1,721,146 research outputs found
Mass Scales, Supersymmetry Breaking and Open Strings
No full textWe review physical motivations and possible realizations of string vacua with large internal volume and/or low string scale and discuss the issue of supersymmetry breaking. In particular, we describe the key features of Scherk-Schwarz deformations in type I models and conclude by reviewing the phenomenon of ``brane supersymmetry breaking'': the tadpole conditions of some type-I models require that supersymmetry be {\it broken at the string scale} on a collection of branes, while being exact, to lowest order, in the bulk and on other branes
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
Gauged Supergravity Vacua in String Theory (TOPCITE: 63 citazioni su SPIRES HEP)
No full textWe present a first instance of an exact supersymmetric string vacuum in curved space-time. It corresponds to the Freedman-
Gibbons electrovac solution to one version of N= 4 supergravity, with N= 2 space-time supersymmetry. The conformal theory
includes a Wess-Zumino-Witten model on the SU ( 1, 1 ) group manifold
Partial breaking of supersymmetry, open strings and M-theory
Get PDFWe study total and partial supersymmetry breaking by freely acting orbifolds, or equivalently by Scherk-Schwarz compactifications, in type I string theory. In particular, we describe a four-dimensional chiral compactification with spontaneously broken N=1 supersymmetry, some models with partial and 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.We study total and partial supersymmetry breaking by freely acting orbifolds, or equivalently by Scherk-Schwarz compactifications, in type I string theory. In particular, we describe a four-dimensional chiral compactification with spontaneously broken N=1 supersymmetry, some models with partial and 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.We study total and partial supersymmetry breaking by freely acting orbifolds, or equivalently by Scherk-Schwarz compactifications, in type I string theory. In particular, we describe a four-dimensional chiral compactification with spontaneously broken N=1 supersymmetry, some models with partial and 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.We study total and partial supersymmetry breaking by freely acting orbifolds, or equivalently by Scherk-Schwarz compactifications, in type I string theory. In particular, we describe a four-dimensional chiral 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
Phenomenology of a leptonic goldstino and invisible Higgs boson decays
No full textNon-linearly realized supersymmetry, combined with the Standard Model field content and SU(3)XSU(2)XU(1) gauge invariance, permits local dimension-six operators involving a goldstino, a lepton doublet and a Higgs doublet. These interactions preserve total lepton number if the left-handed goldstino transforms as an antilepton. We discuss the resulting phenomenology, in the simple limit where the new couplings involve only one lepton family, thus conserving also lepton flavour. Both the Z boson and the Higgs boson can decay into a neutrino and a goldstino: the present limits from the invisible Z width and from other observables leave room for the striking possibility of a Higgs boson decaying dominantly, or at least with a sizable branching ratio, via such an invisible mode. We finally comment on the perspectives at hadron and lepton colliders, and on possible extensions of our analysis.Non-linearly realized supersymmetry, combined with the Standard Model field content and SU(3)XSU(2)XU(1) gauge invariance, permits local dimension-six operators involving a goldstino, a lepton doublet and a Higgs doublet. These interactions preserve total lepton number if the left-handed goldstino transforms as an antilepton. We discuss the resulting phenomenology, in the simple limit where the new couplings involve only one lepton family, thus conserving also lepton flavour. Both the Z boson and the Higgs boson can decay into a neutrino and a goldstino: the present limits from the invisible Z width and from other observables leave room for the striking possibility of a Higgs boson decaying dominantly, or at least with a sizable branching ratio, via such an invisible mode. We finally comment on the perspectives at hadron and lepton colliders, and on possible extensions of our analysis.Non-linearly realized supersymmetry, combined with the Standard Model field content and SU ( 3 ) × SU ( 2 ) × U ( 1 ) gauge invariance, permits local dimension-six operators involving a goldstino, a lepton doublet and a Higgs doublet. These interactions preserve total lepton number if the left-handed goldstino transforms as an antilepton. We discuss the resulting phenomenology, in the simple limit where the new couplings involve only one lepton family, thus conserving also lepton flavour. Both the Z boson and the Higgs boson can decay into a neutrino and a goldstino: the present limits from the invisible Z width and from other observables leave room for the striking possibility of a Higgs boson decaying dominantly, or at least with a sizable branching ratio, via such an invisible mode. We finally comment on the perspectives at hadron and lepton colliders, and on possible extensions of our analysis
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
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
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
- …
