284 research outputs found
Renormalizability of Massive Gravity in Three Dimensions
We discuss renormalizability of a recently established, massive gravity
theory with particular higher derivative terms in three space-time dimensions.
It is shown that this massive gravity is certainly renormalizable as well as
unitary, so it gives us a physically interesting toy model of perturbative
quantum gravity in three dimensions.Comment: 13 pages, no figure
Three-dimensional black holes, gravitational solitons, kinks and wormholes for BHT massive gravity
The theory of massive gravity in three dimensions recently proposed by
Bergshoeff, Hohm and Townsend (BHT) is considered. At the special case when the
theory admits a unique maximally symmetric solution, a conformally flat space
that contains black holes and gravitational solitons for any value of the
cosmological constant is found. For negative cosmological constant, the black
hole is characterized in terms of the mass and the "gravitational hair"
parameter, providing a lower bound for the mass. For negative mass parameter,
the black hole acquires an inner horizon, and the entropy vanishes at the
extremal case. Gravitational solitons and kinks, being regular everywhere, are
obtained from a double Wick rotation of the black hole. A wormhole solution in
vacuum that interpolates between two static universes of negative spatial
curvature is obtained as a limiting case of the gravitational soliton with a
suitable identification. The black hole and the gravitational soliton fit
within a set of relaxed asymptotically AdS conditions as compared with the ones
of Brown and Henneaux. In the case of positive cosmological constant the black
hole possesses an event and a cosmological horizon, whose mass is bounded from
above. Remarkably, the temperatures of the event and the cosmological horizons
coincide, and at the extremal case one obtains the analogue of the Nariai
solution, . A gravitational soliton is also obtained
through a double Wick rotation of the black hole. The Euclidean continuation of
these solutions describes instantons with vanishing Euclidean action. For
vanishing cosmological constant the black hole and the gravitational soliton
are asymptotically locally flat spacetimes. The rotating solutions can be
obtained by boosting the previous ones in the plane.Comment: Talk given at the "Workshop on Gravity in Three Dimensions," 14-24
April 2009, ESI, Vienna. 30 pages, 6 figures. V2: minor changes and section 6
slightly improved. Last version for JHE
Risk perception, safer sex practices and PrEP enthusiasm: Barriers and facilitators to oral HIV pre-exposure prophylaxis in Black African and Black Caribbean women in the UK
Objectives: UK Black African/Black Caribbean women remain disproportionately affected by HIV. Although oral pre-exposure prophylaxis (PrEP) could offer them an effective HIV prevention method, uptake remains limited. This study examined barriers and facilitators to PrEP awareness and candidacy perceptions for Black African/Black Caribbean women to help inform PrEP programmes and service development. Methods: Using purposive sampling through community organisations, 32 in-depth, semi-structured interviews were conducted with Black African/Black Caribbean women living in London and Glasgow between June and August 2018. Participants (aged 19–63) included women of varied HIV statuses to explore perceptions of sexual risk and safer sex, sexual health knowledge and PrEP attitudes. A thematic analysis guided by the Social Ecological Model was used to explore how PrEP perceptions intersected with wider safer sex understandings and practices. Results: Four key levels of influence shaping safer sex notions and PrEP candidacy perceptions emerged: personal, interpersonal, perceived environment and policy. PrEP-specific knowledge was low and some expressed distrust in PrEP. Many women were enthusiastic about PrEP for others but did not situate PrEP within their own safer sex understandings, sometimes due to difficulty assessing their own HIV risk. Many felt that PrEP could undermine intimacy in their relationships by disrupting the shared responsibility implicit within other HIV prevention methods. Women described extensive interpersonal networks that supported their sexual health knowledge and shaped their interactions with health services, though these networks were influenced by prevailing community stigmas. Conclusions: Difficulty situating PrEP within existing safer sex beliefs contributes to limited perceptions of personal PrEP candidacy. To increase PrEP uptake in UK Black African/Black Caribbean women, interventions will need to enable women to advance their knowledge of PrEP within the broader context of their sexual health and relationships. PrEP service models will need to include trusted ‘non-sexual health-specific’ community services such as general practice
Harnessing the immune system in the battle against breast cancer
Breast cancer is the most prevalent malignancy in women and the second most common cause of cancer-related death worldwide. Despite major innovations in early detection and advanced therapeutics, up to 30% of women with nodenegative breast cancer and 70% of women with node-positive breast cancer will develop recurrence. The recognition that breast tumors are infiltrated by a complex array of immune cells that influence their development, progression, and metastasis, as well as their responsiveness to systemic therapies has sparked major interest in the development of immunotherapies. In fact, not only the native host immune system can be altered to promote potent antitumor response, but also its components can be manipulated to generate effective therapeutic strategies. We present here a review of the major approaches to immunotherapy in breast cancers, both successes and failures, as well as new therapies on the horizon
Discussing Quantum Aspects of Higher-Derivative 3D-Gravity in the First-Order Formalism
In this paper, we reassess the issue of deriving the propagators and
identifying the spectrum of excitations associated to the vielbein and spin
connection of (1+2)-D gravity in the presence of dynamical torsion, while
working in the first-order formulation. A number of peculiarities is pointed
out whenever the Chern-Simons term is taken into account along with a
combination of bilinear terms in the torsion tensor. We present a procedure to
derive the full set of propagators, based on an algebra of enlarged spin-type
operators, and we discuss under which conditions the poles of the tree-level
2-point functions correspond to physical excitations that do not conflict with
causality and unitarity
A Complete Classification of Higher Derivative Gravity in 3D and Criticality in 4D
We study the condition that the theory is unitary and stable in
three-dimensional gravity with most general quadratic curvature,
Lorentz-Chern-Simons and cosmological terms. We provide the complete
classification of the unitary theories around flat Minkowski and (anti-)de
Sitter spacetimes. The analysis is performed by examining the quadratic
fluctuations around these classical vacua. We also discuss how to understand
critical condition for four-dimensional theories at the Lagrangian level.Comment: 20 pages, v2: minor corrections, refs. added, v3: logic modified, v4:
typos correcte
On the new massive gravity and AdS/CFT
Demanding the existence of a simple holographic -theorem, it is shown that
a general (parity preserving) theory of gravity in 2+1 dimensions involving
upto four derivative curvature invariants reduces to the new massive gravity
theory. We consider extending the theory including upto six derivative
curvature invariants. Black hole solutions are presented and consistency with
1+1 CFTs is checked. We present evidence that bulk unitarity is still in
conflict with a positive CFT central charge for generic choice of parameters.
However, for a special choice of parameters appearing in the four and six
derivative terms reduces the linearized equations to be two derivative, thereby
ameliorating the unitarity problem.Comment: 16 pages, 2 figures. v4: typo correcte
Hamiltonian analysis of BHT massive gravity
We study the Hamiltonian structure of the Bergshoeff-Hohm-Townsend (BHT)
massive gravity with a cosmological constant. In the space of coupling
constants , our canonical analysis reveals the special role of
the condition . In this sector, the dimension of the
physical phase space is found to be , which corresponds to two
Lagrangian degree of freedom. When applied to the AdS asymptotic region, the
canonical approach yields the conserved charges of the BTZ black hole, and
central charges of the asymptotic symmetry algebra.Comment: LATEX, 21 pages; v2: minor correction
Note on New Massive Gravity in
In this note we study the properties of linearized gravitational excitations
in the new massive gravity theory in asymptotically spacetime and find
that there is also a critical point for the mass parameter at which massive
gravitons become massless as in topological massive gravity in .
However, at this critical point in the new massive gravity the energy of all
branches of highest weight gravitons vanish and the central charges also vanish
within the Brown-Henneaux boundary conditions. The new massive gravity in
asymptotically spacetime seems to be trivial at this critical point
under the Brown-Henneaux boundary conditions if the Brown-Henneaux boundary
conditions can be consistent with this theory. At this point, the boundary
conditions of log gravity may be preferred.Comment: v3 typos corrected, refs added, version to appear in JHE
- …