731 citations · 1.1k across the 10 of their papers we have counts for
10 papers
The and the CDM as integration constants
Priidik Gallagher, Tomi Koivisto
Notoriously, the two main problems of the standard CDM model of cosmology are the cosmological constant and the cold dark matter, CDM. This essay shows that both the and…
Anisotropic cosmology and inflation from tilted Bianchi IX model
Peter Sundell, Tomi Koivisto
The dynamics of the tilted axisymmetric Bianchi IX cosmological models are explored allowing energy flux in the source fluid. The Einstein equations and the continuity equation are…
Atick-Witten Hagedorn Conjecture, near scale-invariant matter and blue-tilted gravity power spectrum
Tirthabir Biswas, Tomi Koivisto, Anupam Mazumdar
We will provide an interesting new mechanism to generate almost scale invariant seed density perturbations with a red spectrum, while keeping the gravitational wave spectrum blue-t…
Cosmological perturbations from statistical thermal fluctuations
Tirthabir Biswas, Robert Brandenberger, Tomi Koivisto +1
Cosmological perturbations due to statistical thermal fluctuations in a single fluid characterized by an arbitrary equation of state are computed. Formulas to predict the scalar an…
Phase transitions during Cyclic-Inflation and Non-gaussianity
Tirthabir Biswas, Tomi Koivisto, Anupam Mazumdar
Typically cold inflation with positive vacuum energy density dilutes all matter except the quan- tum fluctuations which are stretched outside the Hubble patch during inflation. How…
Nonlocal theories of gravity: the flat space propagator
Tirthabir Biswas, Tomi Koivisto, Anupam Mazumdar
It was recently found that there are classes of nonlocal gravity theories that are free of ghosts and singularities in their Newtonian limit [PRL, 108 (2012), 031101]. In these pro…
Perturbations and non-Gaussianities in three-form inflationary magnetogenesis
Federico R. Urban, Tomi K. Koivisto
We reconsider magnetogenesis in the context of three-form inflation, and its backreaction. In particular, we focus on first order perturbation theory during inflation and subsequen…
Towards singularity and ghost free theories of gravity
Tirthabir Biswas, Erik Gerwick, Tomi Koivisto +1
We present the most general covariant ghost-free gravitational action in a Minkowski vacuum. Apart from the much studied f(R) models, this includes a large class of non-local actio…
Could our Universe have begun with Negative Lambda?
Tirthabir Biswas, Tomi Koivisto, Anupam Mazumdar
In this paper we present an informal description of the Cyclic Inflation scenario which allows our universe to "start" with a negative potential energy, inflate, and then gracefull…
Towards a Resolution of the Cosmological Singularity in Non-local Higher Derivative Theories of Gravity
Tirthabir Biswas, Tomi Koivisto, Anupam Mazumdar
One of the greatest problems of standard cosmology is the Big Bang singularity. Previously it has been shown that non-local ghostfree higher-derivative modifications of Einstein gr…