Domain Wall as a Unified Model of Dark Energy and Dark Matter: I. Cosmic Dynamics 1,2

“…Therefore, a noncanonical domain wall occupying its quantum ground state is a domain wall with Lagrangian (2.3) that physically does not suffer from quantum instability. In the canonical formalism, a domain wall with zero velocity is called a frustrated domain wall [17,18,20,21]. However, in the noncanonical formalism, for distinction and brevity, we call it a freezing domain wall.…”

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Quantum Cosmology with Many Fluids and the Choice of Cosmological Time

“…In terms of hydrodynamical description the domain walls fluid is represented by the particular equation of state p dw = − 2 3 ρ dw . This type of fluid is also known as solid dark energy, which possesses resistance to pure shear deformations, guaranteeing stability with respect to small perturbations [24]. The microphysical origin for solid dark energy is a dense network of low-tension domain walls.…”