2,501 research outputs found
Dirac phase leptogenesis
I present here a concise summary of the preprint arXiv:0707.3024, written in
collaboration with A. Anisimov and P. Di Bari. There we discuss leptogenesis
when {\em CP} violation stems exlusively from the Dirac phase in the PMNS
mixing matrix. Under this assumption it turns out that the situation is very
constrained when a hierarchical heavy right-handed (RH) neutrino spectrum is
considered: the allowed regions are small and the final asymmetry depends on
the initial conditions. On the other hand, for a quasi-degenerate spectrum of
RH neutrinos, the {\em CP} asymmetry can be enhanced and the situation becomes
much more favorable, with no dependence on the initial conditions.
Interestingly, in the extreme case of resonant leptogenesis, in order to match
the observed baryon asymmetry of the Universe, we obtain a lower bound on \sin
\q_{13} which depends on the lightest active neutrino mass m_1.Comment: 3 pages, 2 figures, contribution to the proceedings of the TAUP 07
conference, Sep. 11-15, Sendai, Japa
Gravitational-Wave Inspiral of Compact Binary Systems to 7/2 Post-Newtonian Order
The inspiral of compact binaries, driven by gravitational-radiation reaction,
is investigated through 7/2 post-Newtonian (3.5PN) order beyond the quadrupole
radiation. We outline the derivation of the 3.5PN-accurate binary's
center-of-mass energy and emitted gravitational flux. The analysis consistently
includes the relativistic effects in the binary's equations of motion and
multipole moments, as well as the contributions of tails, and tails of tails,
in the wave zone. However the result is not fully determined because of some
physical incompleteness, present at the 3PN order, of the model of
point-particle and the associated Hadamard-type self-field regularization. The
orbital phase, whose prior knowledge is crucial for searching and analyzing the
inspiral signal, is computed from the standard energy balance argument.Comment: 12 pages, version which includes the correction of an Erratum to be
published in Phys. Rev. D (2005
On the Role of Low-Energy CP Violation in Leptogenesis
The link between low-energy CP violation and leptogenesis became more
accessible with the understanding of flavor effects. However, a definite
well-motivated model where such a link occurs was still lacking. Adjoint SU(5)
is a simple grand unified theory where neutrino masses are generated through
the Type I and Type III seesaw mechanisms, and the lepton asymmetry is
generated by the fermionic triplet responsible for the Type III seesaw. We
focus exclusively on the case of inverted hierarchy for neutrinos, and we show
that successful flavored leptogenesis in this theory strongly points towards
low-energy CP violation. Moreover, since the range of allowed masses for the
triplet is very restricted, we find that the discovery at the LHC of new states
present in the theory, together with proton decay and unification of gauge
couplings, can conspire to provide a hint in favor of leptogenesis.Comment: 12 pages, 6 figure
Health systems analysis of eye care services in Zambia: evaluating progress towards VISION 2020 goals.
BACKGROUND: VISION 2020 is a global initiative launched in 1999 to eliminate avoidable blindness by 2020. The objective of this study was to undertake a situation analysis of the Zambian eye health system and assess VISION 2020 process indicators on human resources, equipment and infrastructure. METHODS: All eye health care providers were surveyed to determine location, financing sources, human resources and equipment. Key informants were interviewed regarding levels of service provision, management and leadership in the sector. Policy papers were reviewed. A health system dynamics framework was used to analyse findings. RESULTS: During 2011, 74 facilities provided eye care in Zambia; 39% were public, 37% private for-profit and 24% owned by Non-Governmental Organizations. Private facilities were solely located in major cities. A total of 191 people worked in eye care; 18 of these were ophthalmologists and eight cataract surgeons, equivalent to 0.34 and 0.15 per 250,000 population, respectively. VISION 2020 targets for inpatient beds and surgical theatres were met in six out of nine provinces, but human resources and spectacles manufacturing workshops were below target in every province. Inequalities in service provision between urban and rural areas were substantial. CONCLUSION: Shortage and maldistribution of human resources, lack of routine monitoring and inadequate financing mechanisms are the root causes of underperformance in the Zambian eye health system, which hinder the ability to achieve the VISION 2020 goals. We recommend that all VISION 2020 process indicators are evaluated simultaneously as these are not individually useful for monitoring progress
Gravitational waves from black hole binary inspiral and merger: The span of third post-Newtonian effective-one-body templates
We extend the description of gravitational waves emitted by binary black
holes during the final stages of inspiral and merger by introducing in the
third post-Newtonian (3PN) effective-one-body (EOB) templates seven new
``flexibility'' parameters that affect the two-body dynamics and gravitational
radiation emission. The plausible ranges of these flexibility parameters,
notably the parameter characterising the fourth post-Newtonian effects in the
dynamics, are estimated. Using these estimates, we show that the currently
available standard 3PN bank of EOB templates does ``span'' the space of signals
opened up by all the flexibility parameters, in that their maximized mutual
overlaps are larger than 96.5%. This confirms the effectualness of 3PN EOB
templates for the detection of binary black holes in gravitational-wave data
from interferometric detectors. The possibility to drastically reduce the
number of EOB templates using a few ``universal'' phasing functions is
suggested.Comment: 23 pages, 3 figures, 4 tables, with revtex4, Minor clarifications,
Final published versio
Tail-induced spin-orbit effect in the gravitational radiation of compact binaries
Gravitational waves contain tail effects which are due to the back-scattering
of linear waves in the curved space-time geometry around the source. In this
paper we improve the knowledge and accuracy of the two-body inspiraling
post-Newtonian (PN) dynamics and gravitational-wave signal by computing the
spin-orbit terms induced by tail effects. Notably, we derive those terms at 3PN
order in the gravitational-wave energy flux, and 2.5PN and 3PN orders in the
wave polarizations. This is then used to derive the spin-orbit tail effects in
the phasing through 3PN order. Our results can be employed to carry out more
accurate comparisons with numerical-relativity simulations and to improve the
accuracy of analytical templates aimed at describing the whole process of
inspiral, merger and ringdown.Comment: Minor corrections. To be published in Physical Review
Time-symmetric initial data for binary black holes in numerical relativity
We look for physically realistic initial data in numerical relativity which
are in agreement with post-Newtonian approximations. We propose a particular
solution of the time-symmetric constraint equation, appropriate to two
momentarily static black holes, in the form of a conformal decomposition of the
spatial metric. This solution is isometric to the post-Newtonian metric up to
the 2PN order. It represents a non-linear deformation of the solution of Brill
and Lindquist, i.e. an asymptotically flat region is connected to two
asymptotically flat (in a certain weak sense) sheets, that are the images of
the two singularities through appropriate inversion transformations. The total
ADM mass M as well as the individual masses m_1 and m_2 (when they exist) are
computed by surface integrals performed at infinity. Using second order
perturbation theory on the Brill-Lindquist background, we prove that the
binary's interacting mass-energy M-m_1-m_2 is well-defined at the 2PN order and
in agreement with the known post-Newtonian result.Comment: 27 pages, to appear in Phys. Rev.
Innermost circular orbit of binary black holes at the third post-Newtonian approximation
The equations of motion of two point masses have recently been derived at the
3PN approximation of general relativity. From that work we determine the
location of the innermost circular orbit or ICO, defined by the minimum of the
binary's 3PN energy as a function of the orbital frequency for circular orbits.
We find that the post-Newtonian series converges well for equal masses. Spin
effects appropriate to corotational black-hole binaries are included. We
compare the result with a recent numerical calculation of the ICO in the case
of two black holes moving on exactly circular orbits (helical symmetry). The
agreement is remarkably good, indicating that the 3PN approximation is adequate
to locate the ICO of two black holes with comparable masses. This conclusion is
reached with the post-Newtonian expansion expressed in the standard Taylor
form, without using resummation techniques such as Pad\'e approximants and/or
effective-one-body methods.Comment: 21 pages, to appear in Phys. Rev. D (spin effects appropriate to
corotational black-hole binaries are included; discussion on the validity of
the approximation is added
Minimal Lepton Flavour Violation and Leptogenesis with exclusively low-energy CP Violation
We study the implications of a successful leptogenesis within the framework
of Minimal Lepton Flavour Violation combined with radiative resonant
leptogenesis and the PMNS matrix being the only source of CP violation, which
can be obtained provided flavour effects are taken into account. We find that
the right amount of the baryon asymmetry of the universe can be generated under
the conditions of a normal hierarchy of the light neutrino masses, a
non-vanishing Majorana phase, sin(theta_{13})>0.13 and m_{nu,lightest}<0.04 eV.
If this is fulfilled, we find strong correlations among ratios of charged LFV
processes.Comment: published in JHEP, small change
The Statistical Mechanics of Horizons and Black Hole Thermodynamics
Although we know that black holes are characterized by a temperature and an
entropy, we do not yet have a satisfactory microscopic ``statistical
mechanical'' explanation for black hole thermodynamics. I describe a new
approach that attributes the thermodynamic properties to ``would-be gauge''
degrees of freedom that become dynamical on the horizon. For the
(2+1)-dimensional black hole, this approach gives the correct entropy. (Talk
given at the Pacific Conference on Gravitation and Cosmology, Seoul, February
1996.)Comment: 11 pages, LaTe
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