257 research outputs found
Graviton Vertices and the Mapping of Anomalous Correlators to Momentum Space for a General Conformal Field Theory
We investigate the mapping of conformal correlators and of their anomalies
from configuration to momentum space for general dimensions, focusing on the
anomalous correlators , - involving the energy-momentum tensor
with a vector or a scalar operator () - and the 3-graviton vertex
. We compute the , and one-loop vertex functions in
dimensional regularization for free field theories involving conformal scalar,
fermion and vector fields. Since there are only one or two independent tensor
structures solving all the conformal Ward identities for the or
vertex functions respectively, and three independent tensor structures for the
vertex, and the coefficients of these tensors are known for free fields,
it is possible to identify the corresponding tensors in momentum space from the
computation of the correlators for free fields. This works in general
dimensions for and correlators, but only in 4 dimensions for ,
since vector fields are conformal only in . In this way the general
solution of the Ward identities including anomalous ones for these correlators
in (Euclidean) position space, found by Osborn and Petkou is mapped to the
ordinary diagrammatic one in momentum space. We give simplified expressions of
all these correlators in configuration space which are explicitly Fourier
integrable and provide a diagrammatic interpretation of all the contact terms
arising when two or more of the points coincide. We discuss how the anomalies
arise in each approach [...]Comment: 57 pages, 7 figures. Refs adde
The -theorem and the Asymptotics of 4D Quantum Field Theory
We study the possible IR and UV asymptotics of 4D Lorentz invariant unitary
quantum field theory. Our main tool is a generalization of the
Komargodski-Schwimmer proof for the -theorem. We use this to rule out a
large class of renormalization group flows that do not asymptote to conformal
field theories in the UV and IR. We show that if the IR (UV) asymptotics is
described by perturbation theory, all beta functions must vanish faster than
as (). This implies that the
only possible asymptotics within perturbation theory is conformal field theory.
In particular, it rules out perturbative theories with scale but not conformal
invariance, which are equivalent to theories with renormalization group
pseudocycles. Our arguments hold even for theories with gravitational
anomalies. We also give a non-perturbative argument that excludes theories with
scale but not conformal invariance. This argument holds for theories in which
the stress-energy tensor is sufficiently nontrivial in a technical sense that
we make precise.Comment: 41 pages, 2 figures. v2: Arguments clarified, some side comments
corrected, connection to previous work by Jack and Osborn described,
conclusions unaffecte
Duality Invariant Actions and Generalised Geometry
We construct the non-linear realisation of the semi-direct product of E(11)
and its first fundamental representation at lowest order and appropriate to
spacetime dimensions four to seven. This leads to a non-linear realisation of
the duality groups and introduces fields that depend on a generalised space
which possess a generalised vielbein. We focus on the part of the generalised
space on which the duality groups alone act and construct an invariant action.Comment: 59 pages (typos fixed and added comments
Lorentz violation, Gravity, Dissipation and Holography
We reconsider Lorentz Violation (LV) at the fundamental level. We show that
Lorentz Violation is intimately connected with gravity and that LV couplings in
QFT must always be fields in a gravitational sector. Diffeomorphism invariance
must be intact and the LV couplings transform as tensors under coordinate/frame
changes. Therefore searching for LV is one of the most sensitive ways of
looking for new physics, either new interactions or modifications of known
ones. Energy dissipation/Cerenkov radiation is shown to be a generic feature of
LV in QFT. A general computation is done in strongly coupled theories with
gravity duals. It is shown that in scale invariant regimes, the energy
dissipation rate depends non-triviallly on two characteristic exponents, the
Lifshitz exponent and the hyperscaling violation exponent.Comment: LateX, 51 pages, 9 figures. (v2) References and comments added.
Misprints correcte
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
Characterising online museum users: a study of the National Museums Liverpool museum website
Museums are increasing access to their collections and providing richer user experiences via web-based interfaces. However, they are seeing high numbers of users looking at only one or two pages within 10 s and then leaving. To reduce this rate, a better understanding of the type of user who visits a museum website is required. Existing models for museum website users tend to focus on groups that are readily accessible for study or provide little detail in their definitions of the groups. This paper presents the results of a large-scale user survey for the National Museums Liverpool museum website in which data on a wide range of user characteristics were collected regarding their current visit to provide a better understanding of their motivations, tasks, engagement and domain knowledge. Results show that the frequently understudied general public and non-professional users make up the majority (approximately 77%) of the respondents
Academic Performance and Behavioral Patterns
Identifying the factors that influence academic performance is an essential
part of educational research. Previous studies have documented the importance
of personality traits, class attendance, and social network structure. Because
most of these analyses were based on a single behavioral aspect and/or small
sample sizes, there is currently no quantification of the interplay of these
factors. Here, we study the academic performance among a cohort of 538
undergraduate students forming a single, densely connected social network. Our
work is based on data collected using smartphones, which the students used as
their primary phones for two years. The availability of multi-channel data from
a single population allows us to directly compare the explanatory power of
individual and social characteristics. We find that the most informative
indicators of performance are based on social ties and that network indicators
result in better model performance than individual characteristics (including
both personality and class attendance). We confirm earlier findings that class
attendance is the most important predictor among individual characteristics.
Finally, our results suggest the presence of strong homophily and/or peer
effects among university students
Supersymmetry and Duality in Field Theory and String Theory
This is a set of lectures given at the 99' Cargese Summer School: Particle
Physics : Ideas and Recent Developments. They contain a pedestrian exposition
of recent theoretical progress in non-perturbative field theory and string
theory based on ideas of duality.Comment: JHEP LateX, 56 pages, 13 eps figures;v2 References adde
M-theory and Type IIA Flux Compactifications
We consider compactifications of M-theory and type IIA string theory to four
dimensions. For Minkowski space-time, a supergravity no-go theorem forbids flux
supported in the internal space. We show how to evade this no-go theorem by
exhibiting new sources of brane charge: in string theory, the basic physical
phenomenon is the generation of new brane charges from D-branes in transverse
fluxes. In M-theory, there is a new source of M5-brane charge from novel higher
derivative couplings that involve fluxes as well as curvatures. We present some
explicit orientifold examples with both N=1 and N=2 space-time supersymmetry.
Finally, we explain the status of massive type IIA flux compactifications.Comment: 36 pages, LaTeX; references adde
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