914 research outputs found
Behavior sensitivities for control augmented structures
During the past few years it has been recognized that combining passive structural design methods with active control techniques offers the prospect of being able to find substantially improved designs. These developments have stimulated interest in augmenting structural synthesis by adding active control system design variables to those usually considered in structural optimization. An essential step in extending the approximation concepts approach to control augmented structural synthesis is the development of a behavior sensitivity analysis capability for determining rates of change of dynamic response quantities with respect to changes in structural and control system design variables. Behavior sensitivity information is also useful for man-machine interactive design as well as in the context of system identification studies. Behavior sensitivity formulations for both steady state and transient response are presented and the quality of the resulting derivative information is evaluated
Black Hole Formation and Classicalization in Ultra-Planckian 2 -> N Scattering
We establish a connection between the ultra-Planckian scattering amplitudes
in field and string theory and unitarization by black hole formation in these
scattering processes. Using as a guideline an explicit microscopic theory in
which the black hole represents a bound-state of many soft gravitons at the
quantum critical point, we were able to identify and compute a set of
perturbative amplitudes relevant for black hole formation. These are the
tree-level N-graviton scattering S-matrix elements in a kinematical regime
(called classicalization limit) where the two incoming ultra-Planckian
gravitons produce a large number N of soft gravitons. We compute these
amplitudes by using the Kawai-Lewellen-Tye relations, as well as scattering
equations and string theory techniques. We discover that this limit reveals the
key features of the microscopic corpuscular black hole N-portrait. In
particular, the perturbative suppression factor of a N-graviton final state,
derived from the amplitude, matches the non-perturbative black hole entropy
when N reaches the quantum criticality value, whereas final states with
different value of N are either suppressed or excluded by non-perturbative
corpuscular physics. Thus we identify the microscopic reason behind the black
hole dominance over other final states including non-black hole classical
object. In the parameterization of the classicalization limit the scattering
equations can be solved exactly allowing us to obtain closed expressions for
the high-energy limit of the open and closed superstring tree-level scattering
amplitudes for a generic number N of external legs. We demonstrate matching and
complementarity between the string theory and field theory in different large-s
and large-N regimes.Comment: 55 pages, 7 figures, LaTeX; v2: typos removed; final version to
appear in Nucl. Phys.
Minimal left-right symmetric intersecting D-brane model
We investigate left-right symmetric extensions of the standard model based on
open strings ending on D-branes, with gauge bosons due to strings attached to
stacks of D-branes and chiral matter due to strings stretching between
intersecting D-branes. The left-handed and right-handed fermions transform as
doublets under Sp(1)_L and Sp(1)_R, and so their masses must be generated by
the introduction of Higgs fields in a bi-fundamental (2,2) representation under
the two Sp(1) gauge groups. For such D-brane configurations the left-right
symmetry must be broken by Higgs fields in the doublet representation of
Sp(1)_R and therefore Majorana mass terms are suppressed by some higher physics
scale. The left-handed and right-handed neutrinos pair up to form Dirac
fermions which control the decay widths of the right-handed W' boson to yield
comparable branching fractions into dilepton and dijets channels. Using the
most recent searches at LHC13 Run II with 2016 data we constrain the (g_R,
m_{W'}) parameter space. Our analysis indicates that independent of the
coupling strength g_R, gauge bosons with masses m_{W'} \agt 3.5~{\rm TeV} are
not ruled out. As the LHC is just beginning to probe the TeV-scale, significant
room for W' discovery remains.Comment: To be published in PR
Production Profitability of Ethanol from Alternative Feedstocks in the Texas Panhandle
The potential of three feedstocks: grain sorghum, sweet sorghum, and switchgrass for ethanol production in the top 26 counties of the Texas Panhandle Region is analyzed using yield and production costs of feedstock, processing cost of feedstock, final demand for ethanol, farm to wholesale marketing margin, and the derived demand price of feedstock. The calculated economic returns per acre of grain sorghum, sweet sorghum, and switchgrass are -410.19, and -38.25, -29.04 respectively under dryland condition. The evaluation in this study demonstrates that ethanol production from grain sorghum, sweet sorghum, and switchgrass in the Texas Panhandle Region is not economically feasible given the current price for ethanol in Texas. This is consistent with the status of the ethanol industry in the Texas Panhandle.Ethanol production, Texas Panhandle, Grain sorghum, Sweet sorghum, and Switchgrass, Feedstock, Crop Production/Industries, Production Economics, Resource /Energy Economics and Policy, Q16, Q25, Q27, and Q42,
Update on 750 GeV diphotons from closed string states
Motivated by the recent update on LHC searches for narrow and broad
resonances decaying into diphotons we reconsider the possibility that the
observed peak in the invariant mass spectrum at M_{\gamma \gamma} = 750 GeV
originates from a closed string (possibly axionic) excitation \varphi
(associated with low mass scale string theory) that has a coupling with gauge
kinetic terms. We reevaluate the production of \varphi by photon fusion to
accommodate recent developments on additional contributions to relativistic
light-light scattering. We also study the production of \varphi via gluon
fusion. We show that for both a narrow and a broad resonance these two initial
topologies can accommodate the excess of events, spanning a wide range of
string mass scales 7 \alt M_s/TeV \alt 30 that are consistent with the
experimental lower bound: M_s > 7 TeV, at 95% CL. We demonstrate that for the
two production processes the LHC13 data is compatible with the lack of a
diphoton excess in LHC8 data within \sim 1\sigma. We also show that if the
resonance production is dominated by gluon fusion the null results on dijet
searches at LHC8 further constrain the coupling strengths of \varphi, but
without altering the range of possible string mass scales.Comment: 11 pages revtex. arXiv admin note: text overlap with arXiv:1512.0850
Stringy origin of diboson and dijet excesses at the LHC
Very recently, the ATLAS and CMS collaborations reported diboson and dijet
excesses above standard model expectations in the invariant mass region of 1.8
-2.0 TeV. Interpreting the diboson excess of events in a model independent
fashion suggests that the vector boson pair production searches are best
described by WZ or ZZ topologies, because states decaying into W^+W^- pairs are
strongly constrained by semileptonic searches. Under the assumption of a low
string scale, we show that both the diboson and dijet excesses can be steered
by an anomalous U(1) field with very small coupling to leptons. The Drell-Yan
bounds are then readily avoided because of the leptophobic nature of the
massive Z' gauge boson. The non-negligible decay into ZZ required to
accommodate the data is a characteristic footprint of intersecting D-brane
models, wherein the Landau-Yang theorem can be evaded by anomaly-induced
operators involving a longitudinal Z. The model presented herein can be viewed
purely field-theoretically, although it is particularly well motivated from
string theory. Should the excesses become statistically significant at the
LHC13, the associated Z\gamma{} topology would become a signature consistent
only with a stringy origin.Comment: References added. To be published in PL
Vacuum Stability of Standard Model^{++}
The latest results of the ATLAS and CMS experiments point to a preferred
narrow Higgs mass range (m_h \simeq 124 - 126 GeV) in which the effective
potential of the Standard Model (SM) develops a vacuum instability at a scale
10^{9} -10^{11} GeV, with the precise scale depending on the precise value of
the top quark mass and the strong coupling constant. Motivated by this
experimental situation, we present here a detailed investigation about the
stability of the SM^{++} vacuum, which is characterized by a simple extension
of the SM obtained by adding to the scalar sector a complex SU(2) singlet that
has the quantum numbers of the right-handed neutrino, H", and to the gauge
sector an U(1) that is broken by the vacuum expectation value of H". We derive
the complete set of renormalization group equations at one loop. We then pursue
a numerical study of the system to determine the triviality and vacuum
stability bounds, using a scan of 10^4 random set of points to fix the initial
conditions. We show that, if there is no mixing in the scalar sector, the top
Yukawa coupling drives the quartic Higgs coupling to negative values in the
ultraviolet and, as for the SM, the effective potential develops an instability
below the Planck scale. However, for a mixing angle -0.35 \alt \alpha \alt
-0.02 or 0.01 \alt \alpha \alt 0.35, with the new scalar mass in the range 500
GeV \alt m_{h"} \alt 8 TeV, the SM^{++} ground state can be absolutely stable
up to the Planck scale. These results are largely independent of TeV-scale free
parameters in the model: the mass of the non-anomalous U(1) gauge boson and its
branching fractions.Comment: 17 revtex pages, 8 figures; to be published in JHE
NUT-Charged Black Holes in Gauss-Bonnet Gravity
We investigate the existence of Taub-NUT/bolt solutions in Gauss-Bonnet
gravity and obtain the general form of these solutions in dimensions. We
find that for all non-extremal NUT solutions of Einstein gravity having no
curvature singularity at , there exist NUT solutions in Gauss-Bonnet
gravity that contain these solutions in the limit that the Gauss-Bonnet
parameter goes to zero. Furthermore there are no NUT solutions in
Gauss-Bonnet gravity that yield non-extremal NUT solutions to Einstein gravity
having a curvature singularity at in the limit . Indeed,
we have non-extreme NUT solutions in dimensions with non-trivial
fibration only when the -dimensional base space is chosen to be
. We also find that the Gauss-Bonnet gravity has extremal NUT
solutions whenever the base space is a product of 2-torii with at most a
2-dimensional factor space of positive curvature. Indeed, when the base space
has at most one positively curved two dimensional space as one of its factor
spaces, then Gauss-Bonnet gravity admits extreme NUT solutions, even though
there a curvature singularity exists at . We also find that one can have
bolt solutions in Gauss-Bonnet gravity with any base space with factor spaces
of zero or positive constant curvature. The only case for which one does not
have bolt solutions is in the absence of a cosmological term with zero
curvature base space.Comment: 20 pages, referrence added, a few typos correcte
Brane world effective actions for D-branes with fluxes
We develop systematic string techniques to study brane world effective
actions for models with magnetized (or equivalently intersecting) D-branes. In
particular, we derive the dependence on all NS-NS moduli of the kinetic terms
of the chiral matter in a generic non-supersymmetric brane configurations with
non-commuting open string fluxes. Near a N=1 supersymmetric point the effective
action is consistent with a Fayet-Iliopoulos supersymmetry breaking and the
normalization of the scalar kinetic terms is nothing else than the Kahler
metric. We also discuss, from a stringy perspective, D and F term breaking
mechanisms, and how, in this generic set up, the Kahler metric enters in the
physical Yukawa couplings.Comment: 52 pages, 3 figures; several references adde
- âŠ