Related papers: From Strings Theory to the Dark Matter in Galaxies
The gravitational field of a stationary circular cosmic string loop ,externally supported against collapse, is investigated in the context of Brans-Dicke theory in the weak field approximation of the field equations. The solution is…
We study the phenomenology of superheavy decaying dark matter with mass around $10^{10}$ GeV which can arise in the low-energy limit of string compactifications. Generic features of string theory setups (such as high scale supersymmetry…
By drawing an analogy with superfluid 4He vortices we suggest that dark matter may consist of irreducibly small remnants of cosmic strings.
In this talk I review recent developments in superstring theory. In the first half of the talk I discuss some of the earlier developments in this subject. This includes a review of the status of string theory as a unified theory of gravity…
Velocity-dependent interactions in a fundamental-string dominated universe lead quite naturally, with reasonable assumptions on initial conditions, to an accelerating expanding universe without assuming the existence of a cosmological…
It is proposed that an ultra-light fermionic species, dubbed cosmic magnino has condensed into a ferromagnetic state in the Universe. The extended structure of domain walls associated with this ferromagnetism accounts for the observed Dark…
In the present work, we adopt a nonlinear scalar field theory coupled to the gravity sector to model galactic dark matter. We found analytical solutions for the scalar field coupled to gravity in the Newtonian limit, assuming an isotropic…
The dark matter constraint imposed by the recent WMAP experiment on gravitational theories is analyzed. Using the non-linearity of the vacuum Einstein's equations, it is shown that when the slow motion condition is applied to the geodesic…
In this thesis, we investigate some aspects of dark matter phenomenology and its predictive power in explaining the flattening of galaxy rotation curves at large distances. After outlining the Standard Model of particle physics, its…
We study the implications of a scalar-tensorial gravity for the metric of an isolated self-gravitating superconducting cosmic string. These modifications are induced by an arbitrary coupling of a massless scalar field to the usual tensorial…
A simple gravitational model with torsion is studied, and it is suggested that it could explain the dark matter and dark energy in the universe. It can be reinterpreted as a model using the Einstein gravitational equations where spacetime…
A radiatively stable de Sitter spacetime is constructed by considering an intrinsically non-commutative and generalized-geometric formulation of string theory, which is related to a family of F-theory models endowed with non-trivial…
Drexler dark matter is an alternate approach to dark matter that assumes that highly relativistic protons trapped in the halo of the galaxies could account for the missing mass. We look at various energetics involved in such a scenario such…
We study spherically symmetric solutions with a scalar field in the shift-symmetric subclass of the Horndeski theory. Constructing an effective energy-momentum tensor of the scalar field based on the two-fluid model, we decompose the scalar…
Dark energy is the candidate that can produce effective negative pressure and make the galaxies and galaxy clusters move away from each other in an accelerated way. The structures of the Universe have evolved from some initial primordial…
There are at least two serious moduli problems in string cosmology. The first is the possibility that moduli dominate the energy density at the time of nucleosynthesis. The second is that they may not find their minima all together. After…
The existence of "dark matter", inferred from the observed rotation curves of galaxies, is a hypothesis which is widely regarded as problematic. This paper proposes an alternative hypothesis based on the space-time geometry near a rotating…
Dark matter, believed to be present in many galaxies, is interpreted as a hydrodynamical system in interaction with the gravitational field and nothing else. An equation of state determines the mass distribution and the associated…
Observations provide increasingly strong evidence that the universe is accelerating. This revolutionary advance in cosmological observations confronts theoretical cosmology with a tremendous challenge, which it has so far failed to meet.…
An attempt is made to set constraints on the otherwise ambiguous decomposition of the rotation curves of low surface brightness galaxies into contributions due to the various components of the galaxies. For this purpose galaxies are…