243 research outputs found
Fermions and noncommutative emergent gravity II: Curved branes in extra dimensions
We study fermions coupled to Yang-Mills matrix models from the point of view
of emergent gravity. The matrix model Dirac operator provides an appropriate
coupling for fermions to the effective gravitational metric for general branes
with nontrivial embedding, albeit with a non-standard spin connection. This
generalizes previous results for 4-dimensional matrix models. Integrating out
the fermions in a nontrivial geometrical background induces indeed the
Einstein-Hilbert action of the effective metric, as well as additional terms
which couple the Poisson tensor to the Riemann tensor, and a dilaton-like term.Comment: 34 pages; minor change
Matrix Models, Emergent Gravity, and Gauge Theory
Matrix models of Yang-Mills type induce an effective gravity theory on
4-dimensional branes, which are considered as models for dynamical space-time.
We review recent progress in the understanding of this emergent gravity. The
metric is not fundamental but arises effectively in the semi-classical limit,
along with nonabelian gauge fields. This leads to a mechanism for protecting
certain geometries from corrections due to the vacuum energy.Comment: 8 pages. Based on invited talks given at the Conferences "Quantum
Spacetime and Noncommutative Geometry", Rome, 2008 and at "Workshop on
quantum gravity and nocommutative geometry", Lisbon, 2008 and at "Emergent
Gravity", Boston, 2008 and at DICE2008, Italy, 2008 and at "QG2 2008 Quantum
Geometry and Quantum Gravity", Nottingham, 200
Curvature and Gravity Actions for Matrix Models
We show how gravitational actions, in particular the Einstein-Hilbert action,
can be obtained from additional terms in Yang-Mills matrix models. This is
consistent with recent results on induced gravitational actions in these matrix
models, realizing space-time as 4-dimensional brane solutions. It opens up the
possibility for a controlled non-perturbative description of gravity through
simple matrix models, with interesting perspectives for the problem of vacuum
energy. The relation with UV/IR mixing and non-commutative gauge theory is
discussed.Comment: 17 pages; v2+v3: minor correction
Schwarzschild Geometry Emerging from Matrix Models
We demonstrate how various geometries can emerge from Yang-Mills type matrix
models with branes, and consider the examples of Schwarzschild and
Reissner-Nordstroem geometry. We provide an explicit embedding of these branes
in R^{2,5} and R^{4,6}, as well as an appropriate Poisson resp. symplectic
structure which determines the non-commutativity of space-time. The embedding
is asymptotically flat with asymptotically constant \theta^{\mu\nu} for large
r, and therefore suitable for a generalization to many-body configurations.
This is an illustration of our previous work arXiv:1003.4132, where we have
shown how the Einstein-Hilbert action can be realized within such matrix
models.Comment: 21 pages, 1 figur
Covariant Field Equations, Gauge Fields and Conservation Laws from Yang-Mills Matrix Models
The effective geometry and the gravitational coupling of nonabelian gauge and
scalar fields on generic NC branes in Yang-Mills matrix models is determined.
Covariant field equations are derived from the basic matrix equations of
motions, known as Yang-Mills algebra. Remarkably, the equations of motion for
the Poisson structure and for the nonabelian gauge fields follow from a matrix
Noether theorem, and are therefore protected from quantum corrections. This
provides a transparent derivation and generalization of the effective action
governing the SU(n) gauge fields obtained in [1], including the would-be
topological term. In particular, the IKKT matrix model is capable of describing
4-dimensional NC space-times with a general effective metric. Metric
deformations of flat Moyal-Weyl space are briefly discussed.Comment: 31 pages. V2: minor corrections, references adde
Emergent Geometry and Gravity from Matrix Models: an Introduction
A introductory review to emergent noncommutative gravity within Yang-Mills
Matrix models is presented. Space-time is described as a noncommutative brane
solution of the matrix model, i.e. as submanifold of \R^D. Fields and matter on
the brane arise as fluctuations of the bosonic resp. fermionic matrices around
such a background, and couple to an effective metric interpreted in terms of
gravity. Suitable tools are provided for the description of the effective
geometry in the semi-classical limit. The relation to noncommutative gauge
theory and the role of UV/IR mixing is explained. Several types of geometries
are identified, in particular "harmonic" and "Einstein" type of solutions. The
physics of the harmonic branch is discussed in some detail, emphasizing the
non-standard role of vacuum energy. This may provide new approach to some of
the big puzzles in this context. The IKKT model with D=10 and close relatives
are singled out as promising candidates for a quantum theory of fundamental
interactions including gravity.Comment: Invited topical review for Classical and Quantum Gravity. 57 pages, 5
figures. V2,V3: minor corrections and improvements. V4,V5: some improvements,
refs adde
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Effectiveness of an antifungal stewardship programme at a London teaching hospital 2010–16
Background
The need for antifungal stewardship is gaining recognition with increasing incidence of invasive fungal infection (IFI) and antifungal resistance alongside the high cost of antifungal drugs. Following an audit showing suboptimal practice we initiated an antifungal stewardship programme and prospectively evaluated its impact on clinical and financial outcomes.
Patients and methods
From October 2010 to September 2016, adult inpatients receiving amphotericin B, echinocandins, intravenous fluconazole, flucytosine or voriconazole were reviewed weekly by an infectious diseases consultant and antimicrobial pharmacist. Demographics, diagnosis by European Organization for Research and Treatment of Cancer (EORTC) criteria, drug, indication, advice, acceptance and in-hospital mortality were recorded. Antifungal consumption and expenditure, and candidaemia species and susceptibility data were extracted from pharmacy and microbiology databases.
Results
A total of 432 patients were reviewed, most commonly receiving AmBisome® (35%) or intravenous fluconazole (29%). Empirical treatment was often unnecessary, with 82% having no evidence of IFI. Advice was given in 64% of reviews (most commonly de-escalating or stopping treatment) and was followed in 84%. Annual antifungal expenditure initially reduced by 30% (£0.98 million to £0.73 million), then increased to 20% above baseline over a 5 year period; this was a significantly lower rise compared with national figures, which showed a doubling of expenditure over the same period. Inpatient mortality, Candida species distribution and rates of resistance were not adversely affected by the intervention.
Conclusions
Provision of specialist input to optimize antifungal prescribing resulted in significant cost savings without compromising on microbiological or clinical outcomes. Our model is readily implementable by hospitals with high numbers of at-risk patients and antifungal expenditure
Gravity and compactified branes in matrix models
A mechanism for emergent gravity on brane solutions in Yang-Mills matrix
models is exhibited. Newtonian gravity and a partial relation between the
Einstein tensor and the energy-momentum tensor can arise from the basic matrix
model action, without invoking an Einstein-Hilbert-type term. The key
requirements are compactified extra dimensions with extrinsic curvature M^4 x K
\subset R^D and split noncommutativity, with a Poisson tensor \theta^{ab}
linking the compact with the noncompact directions. The moduli of the
compactification provide the dominant degrees of freedom for gravity, which are
transmitted to the 4 noncompact directions via the Poisson tensor. The
effective Newton constant is determined by the scale of noncommutativity and
the compactification. This gravity theory is well suited for quantization, and
argued to be perturbatively finite for the IKKT model. Since no
compactification of the target space is needed, it might provide a way to avoid
the landscape problem in string theory.Comment: 35 pages. V2: substantially revised and improved, conclusion
weakened. V3: some clarifications, published version. V4: minor correctio
Heat kernel expansion and induced action for matrix models
In this proceeding note, I review some recent results concerning the quantum
effective action of certain matrix models, i.e. the supersymmetric IKKT model,
in the context of emergent gravity. The absence of pathological UV/IR mixing is
discussed, as well as dynamical SUSY breaking and some relations with string
theory and supergravity.Comment: 11 pages, 1 figure; talk given at the 7th International Conference on
Quantum Theory and Symmetries, August 7-13, 2011, Prague/Czech Republi
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