C.J.A.P. Martins

Extending the velocity-dependent one-scale string evolution model

We provide a general overview of the velocity-dependent one-scale model for cosmic string evolution and discuss two further extensions to it. We introduce and justify a new ansatz for the momentum parameter k, and also incorporate the effect of radiation back reaction. We thus discuss the evolution of the basic large-scale features of cosmic string networks in all relevant cosmological scenarios, concentrating in particular on the ``scaling solutions relevant for each case. In a companion paper, we show, by comparing with numerical simulations, that this model provides an accurate description of the large-scale features of cosmic string networks.

Cosmological consequences of the brane/bulk interaction

Abstract We investigate cosmological consequences arising from the interaction between a homogeneous and isotropic brane-universe and the bulk. A Friedmann equation is derived which incorporates both the brane and bulk matter contributions, which are both assumed to be of arbitrary fluid form. In particular, new terms arise which describe the energy flow onto (or away from) the brane, as well as changes of the equation of state in the bulk. We discuss Randall–Sundrum type models as well as dilatonic domain walls and carefully consider the conditions for stabilizing the induced gravitational constant. Furthermore, consequences for cosmological perturbations are analyzed. We show that, in general, super-horizon amplitudes are not constant.

Looking for a varying alpha in the cosmic microwave background

We perform a likelihood analysis of the recently released BOOMERanG and MAXIMA data, allowing for the possibility of a time-varying fine-structure constant. We find that in general this data prefers a value of

An observational determination of the proton to electron mass ratio in the early Universe

alpha

Does a varying speed of light solve the cosmological problems

that was smaller in the past (which is in agreement with measurements of

Understanding domain wall network evolution

alpha

New constraints on variations of the fine structure constant from CMB anisotropies

from quasar observations). However, there are some interesting degeneracies in the problem which imply that strong statements about

Cosmology with varying constants

alpha

VSL theories and the Doppler peak

can not be made using this method until independent accurate determinations of

Limits on cosmic chiral vortons

Omega_b h^2