29 research outputs found
A note on the stability of axionic D-term strings
We investigate the stability of a new class of BPS cosmic strings in N=1
supergravity with D-terms recently proposed by Blanco-Pillado, Dvali and Redi.
These have been conjectured to be the low energy manifestation of D-strings
that might form from tachyon condensation after D- anti-D-brane annihilation in
type IIB superstring theory. There are three one-parameter families of
cylindrically symmetric one-vortex solutions to the BPS equations (tachyonic,
axionic and hybrid). We find evidence that the zero mode in the axionic case,
or s-strings, can be excited. Its evolution leads to the decompactification of
four-dimensional spacetime at late times, with a rate that decreases with
decreasing brane tension.Comment: 6 pages, 5 figure
Perturbative Stability along the Supersymmetric Directions of the Landscape
We consider the perturbative stability of non-supersymmetric configurations
in N=1 supergravity models with a spectator sector not involved in
supersymmetry breaking. Motivated by the supergravity description of complex
structure moduli in Large Volume Compactifications of type IIB-superstrings, we
concentrate on models where the interactions are consistent with the
supersymmetric truncation of the spectator fields, and we describe their
couplings by a random ensemble of generic supergravity theories. We
characterise the mass spectrum of the spectator fields in terms of the
statistical parameters of the ensemble and the geometry of the scalar manifold.
Our results show that the non-generic couplings between the spectator and the
supersymmetry breaking sectors can stabilise all the tachyons which typically
appear in the spectator sector before including the supersymmetry breaking
effects, and we find large regions of the parameter space where the
supersymmetric sector remains stable with probability close to one. We discuss
these results about the stability of the supersymmetric sector in two
physically relevant situations: non-supersymmetric Minkowski vacua, and
slow-roll inflation driven by the supersymmetry breaking sector. For the class
of models we consider, we have reproduced the regimes in which the KKLT and
Large Volume Scenarios stabilise all supersymmetric moduli. We have also
identified a new regime in which the supersymmetric sector is stabilised at a
very robust type of dS minimum without invoking a large mass hierarchy.Comment: 44+11 pages, 10 figures, references added, minor corrections and
clarifications, added comments by the refere
F-term uplifting and moduli stabilization consistent with Kahler invariance
An important ingredient in the construction of phenomenologically viable
superstring models is the uplifting of Anti-de Sitter supersymmetric critical
points in the moduli sector to metastable Minkowski or de Sitter vacua with
broken supersymmetry. In all cases described so far, uplifting results in a
displacement of the potential minimum away from the critical point and, if the
uplifting is large, can lead to the disappearance of the minimum altogether. We
propose a variant of F-term uplifting which exactly preserves supersymmetric
critical points and shift symmetries at tree level. In spite of a direct
coupling, the moduli do not contribute to supersymmetry breaking. We analyse
the stability of the critical points in a toy one-modulus sector before and
after uplifting, and find a simple stability condition depending solely on the
amount of uplifting and not on the details of the uplifting sector. There is a
region of parameter space, corresponding to the uplifting of local AdS {\em
maxima} --or, more importantly, local minima of the Kahler function-- where the
critical points are stable for any amount of uplifting. On the other hand,
uplifting to (non- supersymmetric) Minkowski space is special in that all SUSY
critical points, that is, for all possible compactifications, become stable or
neutrally stable.Comment: 20 pages, 1 figur