Genericity of Cosmic Strings Formation in SUSY GUTs

The idea of GUT implies that the universe went through a series of phase transitions during which topological defects are expected to form. We investigate here the genericity of cosmic strings formation in realistic SUSY GUTs models. We conclude that all acceptable symmetry breaking schemes produce cosmic strings after the last inflationary phase. Generically, as they form at the end of inflation, they have a mass of order of the GUT scale. Since cosmological data coming from CMB measurements do not show evidence for such strings, they constrain GUT scale physics.Comment: 4 pages, talk at the XXXIX Rencontres de Moriond (La Thuile, March 2004), to appear in the proceeding

A Note on the evolution of cosmic string/superstring networks

In the context of brane world scenario, cosmic superstrings can be formed in D-brane annihilation at the end of the brane inflationary era. The cosmic superstring network has a scaling solution and the characteristic scale of the network is proportional to the square root of the reconnection probability.Comment: 13 pages, 12 figures (revised version

Group field theory condensate cosmology: An appetizer

This contribution is an appetizer to the relatively young and fast evolving approach to quantum cosmology based on group field theory condensate states. We summarize the main assumptions and pillars of this approach which has revealed new perspectives on the long-standing question of how to recover the continuum from discrete geometric building blocks. Among others, we give a snapshot of recent work on isotropic cosmological solutions exhibiting an accelerated expansion, a bounce where anisotropies are shown to be under control and inhomogeneities with an approximately scale-invariant power spectrum. Finally, we point to open issues in the condensate cosmology approach.Comment: Review article as an invited contribution for the special issue "Progress in Group Field Theory and Related Quantum Gravity Formalisms", Universe journa

The necessity of dark matter in MOND within galactic scales

To further test MOdified Newtonian Dynamics (MOND) on galactic scales -- originally proposed to explain the rotation curves of disk galaxies without dark matter -- we study a sample of six strong gravitational lensing early-type galaxies from the CASTLES database. To determine whether dark matter is present in these galaxies, we compare the total mass (from lensing) with the stellar mass content (from a comparison of photometry and stellar population synthesis). We find that strong gravitational lensing on galactic scales requires a significant amount of dark matter, even within MOND. On such scales a 2 eV neutrino cannot explain this excess matter -- in contrast with recent claims to explain the lensing data of the bullet cluster. The presence of dark matter is detected in regions with a higher acceleration than the characteristic MONDian scale of $\sim 10^{-10}$m/s$^2$. This is a serious challenge to MOND unless the proper treatment of lensing is qualitatively different (possibly to be developed within a consistent theory such as TeVeS)

Gravitational Effects on Domain Walls with Curvature Correction

We derive the effective action for a domain wall with small thickness in curved spacetime and show that, apart from the Nambu term, it includes a contribution proportional to the induced curvature. We then use this action to study the dynamics of a spherical thick bubble of false vacuum (de Sitter) surrounded by an infinite region of true vacuum (Schwarzschild)

Why do we live in 3+1 dimensions?

In the context of string theory we argue that higher dimensional Dp-branes unwind and evaporate so that we are left with D3-branes embedded in a (9+1)-dimensional bulk. One of these D3-branes plays the role of our Universe. Within this picture, the evaporation of the higher dimensional Dp-branes provides the entropy of our Universe.Comment: 9 pages, 4 figures. Citations added, text and figures updated to match version accepted for publicatio

Phenomenology of loop quantum cosmology

After introducing the basic ingredients of Loop Quantum Cosmology, I will briefly discuss some of its phenomenological aspects. Those can give some useful insight about the full Loop Quantum Gravity theory and provide an answer to some long-standing questions in early universe cosmology.Comment: 16 pages, 3 figures; Invited talk in the First Mediterranean Conference on Classical and Quantum Gravity (Crete, Greece

Cusps on cosmic superstrings with junctions

The existence of cusps on non-periodic strings ending on D-branes is demonstrated and the conditions, for which such cusps are generic, are derived. The dynamics of F-, D-string and FD-string junctions are investigated. It is shown that pairs of FD-string junctions, such as would form after intercommutations of F- and D-strings, generically contain cusps. This new feature of cosmic superstrings opens up the possibility of extra channels of energy loss from a string network. The phenomenology of cusps on such cosmic superstring networks is compared to that of cusps formed on networks of their field theory analogues, the standard cosmic strings.Comment: 22 pages, 5 figure

Cosmological consequences of the NonCommutative Geometry Spectral Action

Cosmological consequences of the noncommutative geometry spectral action are presented. Neglecting the nonminimal coupling of the Higgs field to the curvature, background cosmology remains unchanged, and only the inhomogeneous perturbations will evolve differently from the equivalent classical system. However, considering the nonminimal coupling, corrections will be obtained even at the level of the background cosmologies. Finally, the Higgs field may act as an inflaton field, due to its nonminimal coupling with geometry.Comment: 7 pages, LaTeX. Invited talk at the XXV Max Bonn Symposium "Physics at the Planck Scale", in Wroclaw (Poland), 29th June-3rd July 2009. To appear in the Conference Proceeding

Fundamental cosmic strings

Cosmic strings are linear concentrations of energy that may be formed at phase transitions in the very early universe. At one time they were thought to provide a possible origin for the density inhomogeneities from which galaxies eventually develop, though this idea has been ruled out, primarily by observations of the cosmic microwave background (CMB). Fundamental strings are the supposed building blocks of all matter in superstring theory or its modern version, M-theory. These two concepts were originally very far apart, but recent developments have brought them closer. The `brane-world' scenario in particular suggests the existence of macroscopic fundamental strings that could well play a role very similar to that of cosmic strings. In this paper, we outline these new developments, and also analyze recent observational evidence, and prospects for the future.Comment: Review to appear in Contemporary Physic