4,408 research outputs found
A new approach to the analysis of the phase space of f(R)-gravity
We propose a new dynamical system formalism for the analysis of f(R)
cosmologies. The new approach eliminates the need for cumbersome inversions to
close the dynamical system and allows the analysis of the phase space of
f(R)-gravity models which cannot be investigated using the standard technique.
Differently form previously proposed similar techniques, the new method is
constructed in such a way to associate to the fixed points scale factors, which
contain four integration constants (i.e. solutions of fourth order differential
equations). In this way a new light is shed on the physical meaning of the
fixed points. We apply this technique to some f(R) Lagrangians relevant for
inflationary and dark energy models.Comment: 32 pages, 13 figures, typos corrected, updated bibliograph
Covariant gauge invariant theory of Scalar Perturbations in -gravity: a brief review
I review the state of the art of the investigation on the structure formation
in -gravity based on the Covariant and Gauge Invariant approach to
perturbations. A critical analysis of the results, in particular the presence
of characteristic signature of these models, together with their meaning and
their implication is given.Comment: 23 pages, 12 figures, to appear on The Open Astronomy Journa
A first-order secular theory for the post-Newtonian two-body problem with spin -- I: The restricted case
We revisit the relativistic restricted two-body problem with spin employing a
perturbation scheme based on Lie series. Starting from a post-Newtonian
expansion of the field equations, we develop a first-order secular theory that
reproduces well-known relativistic effects such as the precession of the
pericentre and the Lense-Thirring and geodetic effects. Additionally, our
theory takes into full account the complex interplay between the various
relativistic effects, and provides a new explicit solution of the averaged
equations of motion in terms of elliptic functions. Our analysis reveals the
presence of particular configurations for which non-periodical behaviour can
arise. The application of our results to real astrodynamical systems (such as
Mercury-like and pulsar planets) highlights the contribution of relativistic
effects to the long-term evolution of the spin and orbit of the secondary body.Comment: 14 pages, 3 figures, Published in MNRA
On the Anisotropic Interior Solutions in Ho\v{r}ava Gravity and Einstein-{\ae}ther Theory
We find a reconstruction algorithm able to generate all the static
spherically symmetric interior solutions in the framework of Ho\v{r}ava gravity
and Einstein-\ae ther theory in presence of anisotropic fluids. We focus for
simplicity on the case of a static \ae ther finding a large class of possible
viable interior star solutions which present a very rich phenomenology. We
study one illustrative example in more detail.Comment: v1: 5 pages, 1 figure; v2: 6 pages, 1 figure. Matches published
version in EP
The Massive O(N) Non-linear Sigma Model at High Orders
We extend our earlier work on the massive nonlinear sigma model to
other observables. We derive expressions at leading order in the large
expansion at all orders in the loop expansion for the decay constant, vacuum
expectation value, meson-meson scattering and the scalar and vector form
factors. This is done using cactus diagram resummation using a generalized gap
equation and other recursion relations. For general we derive the
expressions for the -th loop order leading logarithms
, up to five-loops for the decay
constant and vacuum expectation value (VEV) and up to four-loops for
meson-meson scattering, the scalar and vector form factors. We also quote our
earlier result for the mass. The large results do not give a good
approximation for the case . We use our results to study the convergence
of the perturbative series and compare with elastic unitarity.Comment: 39 page
Impact of QED corrections to Higgs decay into four leptons at the LHC
At the LHC a precise measurement of the Higgs boson mass (if discovered), at
the level of 0.1-1%, will be possible through the channel g g --> H --> 4l for
a wide range of Higgs mass values. To match such an accuracy, the systematic
effects induced by QED corrections need to be investigated. In the present
study the calculation of O(alpha) and higher order QED corrections is
illustrated as well as their impact on the Higgs mass determination, once
realistic event selection criteria for charged leptons and photons are
considered.Comment: 5 pages, 5 figures, 1 table. Presented at HEP2005 July 21st-27th,
2005, Lisboa, Portugal and at RADCOR 2005, Shonan Village, October 2nd-7th,
2005, Japa
Photon pair production at flavour factories with per mille accuracy
We present a high-precision QED calculation, with 0.1% theoretical accuracy,
of two photon production in annihilation, as required by more and
more accurate luminosity monitoring at flavour factories. The accuracy of the
approach, which is based on the matching of exact next-to-leading order
corrections with a QED Parton Shower algorithm, is demonstrated through a
detailed analysis of the impact of the various sources of radiative corrections
to the experimentally relevant observables. The calculation is implemented in
the latest version of the event generator BabaYaga, available for precision
simulations of photon pair production at colliders of moderately high
energies.Comment: 11 pages, 5 figures, 1 tabl
The 1+1+2 formalism for Scalar-Tensor gravity
We use the 1+1+2 covariant approach to clarify a number of aspects of
spherically symmetric solutions of non-minimally coupled scalar tensor
theories. Particular attention is focused on the extension of Birkhoff's
theorem and the nature of quasi-local horizons in this context.Comment: 27 pages, accepted versio
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