491 research outputs found
Higher derivative terms including the Ramond-Ramond five-form
Superfield methods can be used to determine the precise way the self-dual
five-form couples to the metric in the first non-trivial corrections
to type IIB supergravity. We explicitly compute the exact tensor structure of
these terms. This requires extensive use of computing algorithms to reduce the
complicated expressions that appear to a surprisingly simple form. Along the
way we show a new method of computing Schouten identities. With this result we
clarify under which conditions one may neglect the five-form higher derivative
terms. We comment on corrections to the thermodynamics of charged black holes.Comment: v2 - Numerical typos fixed, small text changes
Risk-based Spacecraft Fire Safety Experiments
Viewgraphs on risk-based spacecraft fire safety experiments are presented. Spacecraft fire risk can never be reduced to a zero probability. Probabilistic risk assessment is a tool to reduce risk to an acceptable level
Solving the 3D Ising Model with the Conformal Bootstrap
We study the constraints of crossing symmetry and unitarity in general 3D
Conformal Field Theories. In doing so we derive new results for conformal
blocks appearing in four-point functions of scalars and present an efficient
method for their computation in arbitrary space-time dimension. Comparing the
resulting bounds on operator dimensions and OPE coefficients in 3D to known
results, we find that the 3D Ising model lies at a corner point on the boundary
of the allowed parameter space. We also derive general upper bounds on the
dimensions of higher spin operators, relevant in the context of theories with
weakly broken higher spin symmetries.Comment: 32 pages, 11 figures; v2: refs added, small changes in Section 5.3,
Fig. 7 replaced; v3: ref added, fits redone in Section 5.
Entropy Bound and Causality Violation in Higher Curvature Gravity
In any quantum theory of gravity we do expect corrections to Einstein gravity
to occur. Yet, at fundamental level, it is not apparent what the most relevant
corrections are. We argue that the generic curvature square corrections present
in lower dimensional actions of various compactified string theories provide a
natural passage between the classical and quantum realms of gravity. The
Gauss-Bonnet and gravities, in particular, provide concrete
examples in which inconsistency of a theory, such as, a violation of
microcausality, and a classical limit on black hole entropy are correlated. In
such theories the ratio of the shear viscosity to the entropy density,
, can be smaller than for a boundary conformal field theory with
Einstein gravity dual. This result is interesting from the viewpoint that the
nuclear matter or quark-gluon plasma produced (such as at RHIC) under extreme
densities and temperatures may violate the conjectured bound , {\it albeit} marginally so.Comment: 23 pages, several eps figures; minor changes, references added,
published versio
Massive Gravity Theories and limits of Ghost-free Bigravity models
We construct a class of theories which extend New Massive Gravity to higher
orders in curvature in any dimension. The lagrangians arise as limits of a new
class of bimetric theories of Lovelock gravity, which are unitary theories free
from the Boulware-Deser ghost. These Lovelock bigravity models represent the
most general non-chiral ghost-free theories of an interacting massless and
massive spin-two field in any dimension. The scaling limit is taken in such a
way that unitarity is explicitly broken, but the Boulware-Deser ghost remains
absent. This automatically implies the existence of a holographic -theorem
for these theories. We also show that the Born-Infeld extension of New Massive
Gravity falls into our class of models demonstrating that this theory is also
free of the Boulware-Deser ghost. These results extend existing connections
between New Massive Gravity, bigravity theories, Galileon theories and
holographic -theorems.Comment: 11+5 page
A note on the quartic effective action of type IIB superstring
We recast the result of our recent computation of the quartic action of
ten-dimensional IIB supergravity in a manifestly SL(2,R)-covariant form. This
affords us a critical assessment of an earlier conjecture in the literature.Comment: 15 pages; v2: some clarifications and a rerence adde
AdS_7/CFT_6, Gauss-Bonnet Gravity, and Viscosity Bound
We study the relation between the causality and the positivity of energy
bounds in Gauss-Bonnet gravity in AdS_7 background and find a precise
agreement. Requiring the group velocity of metastable states to be bounded by
the speed of light places a bound on the value of Gauss-Bonnet coupling. To
find the positivity of energy constraints we compute the parameters which
determine the angular distribution of the energy flux in terms of three
independent coefficients specifying the three-point function of the
stress-energy tensor. We then relate the latter to the Weyl anomaly of the
six-dimensional CFT and compute the anomaly holographically. The resulting
upper bound on the Gauss-Bonnet coupling coincides with that from causality and
results in a new bound on viscosity/entropy ratio.Comment: 21 page, harvmac; v2: reference adde
Lessons from crossing symmetry at large N
20 pages, v2: Assumptions stated more clearly, version published in JHEPWe consider the four-point correlator of the stress tensor multiplet in N=4 SYM. We construct all solutions consistent with crossing symmetry in the limit of large central charge c ~ N^2 and large g^2 N. While we find an infinite tower of solutions, we argue most of them are suppressed by an extra scale \Delta_{gap} and are consistent with the upper bounds for the scaling dimension of unprotected operators observed in the numerical superconformal bootstrap at large central charge. These solutions organize as a double expansion in 1/c and 1/\Delta_{gap}. Our solutions are valid to leading order in 1/c and to all orders in 1/\Delta_{gap} and reproduce, in particular, instanton corrections previously found. Furthermore, we find a connection between such upper bounds and positivity constraints arising from causality in flat space. Finally, we show that certain relations derived from causality constraints for scattering in AdS follow from crossing symmetry.Peer reviewe
Potential clinical implications of CD4+CD26high T cells for nivolumab treated melanoma patients
Background Nivolumab is an anti-PD1 antibody that has dramatically improved metastatic melanoma patientsâ
outcomes. Nevertheless, many patients are resistant to PD-1 inhibition, occasionally experiencing severe of-target
immune toxicity. In addition, no robust and reproducible biomarkers have yet been validated to identify the correct selection of patients who will beneft from anti-PD-1 treatment avoiding unwanted side efects. However, the
strength of CD26 expression on CD4+ T lymphocytes permits the characterization of three subtypes with variable
degrees of responsiveness to tumors, suggesting that the presence of CD26-expressing T cells in patients might be a
marker of responsiveness to PD-1-based therapies.
Methods The frequency distribution of peripheral blood CD26-expressing cells was investigated employing multiparametric fow cytometry in 69 metastatic melanoma patients along with clinical characteristics and blood count
parameters at baseline (W0) and compared to 20 age- and sex-matched healthy controls. Percentages of baseline
CD4+CD26high T cells were correlated with the outcome after nivolumab treatment. In addition, the frequency of
CD4+CD26high T cells at W0 was compared with those obtained after 12 weeks (W1) of therapy in a sub-cohort of 33
patients.
Results Circulating CD4+CD26high T cells were signifcantly reduced in melanoma patients compared to healthy
subjects (p=0.001). In addition, a signifcant association was observed between a low baseline percentage of
CD4+CD26high T cells (<7.3%) and clinical outcomes, measured as overall survival (p=0.010) and progression-free
survival (p=0.014). Moreover, patients with clinical beneft from nivolumab therapy had signifcantly higher frequencies of circulating CD4+CD26high T cells than patients with non-clinical beneft (p=0.004) at 12 months. Also, a higher
pre-treatment proportion of circulating CD4+CD26high T cells was correlated with Disease Control Rate (p=0.014)
and best Overall Response Rate (p=0.009) at 12 months. Interestingly, after 12 weeks (W1) of nivolumab treatment,
percentages of CD4+CD26high T cells were signifcantly higher in comparison with the frequencies measured at W0
(p<0.0001), aligning the cell counts with the ranges seen in the blood of healthy subjects
Holographic studies of quasi-topological gravity
Quasi-topological gravity is a new gravitational theory including
curvature-cubed interactions and for which exact black hole solutions were
constructed. In a holographic framework, classical quasi-topological gravity
can be thought to be dual to the large limit of some non-supersymmetric
but conformal gauge theory. We establish various elements of the AdS/CFT
dictionary for this duality. This allows us to infer physical constraints on
the couplings in the gravitational theory. Further we use holography to
investigate hydrodynamic aspects of the dual gauge theory. In particular, we
find that the minimum value of the shear-viscosity-to-entropy-density ratio for
this model is .Comment: 45 pages, 6 figures. v2: References adde
- âŠ