4,270 research outputs found
Renormalization of the Non-Linear Sigma Model in Four Dimensions. A two-loop example
The renormalization procedure of the non-linear SU(2) sigma model in D=4
proposed in hep-th/0504023 and hep-th/0506220 is here tested in a truly
non-trivial case where the non-linearity of the functional equation is crucial.
The simplest example, where the non-linear term contributes, is given by the
two-loop amplitude involving the insertion of two \phi_0 (the constraint of the
non-linear sigma model) and two flat connections. In this case we verify the
validity of the renormalization procedure: the recursive subtraction of the
pole parts at D=4 yields amplitudes that satisfy the defining functional
equation. As a by-product we give a formal proof that in D dimensions (without
counterterms) the Feynman rules provide a perturbative symmetric solution.Comment: Latex, 3 figures, 19 page
Low latency search for Gravitational waves from BH-NS binaries in coincidence with Short Gamma Ray Bursts
We propose a procedure to be used in the search for gravitational waves from
black hole-neutron star coalescing binaries, in coincidence with short
gamma-ray bursts. It is based on two recently proposed semi-analytic fits, one
reproducing the mass of the remnant disk surrounding the black hole which forms
after the merging as a function of some binary parameters, the second relating
the neutron star compactness, i.e. the ratio of mass and radius, with its tidal
deformability. Using a Fisher matrix analysis and the two fits, we assign a
probability that the emitted gravitational signal is associated to the
formation of an accreting disk massive enough to supply the energy needed to
power a short gamma ray burst. This information can be used in low-latency data
analysis to restrict the parameter space searching for gravitational wave
signals in coincidence with short gamma-ray bursts, and to gain information on
the dynamics of the coalescing system and on the internal structure of the
components. In addition, when the binary parameters will be measured with high
accuracy, it will be possible to use this information to trigger the search for
off-axis gamma-ray bursts afterglows.Comment: 5 pages, 1 figure, changes in the introduction and in the concluding
remarks. Accepted for publication in Phys. Rev.
Direct Algebraic Restoration of Slavnov-Taylor Identities in the Abelian Higgs-Kibble Model
A purely algebraic method is devised in order to recover Slavnov-Taylor
identities (STI), broken by intermediate renormalization. The counterterms are
evaluated order by order in terms of finite amplitudes computed at zero
external momenta. The evaluation of the breaking terms of the STI is avoided
and their validity is imposed directly on the vertex functional. The method is
applied to the abelian Higgs-Kibble model. An explicit mass term for the gauge
field is introduced, in order to check the relevance of nilpotency. We show
that, since there are no anomalies, the imposition of the STI turns out to be
equivalent to the solution of a linear problem. The presence of ST invariants
implies that there are many possible solutions, corresponding to different
normalization conditions. Moreover, we find more equations than unknowns
(over-determined problem). This leads us to the consideration of consistency
conditions, that must be obeyed if the restoration of STI is possible.Comment: 10 pages, Latex and packages amsfonts, amssymb and amsth
Constraining the equation of state of nuclear matter with gravitational wave observations: Tidal deformability and tidal disruption
We study how to extract information on the neutron star equation of state
from the gravitational wave signal emitted during the coalescence of a binary
system composed of two neutron stars or a neutron star and a black hole. We use
post-Newtonian templates which include the tidal deformability parameter and,
when tidal disruption occurs before merger, a frequency cut-off. Assuming that
this signal is detected by Advanced LIGO/Virgo or ET, we evaluate the
uncertainties on these parameters using different data analysis strategies
based on the Fisher matrix approach, and on recently obtained analytical fits
of the relevant quantities. We find that the tidal deformability is more
effective than the stellar compactness to discriminate among different possible
equations of state.Comment: 13 pages, 4 figures, 4 tables. Minor changes to match the version
appearing on Phys. Rev.
Solving the relativistic inverse stellar problem through gravitational waves observation of binary neutron stars
The LIGO/Virgo collaboration has recently announced the direct detection of
gravitational waves emitted in the coalescence of a neutron star binary. This
discovery allows, for the first time, to set new constraints on the behavior of
matter at supranuclear density, complementary with those coming from
astrophysical observations in the electromagnetic band. In this paper we
demonstrate the feasibility of using gravitational signals to solve the
relativistic inverse stellar problem, i.e. to reconstruct the parameters of the
equation of state (EoS) from measurements of the stellar mass and tidal Love
number. We perform Bayesian inference of mock data, based on different models
of the star internal composition, modeled through piecewise polytropes. Our
analysis shows that the detection of a small number of sources by a network of
advanced interferometers would allow to put accurate bounds on the EoS
parameters, and to perform a model selection among the realistic equations of
state proposed in the literature.Comment: minor changes to match the version published on PR
Rotating proto-neutron stars: spin evolution, maximum mass and I-Love-Q relations
Shortly after its birth in a gravitational collapse, a proto-neutron star
enters in a phase of quasi-stationary evolution characterized by large
gradients of the thermodynamical variables and intense neutrino emission. In
few tens of seconds the gradients smooth out while the star contracts and cools
down, until it becomes a neutron star. In this paper we study this phase of the
proto-neutron star life including rotation, and employing finite temperature
equations of state. We model the evolution of the rotation rate, and determine
the relevant quantities characterizing the star. Our results show that an
isolated neutron star cannot reach, at the end of the evolution, the maximum
values of mass and rotation rate allowed by the zero-temperature equation of
state. Moreover, a mature neutron star evolved in isolation cannot rotate too
rapidly, even if it is born from a proto-neutron star rotating at the
mass-shedding limit. We also show that the I-Love-Q relations are violated in
the first second of life, but they are satisfied as soon as the entropy
gradients smooth out.Comment: 15 pages, 9 figures, 7 tables; minor changes, and extended discussion
on the I-Love-Q relation
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