1,721,606 research outputs found
Charged and uncharged D-branes in various string theories
No full textWe describe how the D-brane spectra of the various ten-dimensional string theories can be related
to general properties of the open–closed duality, encoded in the S and P matrices of the conformal
field theory.We also complete the classification and the description of non-BPS branes in these string
theories, elucidating their non-Abelian structures and the nature of the corresponding super-Higgs
mechanisms. We find that the type 0 theories and their orientifolds have two types of uncharged
branes, distinguished by their couplings to the closed string tachyon. We also find that the 0A
orientifold has the unusual feature of having charged and uncharged branes with identical worldvolume
dimensions. We conclude with some comments on fractional branes, elucidating their role in
connection with the boundary states of Dodd SU(2)WZWmodels
Supersymmetry Breaking, Open Strings and M Theory (TOPCITE: 121 citazioni su SPIRES HEP)
No full textWe study supersymmetry breaking by Scherk-Schwarz compactifications in type I string theory.
While in the gravitational sector all mass splittings are proportional to a (large) compactification
radius, supersymmetry remains unbroken for the massless excitations of D-branes orthogonal to
the large dimension. In this sector, supersymmetry breaking can then be mediated by gravitational
interactions alone, that are expected to be suppressed by powers of the Planck mass. The mechanism
is non-perturbative from the heterotic viewpoint and requires a compactification radius
at intermediate energies of order 10~2-1014 GeV. This can also explain the value of Newton's
constant if the string scale is close to the unification scale, of order 1016 GeV
Open Descendants of Freely Acting Z2 x Z2 Orientifolds (TOPCITE: 65 citazioni su SPIRES HEP)
No full textWe discuss Z2=Z2 orientifolds where the orbifold twists are accompanied by shifts on
momentum or winding lattice states. The models contain variable numbers of D5-branes, whose
massless and, at times, even massive. modes have variable numbers of supersymmetries. We
display new type-I models with partial supersymmetry breaking Ns2TMNs1, Ns4TMNs1
and Ns4TMNs2. The geometry of these models is rather rich: the shift operations create brane
multiplets related by orbifold transformations that support gauge groups of reduced rank. Some of
the models are deformations of six-dimensional supersymmetric type-I models, while others have
dual M-theory descriptions
Partial Breaking of Supersymmetry, Open Strings and M Theory (TOPCITE: 103 citazioni su SPIRES HEP)
No full textWe study total and partial supersymmetry breakingQ0y freely acting orbifolds, or equivalently
by Scherk-Schwarz compactifications, in type I strifig theory. In particular, we describe a fourdimensional
chirat compactification with spontaneously broken N = 1 supersymmetry, some models
with partial N = 4 ---+ N = 2 and N = 4 ---+ N = 1 supersymmetry breaking and their heterotic
and M-theory duals. A generic feature of these models is that in the gravitational sector and in the
spectrum of D-branes parallel to the breaking coordinate, all mass splittings are proportional to
the compactification scale, while global (extended) supersymmetry remains unbroken at tree level
for the massless excitations of D-branes transverse to the breaking direction
Type-I Strings on Magnetised Orbifolds and Brane Transmutation (TOPCITE: 256 citazioni su INSPIRE HEP)
No full textIn the presence of internal magnetic fields, a D9 brane can acquire a D5 (or anti-D5) R-R charge, and can therefore contribute to the corresponding tadpole. In the resulting vacua, supersymmetry is generically broken and tachyonic instabilities are present. However, suitable choices for the magnetic fields, corresponding to self-dual configurations in the internal space, can yield new chiral supersymmetric vacua with gauge groups of reduced rank, where the magnetic energy saturates, partly or fully, the negative tension of the O5+ planes. These models contain Green-Schwarz couplings to untwisted R-R forms not present in conventional orientifolds
Brane supersymmetry breaking
No full textWe show how to construct chiral tachyon-free perturbative orientifold models, where supersymmetry is broken at the
string scale on a collection of branes while, to lowest order, the bulk and the other branes are supersymmetric. In higher
orders, supersymmetry breaking is mediated to the remaining sectors, but is suppressed by the size of the transverse space or
by the distance from the brane where supersymmetry breaking primarily occurred. This setting is of interest for orbifold
models with discrete torsion, and is of direct relevance for low-scale string models. It can guarantee the stability of the gauge
hierarchy against gravitational radiative corrections, allowing an almost exact supergravity a millimeter away from a
non-supersymmetric world
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