290 research outputs found
A note on supersymmetric D-brane dynamics
We study the spin dependence of D-brane dynamics in the Green-Schwarz
formalism of boundary states. In particular we show how to interpret insertion
of supercharges on the boundary state as sources of non-universal spin effects
in D-brane potentials. In this way we find for a generic (D)p-brane, potentials
going like corresponding to interactions between the
different components of the D-brane supermultiplet. From the eleven dimensional
point of view, these potentials arise from the exchange of field strengths
corresponding to the graviton and the three form, coupled non-minimally to the
branes. We show how an annulus computation truncated to its massless
contribution is enough to reproduce these next-to-leading effects, meaning in
particular that the one-loop (M)atrix theory effective action should encode all
the spin dependence of low-energy supergravity interactions.Comment: LaTex file, 12 pages, no figures, some corrections in last section
and references added; version to appear in Physics Letters
Black hole - D-brane correspondence: An example
We explore the connection between D-branes and black holes in one particular
case: a -brane compactified to four dimensions on . Using the
-brane boundary state description we show the equivalence with a double
extremal N=2 black hole solution of four dimensional supergravity.Comment: 15 pages, LaTeX. Contribution by C. Nunez to the conference Quantum
Gravity in the Southern Cone, Bariloche 7-10 January 1998; to appear in the
proceeding
Oblique Corrections from Higgsless Models in Warped Space
We calculate the tree-level oblique corrections to electroweak precision
observables generated in higgless models of electroweak symmetry breaking with
a 5D SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group on a warped background. In the
absence of brane induced kinetic terms (and equal left and right gauge
couplings) we find the S parameter to be ~1.15, while T,U~0, as in technicolor
theories. Planck brane induced kinetic terms and unequal left-right couplings
can lower S, however for sufficiently low values of S tree-level unitarity will
be lost. A kinetic term localized on the TeV brane for SU(2)_D will generically
increase S, however an induced kinetic term for U(1)_{B-L} on the TeV brane
will lower S. With an appropriate choice of the value of this induced kinetic
term S~0 can be achieved. In this case the mass of the lowest Z' mode will be
lowered to about ~300 GeV.Comment: 18 pages, LaTeX, 2 figures include
Orbifold resolutions with general profile
A very general class of resolved versions of the C/Z_N, T^2/Z_N and S^1/Z_2
orbifolds is considered and the free theory of 6D chiral fermions studied on
it. As the orbifold limit is taken, localized 4D chiral massless fermions are
seen to arise at the fixed points. Their number, location and chirality is
found to be independent on the detailed profile of the resolving space and to
agree with the result of hep-th/0409229, in which a particular resolution was
employed. As a consistency check of the resolution procedure, the massive
equation is numerically studied. In particular, for S^1/Z_2, the "resolved"
mass--spectrum and wave functions in the internal space are seen to correctly
reproduce the usual orbifold ones, as the orbifold limit is taken.Comment: 28 pages, 3 figures, typos corrected, references adde
Anomalies in field theories with extra dimensions
We give an overview of the issue of anomalies in field theories with extra
dimensions. We start by reviewing in a pedagogical way the computation of the
standard perturbative gauge and gravitational anomalies on non-compact spaces,
using Fujikawa's approach and functional integral methods, and discuss the
available mechanisms for their cancellation. We then generalize these analyses
to the case of orbifold field theories with compact internal dimensions,
emphasizing the new aspects related to the presence of orbifold singularities
and discrete Wilson lines, and the new cancellation mechanisms that are
becoming available. We conclude with a very brief discussion on global and
parity anomalies.Comment: Review article written for Int.J.Mod.Phys. A, 63 pages; v2: mistake
in subsection 4.3 corrected, some comments and references added, a few
misprints fixe
Locally stable non-supersymmetric Minkowski vacua in supergravity
We perform a general study about the existence of non-supersymmetric minima with vanishing cosmological constant in supergravity models involving only chiral superfields. We study the conditions under which the matrix of second derivatives of the scalar potential is positive definite. We show that there exist very simple and strong necessary conditions for stability that constrain the Kahler curvature and the ratios of the supersymmetry-breaking auxiliary fields defining the Goldstino direction. We then derive more explicitly the implications of these constraints in the case where the Kahler potential for the supersymmetry-breaking fields is separable into a sum of terms for each of the fields. We also discuss the implications of our general results on the dynamics of moduli fields arising in string compactifications and on the relative sizes of their auxiliary fields, which are relevant for the soft terms of matter fields. We finally comment on how the idea of uplifting a supersymmetric AdS vacuum fits into our general study
Curing the Ills of Higgsless Models: the S Parameter and Unitarity
We consider various constraints on Higgsless models of electroweak symmetry
breaking based on a bulk SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group in warped
space. First we show that the S parameter which is positive if fermions are
localized on the Planck brane can be lowered (or made vanishing) by changing
the localization of the light fermions. If the wave function of the light
fermions is almost flat their coupling to the gauge boson KK modes will be
close to vanishing, and therefore contributions to the S parameter will be
suppressed. At the same time the experimental bounds on such Z' and W' gauge
bosons become very weak, and their masses can be lowered to make sure that
perturbative unitarity is not violated in this theory before reaching energies
of several TeV. The biggest difficulty of these models is to incorporate a
heavy top quark mass without violating any of the experimental bounds on bottom
quark gauge couplings. In the simplest models of fermion masses a sufficiently
heavy top quark also implies an unacceptably large correction to the Zb\bar{b}
vertex and a large splitting between the KK modes of the top and bottom quarks,
yielding large loop corrections to the T-parameter. We present possible
directions for model building where perhaps these constraints could be obeyed
as well.Comment: 21 pages, LaTeX, 5 figures. References and acknowledgements adde
Brane to brane gravity mediation of supersymmetry breaking
We extend the results of Mirabelli and Peskin to supergravity. We study the compactification on S-1/Z(2) of Zucker's off-shell formulation of 5D supergravity and its coupling to matter at the fixed points. We clarify some issues related to the off-shell description of supersymmetry breaking a la Scherk-Schwarz (here employed only as a tool), discussing how to deal with singular gravitino wave functions. We then consider 'visible' and 'hidden' chiral superfields localized at the two different fixed points and communicating only through 5D supergravity. We compute the one-loop corrections that mix the two sectors and the radion superfield. Locality in 5D ensures the calculability of these effects, which transmit supersymmetry breaking from the hidden to the visible sector. In the minimal set-up visible-sector scalars get a universal squared mass m(0)(2) < 0. In general (e.g., in the presence of a sizeable gravitational kinetic term localized on the hidden brane) the radion-mediated contribution to m(0)(2) can be positive and dominant. Although we did not build a complete satisfactory model, brane-to-brane effects can cure the tachyonic sleptons predicted by anomaly mediation by adding a positive m(0)(2), which is universal up to subleading flavour-breaking corrections. (C) 2003 Elsevier B.V. All rights reserved
Chiral Compactification on a Square
We study quantum field theory in six dimensions with two of them compactified
on a square. A simple boundary condition is the identification of two pairs of
adjacent sides of the square such that the values of a field at two identified
points differ by an arbitrary phase. This allows a chiral fermion content for
the four-dimensional theory obtained after integrating over the square. We find
that nontrivial solutions for the field equations exist only when the phase is
a multiple of \pi/2, so that this compactification turns out to be equivalent
to a T^2/Z_4 orbifold associated with toroidal boundary conditions that are
either periodic or anti-periodic. The equality of the Lagrangian densities at
the identified points in conjunction with six-dimensional Lorentz invariance
leads to an exact Z_8\times Z_2 symmetry, where the Z_2 parity ensures the
stability of the lightest Kaluza-Klein particle.Comment: 28 pages, latex. References added. Clarifying remarks included in
section 2. Minor corrections made in section
Electric and magnetic interaction of dyonic D-branes and odd spin structure
We present a general description of electromagnetic RR interactions between pairs of magnetically dual D-branes, focusing on the interaction of a magnetically charged brane with an electrically charged one. In the boundary state formalism, it turns out that while the electric-electric and/or magnetic-magnetic interaction corresponds to the usual RR even spin structure, the magnetic-electric interaction is described by the RR odd spin structure. As representative of the generic case of a dual pair of p and 6-p-branes, we discuss in detail the case of the self-dual 3-brane wrapped on a T-6/Z(3), which looks like an extremal dyonic black hole in four dimensions. (C) 1998 Elsevier Science B.V
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