Reconstructing the evolution of dark energy with variations of fundamental parameters (2009)
Nunes, N. J., Dent, T., Robbers, G.
Under the assumption that the variations of parameters of nature and the current acceleration of the universe are related and governed by the evolution of a single scalar field, we show how...
Non-linear non-local Cosmology (2008)
Non-local equations of motion contain an infinite number of derivatives and commonly appear in a number of string theory models. We review how these equations can be rewritten in the form of a...
The gravitational wave background from super-inflation in Loop Quantum Cosmology (2008)
Copeland, E. J., Mulryne, D. J., Nunes, N. J., Shaeri, M.
We investigate the behaviour of tensor fluctuations in Loop Quantum Cosmology, focusing on a class of scaling solutions which admit a near scale-invariant scalar field power spectrum. We obtain the...
Moduli evolution in the presence of thermal corrections (2008)
Barreiro, T., De Carlos, B., Copeland, E.J., Nunes, N.J.
We study the effect of thermal corrections on the evolution of moduli in effective Supergravity models. This is motivated by previous results in the literature suggesting that these corrections could...
Aghanim, N., Da Silva, A. C., Nunes, N. J.
Clusters are potentially powerful tools for cosmology provided their observed properties such as the Sunyaev-Zel'dovich (SZ) or X-ray signals can be translated into physical quantities like mass and...
Diffusing non-local inflation: Solving the field equations as an initial value problem (2008)
There has been considerable recent interest in solving non-local equations of motion which contain an infinite number of derivatives. Here, focusing on inflation, we review how the problem can be...
Moduli evolution in the presence of thermal corrections (2007)
Barreiro, T., De Carlos, B., Copeland, E. J., Nunes, N. J.
We study the effect of thermal corrections on the evolution of moduli in effective Supergravity models. This is motivated by previous results in the literature suggesting that these corrections could...
Primordial Density Fluctuations in a Dual Supergravity Cosmology (2007)
Bento Bertolami, M. C. Bento, O. Bertolami, N. J. Nunes
We analyse the spectrum of energy density fluctuations of a dual supergravity model where the dilaton and the moduli are stabilized and sucessful inflation is achieved inside domain walls that...
Super-inflation in Loop Quantum Cosmology (2007)
Copeland, E. J., Mulryne, D. J., Nunes, N. J., Shaeri, M.
We investigate the dynamics of super-inflation in two versions of Loop Quantum Cosmology, one in which the Friedmann equation is modified by the presence of inverse volume corrections, and one in...
Dynamics of Logamediate Inflation (2007)
A computation of the inflationary observables n_{s} and r is made for `logamediate' inflation where the cosmological scale factor expands as $a=\exp (A(\ln t)^{\lambda})$, and is compared to their...
Measurements of Omega and Lambda from 42 High-Redshift Supernovae (2007)
Perlmutter, S., Aldering, G., Goldhaber, G., Knop, R. A., Nugent, P., Castro, P. G., ...
We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova...
Coupled Variations of Fundamental Couplings and Primordial Nucleosynthesis (2007)
Coc, A., Nunes, N.J., Olive, K.A., Vangioni, E.
The effect of variations of the fundamental nuclear parameters on big-bang nucleosynthesis are modeled and discussed in detail taking into account the interrelations between the fundamental...
Constraints on a scale invariant power spectrum from superinflation in LQC (2006)
The computation of the spectrum of primordial perturbations, generated by a scalar field during the super-inflationary phase of Loop Quantum Cosmology, is revisited. The calculation is performed for...
Reconstructing the dark energy equation of state with varying couplings (2006)
Avelino, P. P., Nunes, N. J., Olive, K. A.
We revisit the idea of using varying couplings to probe the nature of dark energy, in particular by reconstructing its equation of state. We show that this method can be far superior to the standard...
Inflation: A graceful entrance from Loop Quantum Cosmology (2005)
The evolution of a scalar field is explored taking into account the presence of a background fluid in a positively curved Universe in the framework of loop quantum cosmology. Though the mechanism...
Moduli evolution in the presence of flux compactifications (2005)
Barreiro, T., De Carlos, B., Copeland, E. J., Nunes, N. J.
We study the cosmological evolution of the volume moduli in a class of recently proposed Inflationary Universe models arising out of Type IIB string theory, where a number of the moduli fields have...
On the stability of field-theoretical regularizations of negative tension branes (2005)
Any attempt to regularize a negative tension brane through a bulk scalar requires that this field is a ghost. One can try to improve in this aspect in a number of ways. For instance, it has been...
Number counts in homogeneous and inhomogeneous dark energy models (2005)
Nunes, N. J., Da Silva, A. C., Aghanim, N.
In the simple case of a constant equation of state, redshift distribution of collapsed structures may constrain dark energy models. Different dark energy models having the same energy density today...
Inflationary Cosmology and Oscillating Universes in Loop Quantum Cosmology (2004)
Mulryne, D. J., Nunes, N. J., Tavakol, R., Lidsey, J. E.
We study oscillatory universes within the context of Loop Quantum Cosmology. We make a comparative study of flat and positively curved universes sourced by scalar fields with either positive or...
Structure Formation in Inhomogeneous Dark Energy Models (2004)
We investigate how inhomogeneous quintessence models may have a specific signature even in the linear regime of large scale structure formation. The dynamics of the collapse of a dark matter halo is...
Oscillatory Universes in Loop Quantum Cosmology and Initial Conditions for Inflation (2004)
Lidsey, James E., Mulryne, David J., Nunes, N. J., Tavakol, Reza
Positively-curved, oscillatory universes are studied within the context of Loop Quantum Cosmology subject to a consistent semi-classical treatment. The semi-classical effects are reformulated in...
Reconstructing the dark energy equation of state with varying alpha (2003)
Nunes, N. J., Lidsey, James E.
The possibility of reconstructing the dark energy equation of state from variations in the fine structure constant is investigated for a class of models where the quintessence field is non-minimally...
Copeland, E. J., Nunes, N. J., Pospelov, M.
We study the change of the effective fine structure constant in the cosmological models of a scalar field with a non-vanishing coupling to the electromagnetic field. Combining cosmological data and...
Inflation in Gauss-Bonnet Brane Cosmology (2003)
Lidsey, James E., Nunes, N. J.
The effect of including a Gauss-Bonnet contribution in the bulk action is investigated within the context of the steep inflationary scenario. When inflation is driven by an exponential inflaton...
Tracking quintessential inflation from brane worlds (2002)
We analyse the mechanism of quintessential inflation in brane world scenarios for a number of particle physics inspired scalar potentials. We constrain the parameter space of those scalar potentials...
Applications of scalar attractor solutions to Cosmology (2001)
Ng, S. C. C., Nunes, N. J., Rosati, F.
We develop a framework to study the phase space of a system consisting of a scalar field rolling down an arbitrary potential with varying slope and a background fluid, in a cosmological setting. We...
Moduli Evolution in Heterotic Scenarios (2000)
Barreiro, T, De Carlos, B, Nunes, N J
We discuss several aspects of the cosmological evolution of moduli fields in heterotic string/M-theory scenarios. In particular we study the equations of motion of both the dilaton and overall...
Moduli Evolution in Heterotic Scenarios (2000)
Barreiro, T., De Carlos, B., Nunes, N. J.
We discuss several aspects of the cosmological evolution of moduli fields in heterotic string/M-theory scenarios. In particular we study the equations of motion of both the dilaton and overall...
Quintessence models in Supergravity (2000)
Copeland, E. J., Nunes, N. J., Rosati, F.
Scalar field models of quintessence typically require that the expectation value of the field today is of order the Planck mass, if we want them to explain the observed acceleration of the Universe....
Quintessence arising from exponential potentials (1999)
Barreiro, T., Copeland, E. J., Nunes, N. J.
We demonstrate how exponential potentials that could arise in the early Universe as a result of Kaluza-Klein type compactifications of string theory, can lead to cosmological solutions which...
Generalized Assisted Inflation (1999)
Copeland, E. J., Mazumdar, Anupam, Nunes, N. J.
We obtain a new class of exact cosmological solutions for multi-scalar fields with exponential potentials. We generalize the assisted inflation solutions previously obtained, and demonstrate how they...
Measurements Of Omega and Lambda from 42 High-Redshift Supernovae (1999)
G. Aldering, G. Goldhaber, R.A. Knop, P. Nugent, P. G. Castro, ...
We report measurements of the mass density,\Omega M , and cosmological-constant energy density,\Omega , of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova...
Measurements of Omega and Lambda from 42 High-Redshift Supernovae (1998)
Perlmutter, S., Aldering, G., Goldhaber, G., Knop, R. A., Nugent, P., Castro, P. G., ...
We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova...
Primordial Density Fluctuations in a Dual Supergravity Cosmology (1998)
Bento, M. C., Bertolami, O., Nunes, N. J.
We analyse the spectrum of energy density fluctuations of a dual supergravity model where the dilaton and the moduli are stabilized and sucessful inflation is achieved inside domain walls that...