515 research outputs found
Flux-induced SUSY-breaking soft terms on D7-D3 brane systems
We study the effect of RR and NSNS 3-form fluxes on the effective action of
the worldvolume fields of Type IIB D7/D3-brane configurations. The D7-branes
wrap 4-cycles on a local Calabi-Yau geometry. This is an extension of previous
work on hep-th/0311241, where a similar analysis was applied to the case of
D3-branes. Our present analysis is based on the D7- and D3-brane
Dirac-Born-Infeld and Chern-Simons actions, and makes full use of the
R-symmetries of the system, which allow us to compute explicitly results for
the fields lying at the D3-D7 intersections. A number of interesting new
properties appear as compared to the simpler case of configurations with only
D3-branes. As a general result one finds that fluxes stabilize some or all of
the D7-brane moduli. We argue that this is important for the problem of
stabilizing Kahler moduli through non-perturbative effects in KKLT-like vacua.
We also show that (0,3) imaginary self-dual fluxes, which lead to
compactifications with zero vacuum energy, give rise to SUSY-breaking soft
terms including gaugino and scalar masses, and trilinear terms. Particular
examples of chiral MSSM-like models of this class of vacua, based on D3-D7
brane systems at orbifold singularities are presented.Comment: 58 pages, no figures; v2: numerical factor in section 7.2 correcte
Flux Compactifications on Calabi-Yau Threefolds
The presence of RR and NS three-form fluxes in type IIB string
compactification on a Calabi-Yau orientifold gives rise to a nontrivial
superpotential W for the dilaton and complex structure moduli. This
superpotential is computable in terms of the period integrals of the Calabi-Yau
manifold. In this paper, we present explicit examples of both supersymmetric
and nonsupersymmetric solutions to the resulting 4d N=1 supersymmetric no-scale
supergravity, including some nonsupersymmetric solutions with relatively small
values of W. Our examples arise on orientifolds of the hypersurfaces in
and . They serve as explicit
illustrations of several of the ingredients which have played a role in the
recent proposals for constructing de Sitter vacua of string theory.Comment: 30 pages, harvmac big; refs and minor comments adde
Inflation and Preheating in NO models
We study inflationary models in which the effective potential of the inflaton
field does not have a minimum, but rather gradually decreases at large .
In such models the inflaton field does not oscillate after inflation, and its
effective mass becomes vanishingly small, so the standard theory of reheating
based on the decay of the oscillating inflaton field does not apply. For a long
time the only mechanism of reheating in such non-oscillatory (NO) models was
based on gravitational particle production in an expanding universe. This
mechanism is very inefficient. We will show that it may lead to cosmological
problems associated with large isocurvature fluctuations and overproduction of
dangerous relics such as gravitinos and moduli fields. We also note that the
setting of initial conditions for the stage of reheating in these models should
be reconsidered. All of these problems can be resolved in the context of the
recently proposed scenario of instant preheating if there exists an interaction
of the inflaton field with another scalar field
. We show that the mechanism of instant preheating in NO models is much
more efficient than the usual mechanism of gravitational particle production
even if the coupling constant is extremely small, .Comment: 10 pages, revte
How do violations of Gricean maxims affect reading?
Four eye-tracking experiments examined how violations of the Gricean maxim of quantity affect reading. Experiments 1 and 2 showed that first-pass reading times for size-modified definite nouns (the small towel) were longer when the modifier was redundant, as the context contained one rather than two possible referents, whereas first-pass times for bare nouns (the towel) were unaffected by whether the context contained multiple referents that resulted in ambiguity. Experiment 3 showed that unlike redundant size modifiers, redundant color modifiers did not increase first-pass times. Experiment 4 confirmed this finding, demonstrating that the effect of redundancy was dependent on the meaning of the modifier. We propose that initial referential processing is led by the lexico-semantic representation of the referring expression rather than Gricean expectations about optimal informativeness: Redundancy of a size-modifier immediately disrupts comprehension because the processor fails to activate the referential contrast implied by the meaning of the modifier, whereas referential ambiguity has no immediate effect, as it allows the activation of at least one semantically-compatible referent
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
The Lambda(b) differential production cross section and the cross section
ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum
pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7
TeV using data collected by the CMS experiment at the LHC. The measurements are
based on Lambda(b) decays reconstructed in the exclusive final state J/Psi
Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and
Lambda to proton pion, using a data sample corresponding to an integrated
luminosity of 1.9 inverse femtobarns. The product of the cross section times
the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls
faster than that of b mesons. The measured value of the cross section times the
branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06
+/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for
anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are
statistical and systematic, respectively.Comment: Submitted to Physics Letters
Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV
A search is presented for physics beyond the standard model (BSM) in final
states with a pair of opposite-sign isolated leptons accompanied by jets and
missing transverse energy. The search uses LHC data recorded at a
center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to
an integrated luminosity of approximately 5 inverse femtobarns. Two
complementary search strategies are employed. The first probes models with a
specific dilepton production mechanism that leads to a characteristic kinematic
edge in the dilepton mass distribution. The second strategy probes models of
dilepton production with heavy, colored objects that decay to final states
including invisible particles, leading to very large hadronic activity and
missing transverse energy. No evidence for an event yield in excess of the
standard model expectations is found. Upper limits on the BSM contributions to
the signal regions are deduced from the results, which are used to exclude a
region of the parameter space of the constrained minimal supersymmetric
extension of the standard model. Additional information related to detector
efficiencies and response is provided to allow testing specific models of BSM
physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO
Interface transparency of superconductor/ferromagnetic multilayers
Quantum Matter and Optic
A measurement of the neutron to 199Hg magnetic moment ratio
The neutron gyromagnetic ratio has been measured relative to that of the 199Hg atom with an uncertainty of 0.8 ppm. We employed an apparatus where ultracold neutrons and mercury atoms are stored in the same volume and report the result γn/γHg=3.8424574(30)
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