74 research outputs found
On the effective action of stable non-BPS branes
We study the world-volume effective action of stable non-BPS branes present
in Type II theories compactified on K3. In particular, by exploiting the
conformal description of these objects available in the orbifold limit, we
argue that their world-volume effective theory can be chiral. The resulting
anomalies are cancelled through the usual inflow mechanism provided there are
anomalous couplings, similar to those of BPS branes, to the twisted R-R fields.
We also show that this result is in agreement with the conjectured
interpretation of these non-BPS configurations as BPS branes wrapped on
non-supersymmetric cycles of the K3.Comment: 12 pages, LaTex, no figure
Thermodynamics of vortex lines in layered superconductors
We study the dissipative thermodynamics of vortex lines in layered
superconductors within a simple string model in the dilute limit of negligible
vortex interactions and compute the specific heat in presence of
arbitrary dissipation. The interplay of dissipation, inertia and elasticity is
shown to control the qualitative thermodynamical behavior and their relative
amount determines two very distinct regimes for the specific heat. In the
dissipation dominated case we find a behavior for a large
interval of temperature below .Comment: 10 pages, RevTe
Gauge and gravitational anomalies in D=4 N=1 orientifolds
The cancellation of U(1)-gauge and U(1)-gravitational anomalies in certain
D=4 N=1 Type IIB orientifolds is analyzed in detail, from a string theory point
of view. We verify the proposal that these anomalies are cancelled by a
Green-Schwarz mechanism involving only twisted Ramond-Ramond fields. By
factorizing one-loop partition functions, we also get the anomalous couplings
of D-branes, O-planes and orbifold fixed-points to these twisted fields.
Twisted sectors with fixed-planes participate to the inflow mechanism in a
peculiar way.Comment: 21 pages, JHEP LaTex, no figures; minor corrections and reference
adde
Anomaly inflow and RR anomalous couplings
We review the anomaly inflow mechanism on D-branes and O-planes. In
particular, we compute the one-loop world-volume anomalies and derive the RR
anomalous couplings required for their cancellation.Comment: 9 pages, LaTex, Talk given by C.A. Scrucca at TMR meeting "Quantum
aspects of gauge theories, supersymmetry and unification", ENS, Paris, 1-7
September 199
On string models with Scherk-Schwarz supersymmetry breaking
We construct a general class of chiral four-dimensional string models with
Scherk--Schwarz supersymmetry breaking, involving freely acting orbifolds. The
basic ingredient is to combine an ordinary supersymmetry-preserving Z_N
projection with a supersymmetry-breaking projection Z_M' acting freely on a
subspace of the internal manifold. A crucial condition is that any generator of
the full orbifold group Z_N x Z_M' must either preserve some supersymmetry or
act freely in order to become irrelevant in some large volume limit. Tachyons
are found to be absent or limited to a given region of the tree-level moduli
space. We find several new models with orthogonal supersymmetries preserved at
distinct fixed-points. Particular attention is devoted to an interesting Z_3 x
Z_3' heterotic example.Comment: v2: Minor corrections and a reference added; v3: Title and abstract
slightly changed, figure 2 corrected and a reference adde
Metastable supersymmetry breaking in N=2 non-linear sigma-models
We perform a general study of the issue of metastability for
supersymmetry-breaking vacua in theories with N=1 and N=2 global supersymmetry.
This problem turns out to capture all the important qualitative features of the
corresponding question in theories with local supersymmetry, where
gravitational effects induce only quantitative modifications. Moreover, it
allows to directly compare the conditions arising in the N=1 and N=2 cases,
since the latter becomes particular case of the former in the rigid limit. Our
strategy consists in a systematic investigation of the danger of instability
coming from the sGoldstini scalars, whose masses are entirely due to
supersymmetry breaking mass-splitting effects. We start by reviewing the
metastability conditions arising in general N=1 non-linear sigma-models with
chiral and vector multiplets. We then turn to the case of general N=2
non-linear sigma-models with hyper and vector multiplets. We first reproduce
and clarify the known no-go theorems applying to theories with only Abelian
vector multiplets and only hyper multiplets, and then derive new results
applying to more general cases. To make the comparison with N=1 models as clear
as possible, we rely on a formulation of N=2 models where one of the
supersymmetries is manifestly realized in terms of ordinary superfields,
whereas the other is realized through non-trivial transformations. We give a
self-contained account of such a construction of N=2 theories in N=1
superspace, generalizing previous work on various aspects to reach a general
and coordinate-covariant construction. We also present a direct computation of
the supertrace of the mass matrix.Comment: 50 pages, no figures; v2 minor corrections and addition of comments
and reference
Scalar masses in general N=2 gauged supergravity theories
We readdress the question of whether any universal upper bound exists on the
square mass m^2 of the lightest scalar around a supersymmetry breaking vacuum
in generic N=2 gauged supergravity theories for a given gravitino mass m_3/2
and cosmological constant V. We review the known bounds which apply to theories
with restricted matter content from a new perspective. We then extend these
results to theories with both hyper and vector multiplets and a gauging
involving only one generator, for which we show that such a bound exists for
both V>0 and V<0. We finally argue that there is no bound for the same theories
with a gauging involving two or more generators. These results imply that in
N=2 supergravity theories metastable de Sitter vacua with V<<m^2_3/2 can only
arise if at least two isometries are gauged, while those with V>>m^2_3/2 can
also arise when a single isometry is gauged.Comment: 19 pages, 1 figure; v2 minor corrections and addition
Simple metastable de Sitter vacua in N=2 gauged supergravity
We construct a simple class of N=2 gauged supergravity theories that admit
metastable de Sitter vacua, generalizing the recent work done in the context of
rigid supersymmetry. The setup involves one hypermultiplet and one vector
multiplet spanning suitably curved quaternionic-Kahler and special-Kahler
geometries, with an Abelian gauging based on a single triholomorphic isometry,
but neither Fayet-Iliopoulos terms nor non-Abelian gauge symmetries. We
construct the most general model of this type and show that in such a situation
the possibility of achieving metastable supersymmetry breaking vacua crucially
depends on the value of the cosmological constant V relative to the gravitino
mass squared m_{3/2}^2 in Planck units. In particular, focusing on de Sitter
vacua with positive V, we show that metastability is only possible when V >=
2.17 m_{3/2}^2. We also derive an upper bound on the lightest scalar mass in
this kind of model relative to the gravitino mass m_{3/2} as a function of the
cosmological constant V, and discuss its physical implications.Comment: 26 pages, 2 figures; v2 minor corrections, some additional comments
and one reference adde
Metastable spontaneous breaking of N=2 supersymmetry
We show that contrary to the common lore it is possible to spontaneously
break N=2 supersymmetry even in simple theories without constant
Fayet-Iliopoulos terms. We consider the most general N=2 supersymmetric theory
with one hypermultiplet and one vector multiplet without Fayet-Iliopoulos
terms, and show that metastable supersymmetry breaking vacua can arise if both
the hyper-Kahler and the special-Kahler geometries are suitably curved. We then
also prove that while all the scalars can be massive, the lightest one is
always lighter than the vector boson. Finally, we argue that these results also
directly imply that metastable de Sitter vacua can exist in N=2 supergravity
theories with Abelian gaugings and no Fayet-Iliopoulos terms, again contrary to
common lore, at least if the cosmological constant is sufficiently large.Comment: 16 pages, no figures; v2 improved introduction and conclusions; v3
minor correction
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