Related papers: Semi-local Cosmic Strings and the Cosmological Con…
Progress on string theory in curved spacetimes since 1992 are reviewed. After a short introduction on strings in Minkowski and curved spacetimes, we focus on strings in cosmological spacetimes. The classical behaviour of strings in FRW and…
A solution of the vortex type is given in a six-dimensional $SU(2)\times U(1)$ pure gauge theory coupled to Einstein gravity in a compactified background geometry. We construct the solution of an effective abelian Higgs model in terms of…
We present a manifestly local and general coordinate invariant formulation of a nonlocal approach to the cosmological constant problem which has been recently proposed by Carroll and Remmen. To do that, we need to introduce a topological…
Non-Abelian strings for an Einstein-Yang-Mills-Higgs theory are explicitly constructed. We consider N_f Higgs fields in the fundamental representation of the U(1)xSU(N_c) gauge group in order to have a color-flavor SU(N_c) group remaining…
We study cosmic strings in the complex symmetron model, a scalar-tensor theory with a spontaneously broken local $U(1)$ symmetry in low matter density regions. Using numerical simulations, we show that these strings preferentially attach to…
A five-dimensional solution to Einstein's equations coupled to a scalar field has been proposed as a partial solution to the cosmological constant problem: the effect of arbitrary vacuum energy (tension) of a 3-brane is cancelled; however,…
In N=1 supergravity the scalar potential of the hidden sector may have degenerate supersymmetric (SUSY) and non-supersymmetric Minkowski vacua. In this case local SUSY in the second supersymmetric Minkowski phase can be broken dynamically.…
A mechanism for suppressing the cosmological constant is developed, based on an analogy with a superconducting phaseshift in which free fermions coupled perturbatively to a weak gravitational field are in an unstable false vacuum state. The…
We investigate the standard model in a cosmic string background and show that the electroweak symmetry is partially restored. For a range of parameters the electroweak Higgs field can wind in this region, producing an electroweak string…
In supergravity models, the quantum correction to the vacuum energy can be of order $M_I^4$, if the cutoff is of order the Planck mass $M^2_{P}$ and $Str\ {\cal M}^2\ne 0$. Therefore, the tree level cosmological constant must be nonzero…
Semilocal and electroweak strings are well-known to be unstable against unwinding by the condensation of the second Higgs component in their cores. A large class of current models of dark matter contains dark scalar fields coupled to the…
We present the formation of metastable cosmic strings (CSs) in the context of a supersymmetric (SUSY) left-right model. The SU(2)R symmetry breaking occurs during a stage of T-model (Higgs) inflation (TI) driven by an SU(2)R triplet…
We study brane-world solutions of five-dimensional supergravity in singular spaces. We exhibit a self-tuned four-dimensional cosmological constant when five-dimensional supergravity is broken by an arbitrary tension on the brane-world. The…
The main goal of this work is to pursue an investigation of cosmic string configurations focusing on possible consequences of the Lorentz-symmetry breaking by a background vector. We analyze the possibility of cosmic strings as a viable…
Phenomenologically viable string vacua may require incorporating Kac-Moody algebras at level $\geq 2$. We exploit the free fermionic formulation to construct N=(0,2) world-sheet supersymmetric string models with specific phenomenological…
Within a slightly simplified version of the electroweak standard model we investigate the stabilization of cosmic strings by fermion quantum fluctuations. Previous studies of quantum energies considered variants of the Nielsen-Olesen…
Motivated by recent work of Bousso and Polchinski (BP), we study theories which explain the small value of the cosmological constant using the anthropic principle. We argue that simultaneous solution of the gauge hierarchy problem is a…
The region of moduli space of string theories which is most likely to describe the "real world" is where the string coupling is about unity and the volume of extra compact dimensions is about the same size as the string volume. Here we map…
Some of the soft SUSY breaking parameters in hidden sector supergravity model depend on the expectation value of the hidden sector scalar potential, $<V_h>$, whose tree level value is equal to the tree level cosmological constant. The…
A mechanism for suppressing the cosmological constant is described, using a superconducting analogy in which fermions coupled to gravitons are in an unstable false vauum. The coupling of the fermions to gravitons and a screened attractive…