96 research outputs found
Penrose Limits, Deformed pp-Waves and the String Duals of N=1 Large n Gauge Theory
A certain conformally invariant N=1 supersymmetric SU(n) gauge theory has a
description as an infra-red fixed point obtained by deforming the N=4
supersymmetric Yang-Mills theory by giving a mass to one of its N=1 chiral
multiplets. We study the Penrose limit of the supergravity dual of the large n
limit of this N=1 gauge theory. The limit gives a pp-wave with R-R five-form
flux and both R-R and NS-NS three-form flux. We discover that this new solution
preserves twenty supercharges and that, in the light-cone gauge, string theory
on this background is exactly solvable. Correspondingly, this latter is the
stringy dual of a particular large charge limit of the large n gauge theory. We
are able to identify which operators in the field theory survive the limit to
form the string's ground state and some of the spacetime excitations. The full
string model, which we exhibit, contains a family of non-trivial predictions
for the properties of the gauge theory operators which survive the limit.Comment: 39 pages, Late
Semiclassical quantization of Rotating Strings in Pilch-Warner geometry
Some of the recent important developments in understanding string/ gauge
dualities are based on the idea of highly symmetric motion of ``string
solitons'' in geometry originally suggested by Gubser,
Klebanov and Polyakov. In this paper we study symmetric motion of certain
string configurations in so called Pilch-Warner geometry. The two-form field
breaks down the supersymmetry to but for the string
configurations considered in this paper the classical values of the energy and
the spin are the same as for string in . Although trivial at
classical level, the presence of NS-NS antisymmetric field couples the
fluctuation modes that indicates changes in the quantum corrections to the
energy spectrum. We compare our results with those obtained in the case of
pp-wave limit in hep-th/0206045.Comment: 31 pages, no figures, v2 - a few typos correcte
Compilation of extended recursion in call-by-value functional languages
This paper formalizes and proves correct a compilation scheme for
mutually-recursive definitions in call-by-value functional languages. This
scheme supports a wider range of recursive definitions than previous methods.
We formalize our technique as a translation scheme to a lambda-calculus
featuring in-place update of memory blocks, and prove the translation to be
correct.Comment: 62 pages, uses pi
Killing spectroscopy of closed timelike curves
We analyse the existence of closed timelike curves in spacetimes which
possess an isometry. In particular we check which discrete quotients of such
spaces lead to closed timelike curves. As a by-product of our analysis, we
prove that the notion of existence or non-existence of closed timelike curves
is a T-duality invariant notion, whenever the direction along which we apply
such transformations is everywhere spacelike. Our formalism is
straightforwardly applied to supersymmetric theories. We provide some new
examples in the context of D-branes and generalized pp-waves.Comment: 1+35 pages, no figures; v2, new references added. Final version to
appear in JHE
Non-BPS D-Branes in Light-Cone Green-Schwarz Formalism
Non-BPS D-branes are difficult to describe covariantly in a manifestly
supersymmetric formalism. For definiteness we concentrate on type IIB string
theory in flat background in light-cone Green-Schwarz formalism. We study both
the boundary state and the boundary conformal field theory descriptions of
these D-branes with manifest SO(8) covariance and go through various
consistency checks. We analyze Sen's original construction of non-BPS D-branes
given in terms of an orbifold boundary conformal field theory. We also directly
study the relevant world-sheet theory by deriving the open string boundary
condition from the covariant boundary state. Both these methods give the same
open string spectrum which is consistent with the boundary state, as required
by the world-sheet duality. The boundary condition found in the second method
is given in terms of bi-local fields that are quadratic in Green-Schwarz
fermions. We design a special ``doubling trick'' suitable to handle such
boundary conditions and prescribe rules for computing all possible correlation
functions without boundary insertions. This prescription has been tested by
computing disk one-point functions of several classes of closed string states
and comparing the results with the boundary state computation.Comment: 47 pages, 1 figure. Typos corrected, references added and slight
modification of certain explanation made. Version accepted for publication in
JHE
M-theory lift of brane-antibrane systems and localised closed string tachyons
We discuss the lift of certain D6-antiD6-brane systems to M-theory. These are
purely gravitational configurations with a bolt singularity. When reduced along
a trivial circle, and for large bolt radius, the bolt is related to a
non-supersymmetric orbifold type of singularity where some closed string
tachyons are expected in the twisted sectors. This is a kind of open-closed
string duality that relates open string tachyons on one side and localised
tachyons in the other. We consider the evolution of the system of branes from
M-theory point of view. This evolution gives rise to a brane-antibrane
annihilation on the brane side. On the gravity side, the evolution is related
to a reduction of the order of the orbifold and to a contraction of the bolt to
a nut or flat space if the system has non-vanishing or vanishing charge,
respectively. We also consider the inverse process of reducing a
non-supersymmetric orbifold to a D6-brane system. For , the
reduced system is a fractional D6-brane at an orbifold singularity .Comment: 1+22 pages, 5 figures; v2 comments on the M-theory geometry and
further references adde
The interspecific growth–mortality trade-off is not a general framework for tropical forest community structure
Resource allocation within trees is a zero-sum game. Unavoidable trade-offs dictate that allocation to growth-promoting functions curtails other functions, generating a gradient of investment in growth versus survival along which tree species align, known as the interspecific growth–mortality trade-off. This paradigm is widely accepted but not well established. Using demographic data for 1,111 tree species across ten tropical forests, we tested the generality of the growth–mortality trade-off and evaluated its underlying drivers using two species-specific parameters describing resource allocation strategies: tolerance of resource limitation and responsiveness of allocation to resource access. Globally, a canonical growth–mortality trade-off emerged, but the trade-off was strongly observed only in less disturbance-prone forests, which contained diverse resource allocation strategies. Only half of disturbance-prone forests, which lacked tolerant species, exhibited the trade-off. Supported by a theoretical model, our findings raise questions about whether the growth–mortality trade-off is a universally applicable organizing framework for understanding tropical forest community structure
Prevalence of Frailty in European Emergency Departments (FEED): an international flash mob study
Introduction
Current emergency care systems are not optimized to respond to multiple and complex problems associated with frailty. Services may require reconfiguration to effectively deliver comprehensive frailty care, yet its prevalence and variation are poorly understood. This study primarily determined the prevalence of frailty among older people attending emergency care.
Methods
This cross-sectional study used a flash mob approach to collect observational European emergency care data over a 24-h period (04 July 2023). Sites were identified through the European Task Force for Geriatric Emergency Medicine collaboration and social media. Data were collected for all individuals aged 65 + who attended emergency care, and for all adults aged 18 + at a subset of sites. Variables included demographics, Clinical Frailty Scale (CFS), vital signs, and disposition. European and national frailty prevalence was determined with proportions with each CFS level and with dichotomized CFS 5 + (mild or more severe frailty).
Results
Sixty-two sites in fourteen European countries recruited five thousand seven hundred eighty-five individuals. 40% of 3479 older people had at least mild frailty, with countries ranging from 26 to 51%. They had median age 77 (IQR, 13) years and 53% were female. Across 22 sites observing all adult attenders, older people living with frailty comprised 14%.
Conclusion
40% of older people using European emergency care had CFS 5 + . Frailty prevalence varied widely among European care systems. These differences likely reflected entrance selection and provide windows of opportunity for system configuration and workforce planning
First measurement of Ωc0 production in pp collisions at s=13 TeV
The inclusive production of the charm–strange baryon 0 c is measured for the first time via its hadronic √ decay into −π+ at midrapidity (|y| <0.5) in proton–proton (pp) collisions at the centre-of-mass energy s =13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 < pT < 12 GeV/c. The pT dependence of the 0 c-baryon production relative to the prompt D0-meson and to the prompt 0 c-baryon production is compared to various models that take different hadronisation mechanisms into consideration. In the measured pT interval, the ratio of the pT-integrated cross sections of 0 c and prompt + c baryons multiplied by the −π+ branching ratio is found to be larger by a factor of about 20 with a significance of about 4σ when compared to e+e− collisions
Elliptic flow of charged particles at midrapidity relative to the spectator plane in Pb–Pb and Xe–Xe collisions
Measurements of the elliptic flow coefficient relative to the collision plane defined by the spectator neutrons v2{ SP} in collisions of Pb ions at center-of-mass energy per nucleon–nucleon pair √ 2.76 TeV and Xe ions at √ sNN = sNN =5.44 TeV are reported. The results are presented for charged particles produced at midrapidity as a function of centrality and transverse momentum for the 5–70% and 0.2–6 GeV/c ranges, respectively. The ratio between v2{ SP} and the elliptic flow coefficient relative to the participant plane v2{4}, estimated using four-particle correlations, deviates by up to 20% from unity depending on centrality. This observation differs strongly from the magnitude of the corresponding eccentricity ratios predicted by the TRENTo and the elliptic power models of initial state fluctuations that are tuned to describe the participant plane anisotropies. The differences can be interpreted as a decorrelation of the neutron spectator plane and the reaction plane because of fragmentation of the remnants from the colliding nuclei, which points to an incompleteness of current models describing the initial state fluctuations. A significant transverse momentum dependence of the ratio v2{ SP}/v2{4} is observed in all but the most central collisions, which may help to understand whether momentum anisotropies at low and intermediate transverse momentum have a common origin in initial state f luctuations. The ratios of v2{ SP} and v2{4} to the corresponding initial state eccentricities for Xe–Xe and Pb–Pb collisions at similar initial entropy density show a difference of (7.0 ±0.9)%with an additional variation of +1.8% when including RHIC data in the TRENTo parameter extraction. These observations provide new experimental constraints for viscous effects in the hydrodynamic modeling of the expanding quark–gluon plasma produced in heavy-ion collisions at the LHC
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