arXiv subjects

Adam Moss

Publications and source records attributed to Adam Moss.

77 records · Page 5Linked to original sources

arXiv2007

Cosmological Perturbations in Elastic Dark Energy Models

We discuss the general framework for a perfect continuum medium in cosmology and show that an interesting generalization of the fluids normally used is for the medium to have rigidity and, hence, be analogous to an elastic solid. Such models can provide perfect, adiabatic fluids which are stable even when the pressure is negative, if the rigidity is sufficiently large, making them natural candidates to describe the dark energy. In fact, if the medium is adiabatic and isotropic, they provide the most general description of linearized perturbations. We derive the equations of motion and wave propagation speeds in the isotropic case. We point out that anisotropic models can also be incorporated within the same formalism and that they are classified by the standard Bravais Lattices. We identify the adiabatic and isocurvature modes allowed in both the scalar and vector sectors and discuss the predictions they make for CMB and matter power spectra. We comment on the relationship between these models and other fluid-based approaches to dark energy, and discuss a possible microphysical manifestation of this class of models as a continuum description of defect-dominated scenarios.

astro-ph↗

arXiv2006

Constraints on Supersymmetric Models of Hybrid Inflation

We point out that the inclusion of a string component contributing around 5% to the CMB power spectrum amplitude on large scales can increase the preferred value of the spectral index n_s of density fluctuations measured by CMB experiments. While this finding applies to any cosmological scenario involving strings, we consider in particular models of supersymmetric hybrid inflation, which predict n_s >= 0.98, in tension with the CMB data when strings are not included. Using MCMC analysis we constrain the parameter space allowed for F- and D-term inflation. For the F-term model, using minimal supergravity corrections, we find that \logκ= -2.34\pm 0.38 and M= (0.518\pm 0.059) * 10^16 GeV. The inclusion of non-minimal supergravity corrections can modify these values somewhat. In the corresponding analysis for D-term inflation, we find \logκ= -4.24\pm 0.19 and m_FI= (0.245\pm 0.031) * 10^16 GeV. Under the assumption that these models are correct, these results represent precision measurements of important parameters of a Grand Unified Theory. We consider the possible uncertainties in our measurements and additional constraints on the scenario from the stochastic background of gravitational waves produced by the strings. The best-fitting model predicts a B-mode polarization signal \approx 0.3 μK rms peaking at l \approx 1000. This is of comparable amplitude to the expected signal due to gravitational lensing of the adiabatic E-mode signal on these scales.

astro-ph↗

arXiv2006

Anisotropic perturbations due to dark energy

A variety of observational tests seem to suggest that the universe is anisotropic. This is incompatible with the standard dogma based on adiabatic, rotationally invariant perturbations. We point out that this is a consequence of the standard decomposition of the stress-energy tensor for the cosmological fluids, and that rotational invariance need not be assumed, if there is elastic rigidity in the dark energy. The dark energy required to achieve this might be provided by point symmetric domain wall network with $P/ρ=-2/3$, although the concept is more general. We illustrate this with reference to a model with cubic symmetry and discuss various aspects of the model.

astro-ph↗

arXiv2005

Elastic properties of anisotropic domain wall lattices

Interest in the elastic properties of regular lattices constructed from domain walls has recently been motivated by cosmological applications as solid dark energy. This work investigates the particularly simple examples of triangular, hexagonal and square lattices in two dimensions and a variety of more complicated lattices in three dimensions which have cubic symmetry. The relevant rigidity coefficients are computed taking into account non-affine perturbations where necessary, and these are used to evaluate the propagation velocity for any macroscopic scale perturbation mode. Using this information we assess the stability of the various configurations.

hep-th↗

arXiv2005

Constraints on the solid dark universe model

If the dark energy is modelled as a relativistic elastic solid then the standard CDM and $Λ$CDM models, as well as lattice configurations of cosmic strings or domain walls, are points in the two-dimensional parameter space $(w,c_{\rm s}^2)$. We present a detailed analysis of the best fitting cosmological parameters in this model using data from a range of observations. We find that the $χ^2$ is improved by $\sim 10$ by including the two parameters and that the $w=-1$ $Λ$CDM model is only the best fit to the data when a large number of different datasets are included. Using CMB observations alone we find that $w=-0.38\pm 0.16 $ and with the addition of Large-Scale Structure data $w=-0.62\pm 0.15 $ and $\log c_{\rm s}=-0.77\pm 0.28$. We conclude that the models based on topological defects provide a good fit to the current data, although $Λ$CDM cannot be ruled out.

astro-ph↗