1,026 research outputs found
Uniformly accelerating black holes in a de Sitter universe
A class of exact solutions of Einstein's equations is analysed which
describes uniformly accelerating charged black holes in an asymptotically de
Sitter universe. This is a generalisation of the C-metric which includes a
cosmological constant. The physical interpretation of the solutions is
facilitated by the introduction of a new coordinate system for de Sitter space
which is adapted to accelerating observers in this background. The solutions
considered reduce to this form of the de Sitter metric when the mass and charge
of the black holes vanish.Comment: 6 pages REVTeX, 3 figures, to appear in Phys. Rev. D. Figure 2
correcte
Hirota's Solitons in the Affine and the Conformal Affine Toda Models
We use Hirota's method formulated as a recursive scheme to construct complete
set of soliton solutions for the affine Toda field theory based on an arbitrary
Lie algebra. Our solutions include a new class of solitons connected with two
different type of degeneracies encountered in the Hirota's perturbation
approach. We also derive an universal mass formula for all Hirota's solutions
to the Affine Toda model valid for all underlying Lie groups. Embedding of the
Affine Toda model in the Conformal Affine Toda model plays a crucial role in
this analysis.Comment: 36 pages, LaTe
Nuttier Bubbles
We construct new explicit solutions of general relativity from double
analytic continuations of Taub-NUT spacetimes. This generalizes previous
studies of 4-dimensional nutty bubbles. One 5-dimensional locally
asymptotically AdS solution in particular has a special conformal boundary
structure of . We compute its boundary stress tensor and
relate it to the properties of the dual field theory. Interestingly enough, we
also find consistent 6-dimensional bubble solutions that have only one timelike
direction. The existence of such spacetimes with non-trivial topology is
closely related to the existence of the Taub-NUT(-AdS) solutions with more than
one NUT charge. Finally, we begin an investigation of generating new solutions
from Taub-NUT spacetimes and nuttier bubbles. Using the so-called Hopf duality,
we provide new explicit time-dependent backgrounds in six dimensions.Comment: 32 pages, 1 figure; v.3. typos corrected. Matches the published
versio
On Hexagonal Structures in Higher Dimensional Theories
We analyze the geometrical background under which many Lie groups relevant to
particle physics are endowed with a (possibly multiple) hexagonal structure.
There are several groups appearing, either as special holonomy groups on the
compactification process from higher dimensions, or as dynamical string gauge
groups; this includes groups like SU(2),SU(3), G_2, Spin(7), SO(8) as well as
E_8 and SO(32). We emphasize also the relation of these hexagonal structures
with the octonion division algebra, as we expect as well eventually some role
for octonions in the interpretation of symmetries in High Energy Physics.Comment: 9 pages, Latex, 3 figures. Accepted for publication in International
Journal of Theoretical Physic
Pair of accelerated black holes in a de Sitter background: the dS C-metric
Following the work of Kinnersley and Walker for flat spacetimes, we have
analyzed the anti-de Sitter C-metric in a previous paper. In the de Sitter
case, Podolsky and Griffiths have established that the de Sitter C-metric (dS
C-metric) found by Plebanski and Demianski describes a pair of accelerated
black holes in the dS background with the acceleration being provided (in
addition to the cosmological constant) by a strut that pushes away the two
black holes or, alternatively, by a string that pulls them. We extend their
analysis mainly in four directions. First, we draw the Carter-Penrose diagrams
of the massless uncharged dS C-metric, of the massive uncharged dS C-metric and
of the massive charged dS C-metric. These diagrams allow us to clearly identify
the presence of two dS black holes and to conclude that they cannot interact
gravitationally. Second, we revisit the embedding of the dS C-metric in the 5D
Minkowski spacetime and we represent the motion of the dS C-metric origin in
the dS 4-hyperboloid as well as the localization of the strut. Third, we
comment on the physical properties of the strut that connects the two black
holes. Finally, we find the range of parameters that correspond to non-extreme
black holes, extreme black holes, and naked particles.Comment: 11 pages, 11 figures (RevTeX4). Published version: references adde
Neutrino masses from higher than d=5 effective operators
We discuss the generation of small neutrino masses from effective operators
higher than dimension five, which open new possibilities for low scale see-saw
mechanisms. In order to forbid the radiative generation of neutrino mass by
lower dimensional operators, extra fields are required, which are charged under
a new symmetry. We discuss this mechanism in the framework of a two Higgs
doublet model. We demonstrate that the tree level generation of neutrino mass
from higher dimensional operators often leads to inverse see-saw scenarios in
which small lepton number violating terms are naturally suppressed by the new
physics scale. Furthermore, we systematically discuss tree level
generalizations of the standard see-saw scenarios from higher dimensional
operators. Finally, we point out that higher dimensional operators can also be
generated at the loop level. In this case, we obtain the TeV scale as new
physics scale even with order one couplings.Comment: 22 pages, 3 figures, 2 tables. Some references adde
Doctors’ recognition and management of melanoma patients’ risk: an Australian population-based study
Background Guidelines recommend that health professionals identify and manage individuals at high risk of developing melanoma, but there is limited population-based evidence demonstrating real-world practices. Objective A population-based, observational study was conducted in the state of New South Wales, Australia to determine doctors’ knowledge of melanoma patients’ risk and to identify factors associated with better identification and clinical management. Methods Data were analysed for 1889 patients with invasive, localised melanoma in the Melanoma Patterns of Care study. This study collected data on all melanoma diagnoses notified to the state’s cancer registry during a 12-month period from 2006 to 2007, as well as questionnaire data from the doctors involved in their care. Results Three-quarters (74%) of patients had doctors who were aware of their risk factor status with respect to personal and family history of melanoma and the presence of many moles. Doctors working in general practice, skin cancer clinics and dermatology settings had better knowledge of patients’ risk factors than plastic surgeons. Doctors were 15% more likely to know the family history of younger melanoma patients (<40 years) than of those ≥80 years (95% confidence interval 4–26%). Early detection-related follow-up advice was more likely to be given to younger patients, by doctors aware of their patients’ risk status, by doctors practising in plastic surgery, dermatology and skin cancer clinic settings, and by female doctors. Conclusion Both patient-related and doctor-related factors were associated with doctors’ recognition and management of melanoma patients’ risk and could be the focus of strategies for improving care
Low energy effects of neutrino masses
While all models of Majorana neutrino masses lead to the same dimension five
effective operator, which does not conserve lepton number, the dimension six
operators induced at low energies conserve lepton number and differ depending
on the high energy model of new physics. We derive the low-energy dimension six
operators which are characteristic of generic Seesaw models, in which neutrino
masses result from the exchange of heavy fields which may be either fermionic
singlets, fermionic triplets or scalar triplets. The resulting operators may
lead to effects observable in the near future, if the coefficients of the
dimension five and six operators are decoupled along a certain pattern, which
turns out to be common to all models. The phenomenological consequences are
explored as well, including their contributions to and new
bounds on the Yukawa couplings for each model.Comment: modifications: couplings in appendix B, formulas (121)-(122) on rare
leptons decays (to match with published version) and consequently bounds in
table
Cosmological Black Holes on Branes
We examined analytically a cosmological black hole domain wall system. Using
the C-metric construction we derived the metric for the spacetime describing an
infinitely thin domain wall intersecting a cosmological black hole. We studied
the behaviour of the scalar field describing a self-interacting cosmological
domain wall and find the approximated solution valid for large distances. The
thin wall approximation and the back raection problem were elaborated finding
that the topological kink solution smoothed out singular behaviour of the zero
thickness wall using a core topological and hence thick domain wall. We also
analyze the nucleation of cosmological black holes on and in the presence of a
domain walls and conclude that the domain wall will nucleate small black holes
on it rather than large ones inside.Comment: 13 pages, Revtex, to be published in Phys.Rev. D1
The extremal limits of the C-metric: Nariai, Bertotti-Robinson and anti-Nariai C-metrics
In two previous papers we have analyzed the C-metric in a background with a
cosmological constant, namely the de Sitter (dS) C-metric, and the anti-de
Sitter (AdS) C-metric, following the work of Kinnersley and Walker for the flat
C-metric. These exact solutions describe a pair of accelerated black holes in
the flat or cosmological constant background, with the acceleration A being
provided by a strut in-between that pushes away the two black holes. In this
paper we analyze the extremal limits of the C-metric in a background with
generic cosmological constant. We follow a procedure first introduced by
Ginsparg and Perry in which the Nariai solution, a spacetime which is the
direct topological product of the 2-dimensional dS and a 2-sphere, is generated
from the four-dimensional dS-Schwarzschild solution by taking an appropriate
limit, where the black hole event horizon approaches the cosmological horizon.
Similarly, one can generate the Bertotti-Robinson metric from the
Reissner-Nordstrom metric by taking the limit of the Cauchy horizon going into
the event horizon of the black hole, as well as the anti-Nariai by taking an
appropriate solution and limit. Using these methods we generate the C-metric
counterparts of the Nariai, Bertotti-Robinson and anti-Nariai solutions, among
others. One expects that the solutions found in this paper are unstable and
decay into a slightly non-extreme black hole pair accelerated by a strut or by
strings. Moreover, the Euclidean version of these solutions mediate the quantum
process of black hole pair creation, that accompanies the decay of the dS and
AdS spaces
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