3,152 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
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
Testing post-Newtonian theory with gravitational wave observations
The Laser Interferometric Space Antenna (LISA) will observe supermassive
black hole binary mergers with amplitude signal-to-noise ratio of several
thousands. We investigate the extent to which such observations afford
high-precision tests of Einstein's gravity. We show that LISA provides a unique
opportunity to probe the non-linear structure of post-Newtonian theory both in
the context of general relativity and its alternatives.Comment: 9 pages, 2 figure
Third post-Newtonian dynamics of compact binaries: Equations of motion in the center-of-mass frame
The equations of motion of compact binary systems and their associated
Lagrangian formulation have been derived in previous works at the third
post-Newtonian (3PN) approximation of general relativity in harmonic
coordinates. In the present work we investigate the binary's relative dynamics
in the center-of-mass frame (center of mass located at the origin of the
coordinates). We obtain the 3PN-accurate expressions of the center-of-mass
positions and equations of the relative binary motion. We show that the
equations derive from a Lagrangian (neglecting the radiation reaction), from
which we deduce the conserved center-of-mass energy and angular momentum at the
3PN order. The harmonic-coordinates center-of-mass Lagrangian is equivalent,
{\it via} a contact transformation of the particles' variables, to the
center-of-mass Hamiltonian in ADM coordinates that is known from the
post-Newtonian ADM-Hamiltonian formalism. As an application we investigate the
dynamical stability of circular binary orbits at the 3PN order.Comment: 31 pages, to appear in Classical and Quantum Gravit
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
Post-Newtonian approximation for isolated systems calculated by matched asymptotic expansions
Two long-standing problems with the post-Newtonian approximation for isolated
slowly-moving systems in general relativity are: (i) the appearance at high
post-Newtonian orders of divergent Poisson integrals, casting a doubt on the
soundness of the post-Newtonian series; (ii) the domain of validity of the
approximation which is limited to the near-zone of the source, and prevents
one, a priori, from incorporating the condition of no-incoming radiation, to be
imposed at past null infinity. In this article, we resolve the problem (i) by
iterating the post-Newtonian hierarchy of equations by means of a new
(Poisson-type) integral operator that is free of divergencies, and the problem
(ii) by matching the post-Newtonian near-zone field to the exterior field of
the source, known from previous work as a multipolar-post-Minkowskian expansion
satisfying the relevant boundary conditions at infinity. As a result, we obtain
an algorithm for iterating the post-Newtonian series up to any order, and we
determine the terms, present in the post-Newtonian field, that are associated
with the gravitational-radiation reaction onto an isolated slowly-moving matter
system.Comment: 61 pages, to appear in Phys. Rev.
Leptogenesis with exclusively low-energy CP Violation in the Context of Minimal Lepton Flavour Violation
We analyze lepton flavour violation (LFV) and the generation of the observed
baryon-antibaryon asymmetry of the Universe (BAU) within a generalized minimal
lepton flavour violation framework with three quasi-degenerate heavy Majorana
neutrinos. The BAU which is obtained through radiative resonant leptogenesis
can successfully be generated widely independent of the Majorana scale in this
scenario and flavour effects are found to be relevant. Then we discuss the
specific case in which CP violation is exclusively present at low-energies (a
real R matrix) in the flavour sensitive temperature regime. Successful
leptogenesis in this case leads to strong constraints on low-energy neutrino
parameters.Comment: Contrubution to the proceedings of the EPS HEP 2007 conference,
Manchester (UK). 3 pages, 3 figure
Gravitational radiation reaction in the equations of motion of compact binaries to 3.5 post-Newtonian order
We compute the radiation reaction force on the orbital motion of compact
binaries to the 3.5 post-Newtonian (3.5PN) approximation, i.e. one PN order
beyond the dominant effect. The method is based on a direct PN iteration of the
near-zone metric and equations of motion of an extended isolated system, using
appropriate ``asymptotically matched'' flat-space-time retarded potentials. The
formalism is subsequently applied to binary systems of point particles, with
the help of the Hadamard self-field regularisation. Our result is the 3.5PN
acceleration term in a general harmonic coordinate frame. Restricting the
expression to the centre-of-mass frame, we find perfect agreement with the
result derived in a class of coordinate systems by Iyer and Will using the
energy and angular momentum balance equations.Comment: 28 pages, references added, to appear in Classical and Quantum
Gravit
Post-ISCO Ringdown Amplitudes in Extreme Mass Ratio Inspiral
An extreme mass ratio inspiral consists of two parts: adiabatic inspiral and
plunge. The plunge trajectory from the innermost stable circular orbit (ISCO)
is special (somewhat independent of initial conditions). We write an expression
for its solution in closed-form and for the emitted waveform. In particular we
extract an expression for the associated black-hole ringdown amplitudes, and
evaluate them numerically.Comment: 21 pages, 5 figures. v4: added section with numerical evaluation of
the ringdown amplitude
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