Causal dissipative cosmology

The full version of the causal thermodynamics of non-equilibrium phenomena is discussed in the context of the flat Friedmann-Robertson-Walker cosmological model. Power law solutions for the scale factor are shown to exist. It is also shown that the temporal behaviour of the temperature depends on the functional dependence of the coefficient of bulk viscosity on density.     

Baryogenesis and the new cosmology

I begin this talk with a brief review of the status of approaches to understanding the origin of the baryon asymmetry of the Universe (BAU). I then describe a recent model unifying three seemingly distinct problems facing particle cosmology: the origin of inflation, the generation of the BAU and the nature of dark energy.     

Summary of cosmology workshop

Cosmology is passing through a golden phase of rapid advance. The cosmology workshop at ICGC-2004 attracted a large number of research contributions to diverse topics of cosmology. I attempt to classify and summarize the research work and results of the oral and poster presentations made at the meeting.     

The current status of observational cosmology

Observational cosmology has indeed made very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation. The transition to precision cosmology has been spear-headed by measurements of the anisotropy in the cosmic microwave background (CMB) over the past decade. Observations of the large scale structure in the distribution of galaxies, high red-shift supernova, have provided the required complementary information. We review the current status of cosmological parameter estimates from joint analysis of CMB anisotropy and large scale structure (LSS) data. We also sound a note of caution on overstating the successes achieved thus far.     

Noncommutative quantum cosmology

We consider noncommutative quantum cosmology in the case of the low-energy string effective theory. Exact solutions are found and compared with the commutative case.     

Accelerating cosmology in modified gravity with scalar field

The modified gravity with 1/R term (R being the scalar curvature) and the Einstein-Hilbert term is studied by incorporating the phantom scalar field. A number of cosmological solutions are derived in the presence of the phantom field in the perfect fluid background. It is shown: the current inflation obtained in the modified gravity is affected by the existence of the phantom field.     

Eternal inflation with Liouville cosmology

We present a concrete holographic realization of the eternal inflation in (1+1)$(1+1)$-dimensional Liouville gravity by applying the philosophy of the FRW/CFT correspondence proposed by Freivogel, Sekino, Susskind and Yeh (FSSY). The dual boundary theory is nothing but the old matrix model describing the two-dimensional Liouville gravity coupled with minimal model matter fields. In Liouville gravity, the flat Minkowski space or even the AdS space will decay into the dS space, which is in stark contrast with higher-dimensional theories, but the spirit of the FSSY conjecture applies with only minimal modification. We investigate the classical geometry as well as some correlation functions to support our claim. We also study an analytic continuation to the time-like Liouville theory to discuss possible applications in (1+3)$(1+3)$-dimensional cosmology along with the original FSSY conjecture, where the boundary theory involves the time-like Liouville theory. We show that the decay rate in the (1+3)$(1+3)$ dimension is more suppressed due to the quantum gravity correction of the boundary theory.     

Cosmological constant in the Bianchi type-I-modified Brans-Dicke cosmology

In 1961, Brans and Dicke [1] provided an interesting alternative to general relativity based on Mach’s principle. To understand the reasons leading to their field equations, we first consider homogeneous and isotropic cosmological models in the Brans-Dicke theory. Accordingly we start with the Robertson-Walker line element and the energy tensor of a perfect fluid. The scalar field φ is now a function of the cosmic time only. Then we consider spatially homogeneous and anisotropic Bianchi type-I-cosmological solutions of modified Brans-Dicke theory containing barotropic fluid. These have been obtained by imposing a condition on the cosmological parameter Λ(φ). Again we try to focus the meaning of this cosmological term and to relate it to the time coordinate which gives us a collapse singularity or the initial singularity. On the other hand, our solution is a generalization of the solution found by Singh and Singh [2]. As far as we are aware, such solution has not been given earlier.     

Massless particles and cosmology

Post recombination density perturbations have been studied in a two-component matter-radiation universe. The study has been carried out for variable matter and radiation densities. The possibility of the existence of different kinds of neutrinos in addition to the electronic, muonic and taonic has been considered and conclusions have been drawn as to the upper limit of the radiation density for different values of Ω _m .     

Tachyon field in cosmology

We study cosmological effects of homogeneous tachyon field as dark energy. We concentrate on two different scalar field potentials, the inverse square potential and the exponential potential. These models have a unique feature that the matter density parameter and the density parameter for tachyons remain comparable for a large range in red-shift. It is shown that there exists a range of parameters for which the universe undergoes an accelerated expansion and the evolution is consistent with structure formation requirements. For a viable model we require fine tuning of parameters comparable to that in ACDM or in quintessence models. For the exponential potential, the accelerated phase is followed by a phase witha(t) α t ^2/3 thus eliminating a future horizon.     

ROSETTA and FIRST: Two cornerstone missions of ESA long-term space science programme

Summary The paper reviews the objectives and status of definition of ROSETTA (Comet Nucleus Sample Return) and FIRST (Far Infrared Space Telescope), which are two cornerstone missions of the ESA long-term scientific programme. ROSETTA is a joint ESA/NASA programme and it will address problems centered on the origin of planetary material and the pre-biotic evolution of organic matter. The ROSETTA spacecraft will be launched in 2001; it will land into the nucleus of comet Churyumov-Gerasimenko, take about 10 kg of cometary samples (ice, dust, organics) and will return the Earth in 2008. FIRST will explore the 10 μm to 1 mm region of the electromagnetic spectrum, where a large number of very important atomic and molecular spectral lines are hosted. The major scientific objectives are the physics of the interstellar medium of the star formation and cosmological studies. The mission is based on a 4.5 to 8 m telescope equipped with imaging spectrometers and operating as a near-real-time observatory from a high elliptical orbit of 24 h period. Low operating temperatures for the payload will be achieved by using a combination of mechanical coolers and a liquid helium cryostat. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Observational effects from quantum cosmology

The status of quantum cosmologies as testable models of the early universe is assessed in the context of inflation. While traditional Wheeler–DeWitt quantization is unable to produce sizable effects in the cosmic microwave background, the more recent loop quantum cosmology can generate potentially detectable departures from the standard cosmic spectrum. Thus, present observations constrain the parameter space of the model, which could be made falsifiable by near‐future experiments.     

Neutrino physics from precision cosmology

Cosmology provides an excellent laboratory for testing various aspects of neutrino physics. Here, I review the current status of cosmological searches for neutrino mass, as well as other properties of neutrinos. Future cosmological probes of neutrino properties are also discussed in detail.     

Bulk viscous cosmology in early Universe

The effect of bulk viscosity on the early evolution of Universe for a spatially homogeneous and isotropic Robertson-Walker model is considered. Einstein’s field equations are solved by using ‘gamma-law’ equation of state p = (γ − 1)ρ, where the adiabatic parameter gamma (γ) depends on the scale factor of the model. The ‘gamma’ function is defined in such a way that it describes a unified solution of early evolution of the Universe for inflationary and radiation-dominated phases. The fluid has only bulk viscous term and the coefficient of bulk viscosity is taken to be proportional to some power function of the energy density. The complete general solutions have been given through three cases. For flat space, power-law as well as exponential solutions are found. The problem of how the introduction of viscosity affects the appearance of singularity, is briefly discussed in particular solutions. The deceleration parameter has a freedom to vary with the scale factor of the model, which describes the accelerating expansion of the Universe.      

Classical stochastic approach to cosmology revisited

The classical stochastic model of cosmology recently developed by us is reconsidered. In that approach the parameterw defined by the equation of statep = wp was taken to be fluctuating with mean zero and we compared the theoretical probability distribution function (PDF) for the Hubble parameter with observational data corresponding to a universe with matter and vacuum energy. Even though qualitative agreement between the two was obtained, an attempt is herein made to introduce a more realistic assumption for the mean ofw and use it for the calculations. In the present theory the mean values of bothp andw are taken to be nonzero. The theoretical and observational PDFs are compared for different epochs and values of the Hubble parameter. The corresponding values of the diffusion constantD obtained are approximately constant. We use the scatter in the observed redshift-magnitude data of Type Ia supernova to place limits on the stochastic variation in expansion rate and consequently, on the stochastic variation of the equation of state.     

Observational constraints on loop quantum cosmology

In the inflationary scenario of loop quantum cosmology in the presence of inverse-volume corrections, we give analytic formulas for the power spectra of scalar and tensor perturbations convenient to compare with observations. Since inverse-volume corrections can provide strong contributions to the running spectral indices, inclusion of terms higher than the second-order runnings in the power spectra is crucially important. Using the recent data of cosmic microwave background and other cosmological experiments, we place bounds on the quantum corrections.     

Anisotropic Lyra cosmology

Anisotropic Bianchi Type-I cosmological models have been studied on the basis of Lyra’s geometry. Two types of models, one with constant deceleration parameter and the other with variable deceleration parameter have been derived by considering a time-dependent displacement field.     

Reparameterization invariants for anisotropic Bianchi I cosmology with a massless scalar source

Intrinsic time-dependent invariants are constructed for classical, flat, homogeneous, anisotropic cosmology with a massless scalar material source. Invariance under the time reparameterization-induced canonical symmetry group is displayed explicitly.