581 research outputs found
The energy and stability of D-term strings
Cosmic strings derived from string theory, supergravity or any theory of
choice should be stable if we hope to observe them. In this paper we consider
D-term strings in D=4, N=1 supergravity with a constant Fayet-Iliopoulos term.
We show that the positive deficit angle supersymmetric D-term string is
non-perturbatively stable by using standard Witten-Nester techniques to prove a
positive energy theorem. Particular attention is paid to the negative deficit
angle D-term string, which is known to violate the dominant energy condition.
Within the class of string solutions we consider, this violation implies that
the negative deficit angle D-term string must have a naked pathology and
therefore the positive energy theorem we prove does not apply to it. As an
interesting aside, we show that the Witten-Nester charge calculates the total
gravitational energy of the D-term string without the need for a cut-off, which
may not have been expected.Comment: 18 pages. v2: minor changes and references adde
From ten to four and back again: how to generalize the geometry
We discuss the four-dimensional N=1 effective approach in the study of warped
type II flux compactifications with SU(3)x SU(3)-structure to AdS_4 or flat
Minkowski space-time. The non-trivial warping makes it natural to use a
supergravity formulation invariant under local complexified Weyl
transformations. We obtain the classical superpotential from a standard
argument involving domain walls and generalized calibrations and show how the
resulting F-flatness and D-flatness equations exactly reproduce the full
ten-dimensional supersymmetry equations. Furthermore, we consider the effect of
non-perturbative corrections to this superpotential arising from gaugino
condensation or Euclidean D-brane instantons. For the latter we derive the
supersymmetry conditions in N=1 flux vacua in full generality. We find that the
non-perturbative corrections induce a quantum deformation of the internal
generalized geometry. Smeared instantons allow to understand KKLT-like AdS
vacua from a ten-dimensional point of view. On the other hand, non-smeared
instantons in IIB warped Calabi-Yau compactifications 'destabilize' the
Calabi-Yau complex structure into a genuine generalized complex one. This
deformation gives a geometrical explanation of the non-trivial superpotential
for mobile D3-branes induced by the non-perturbative corrections.Comment: LaTeX, 47 pages, v2, references, hyperref added, v3, correcting small
inaccuracies in eqs. (2.6a) and (5.16
D-branes on AdS flux compactifications
We study D-branes in N=1 flux compactifications to AdS_4. We derive their
supersymmetry conditions and express them in terms of background generalized
calibrations. Basically because AdS has a boundary, the analysis of stability
is more subtle and qualitatively different from the usual case of Minkowski
compactifications. For instance, stable D-branes filling AdS_4 may wrap trivial
internal cycles. Our analysis gives a geometric realization of the
four-dimensional field theory approach of Freedman and collaborators.
Furthermore, the one-to-one correspondence between the supersymmetry conditions
of the background and the existence of generalized calibrations for D-branes is
clarified and extended to any supersymmetric flux background that admits a
time-like Killing vector and for which all fields are time-independent with
respect to the associated time. As explicit examples, we discuss supersymmetric
D-branes on IIA nearly Kaehler AdS_4 flux compactifications.Comment: 43 pages, 2 pictures, 1 table; v2: added references, color to figure
and corrected typo in (6.21b
Wilson Loop, Regge Trajectory and Hadron Masses in a Yang-Mills Theory from Semiclassical Strings
We compute the one-loop string corrections to the Wilson loop, glueball Regge
trajectory and stringy hadron masses in the Witten model of non supersymmetric,
large-N Yang-Mills theory. The classical string configurations corresponding to
the above field theory objects are respectively: open straight strings, folded
closed spinning strings, and strings orbiting in the internal part of the
supergravity background. For the rectangular Wilson loop we show that besides
the standard Luescher term, string corrections provide a rescaling of the field
theory string tension. The one-loop corrections to the linear glueball Regge
trajectories render them nonlinear with a positive intercept, as in the
experimental soft Pomeron trajectory. Strings orbiting in the internal space
predict a spectrum of hadronic-like states charged under global flavor
symmetries which falls in the same universality class of other confining
models.Comment: 52 pages, latex 3 times, v3: references adde
Perturbing gauge/gravity duals by a Romans mass
We show how to produce algorithmically gravity solutions in massive IIA (as
infinitesimal first order perturbations in the Romans mass parameter) dual to
assigned conformal field theories. We illustrate the procedure on a family of
Chern--Simons--matter conformal field theories that we recently obtained from
the N=6 theory by waiving the condition that the levels sum up to zero.Comment: 30 page
D-branes on general N=1 backgrounds: superpotentials and D-terms
We study the dynamics governing space-time filling D-branes on Type II flux
backgrounds preserving four-dimensional N=1 supersymmetry. The four-dimensional
superpotentials and D-terms are derived. The analysis is kept on completely
general grounds thanks to the use of recently proposed generalized
calibrations, which also allow one to show the direct link of the
superpotentials and D-terms with BPS domain walls and cosmic strings
respectively. In particular, our D-brane setting reproduces the tension of
D-term strings found from purely four-dimensional analysis. The holomorphicity
of the superpotentials is also studied and a moment map associated to the
D-terms is proposed. Among different examples, we discuss an application to the
study of D7-branes on SU(3)-structure backgrounds, which reproduces and
generalizes some previous results.Comment: 50 pages; v2: table of contents, some clarifications and references
added; v3: typos corrected and references adde
Supersymmetric D-branes and calibrations on general N=1 backgrounds
We study the conditions to have supersymmetric D-branes on general {\cal N}=1
backgrounds with Ramond-Ramond fluxes. These conditions can be written in terms
of the two pure spinors associated to the SU(3)\times SU(3) structure on
T_M\oplus T^\star_M, and can be split into two parts each involving a different
pure spinor. The first involves the integrable pure spinor and requires the
D-brane to wrap a generalised complex submanifold with respect to the
generalised complex structure associated to it. The second contains the
non-integrable pure spinor and is related to the stability of the brane. The
two conditions can be rephrased as a generalised calibration condition for the
brane. The results preserve the generalised mirror symmetry relating the type
IIA and IIB backgrounds considered, giving further evidence for this duality.Comment: 23 pages. Some improvements and clarifications, typos corrected and
references added. v3: Version published in JHE
The general (2,2) gauged sigma model with three--form flux
We find the conditions under which a Riemannian manifold equipped with a
closed three-form and a vector field define an on--shell N=(2,2) supersymmetric
gauged sigma model. The conditions are that the manifold admits a twisted
generalized Kaehler structure, that the vector field preserves this structure,
and that a so--called generalized moment map exists for it. By a theorem in
generalized complex geometry, these conditions imply that the quotient is again
a twisted generalized Kaehler manifold; this is in perfect agreement with
expectations from the renormalization group flow. This method can produce new
N=(2,2) models with NS flux, extending the usual Kaehler quotient construction
based on Kaehler gauged sigma models.Comment: 24 pages. v2: typos fixed, other minor correction
- …