2,055,628 research outputs found
Modified Einstein and Finsler Like Theories on Tangent Lorentz Bundles
We study modifications of general relativity, GR, with nonlinear dispersion
relations which can be geometrized on tangent Lorentz bundles. Such modified
gravity theories, MGTs, can be modeled by gravitational Lagrange density
functionals with generalized/ modified scalar
curvature , trace of matter field tensors and modified
Finsler like generating function . In particular, there are defined
extensions of GR with extra dimensional "velocity/ momentum" coordinates. For
four dimensional models, we prove that it is possible to decouple and integrate
in very general forms the gravitational fields for
-modified gravity using nonholonomic 2+2 splitting
and nonholonomic Finsler like variables . We study the modified motion and
Newtonian limits of massive test particles on nonlinear geodesics approximated
with effective extra forces orthogonal to the four--velocity. We compute the
constraints on the magnitude of extra-accelerations and analyze perihelion
effects and possible cosmological implications of such theories. We also derive
the extended Raychaudhuri equation in the framework of a tangent Lorentz
bundle. Finally, we speculate on effective modelling of modified theories by
generic off-diagonal configurations in Einstein and/or MGTs and Finsler
gravity. We provide some examples for modified stationary (black) ellipsoid
configurations and locally anisotropic solitonic backgrounds.Comment: latex2e, 20 pages; version accepted to IJMPD; changed title and
modifications following requests of refere
Testing gravity with non-Gaussianity
We show that modified gravity presents distinctive nonlinear features on the
Cosmic Microwave Background (CMB) anisotropies comparing with General
Relativity (GR). We calculate the contribution to the CMB non-Gaussianity from
nonlinear Sachs-Wolfe effect in gravity and show that, contrary to GR's
contribution which is typically , the contribution in
gravity is sensitive to the nonlinear structure of and can be
large in principle. Optimistically, this gives an alternative origin for the
possibly observed large CMB non-Gaussianities besides the primordial ones. On
the other hand, such nonlinear features can be employed to provide a new
cosmological test of or other modified theories of gravitation, which is
unique and independent of previously known tests.Comment: 4 pages, 1 figure, v2 to match the published versio
Constraining Modified Gravity with Euclid
Future proposed satellite missions as Euclid can offer the opportunity to
test general relativity on cosmic scales through mapping of the galaxy weak
lensing signal. In this paper we forecast the ability of these experiments to
constrain modified gravity scenarios as those predicted by scalar-tensor and
theories. We found that Euclid will improve constraints expected from
the PLANCK satellite on these modified gravity models by two orders of
magnitude. We discuss parameter degeneracies and the possible biases introduced
by modified gravity
Inference in Regression Models with Many Regressors
We investigate the behavior of various standard and modified F, LR and LM tests in linear homoskedastic regressions, adapting an alternative asymptotic framework where the number of regressors and possibly restrictions grows proportionately to the sample size. When restrictions are not numerous, the rescaled classical test statistics are asymptotically chi-squared irrespective of whether there are many or few regressors. However, when restrictions are numerous, standard asymptotic versions of classical tests are invalid. We propose and analyze asymptotically valid versions of the classical tests, including those that are robust to the numerosity of regressors and restrictions. The local power of all asymptotically valid tests under consideration turns out to be equal. The "exact" F test that appeals to critical values of the F distribution is also asymptotically valid and robust to the numerosity of regressors and restrictions.Alternative asymptotic theory, linear regression, test size, test power, F test, Wald test, Likelihood Ratio test, Lagrange Multiplier test
Modified f(G) gravity models with curvature-matter coupling
A modified f(G) gravity model with coupling between matter and geometry is
proposed, which is described by the product of the Lagrange density of the
matter and an arbitrary function of the Gauss-Bonnet term. The field equations
and the equations of motion corresponding to this model show the
non-conservation of the energy-momentum tensor, the presence of an extra-force
acting on test particles and the non-geodesic motion. Moreover, the energy
conditions and the stability criterion at de Sitter point in the modified f(G)
gravity models with curvature-matter coupling are derived, which can degenerate
to the well-known energy conditions in general relativity. Furthermore, in
order to get some insight on the meaning of these energy conditions, we apply
them to the specific models of f(G) gravity and the corresponding constraints
on the models are given. In addition, the conditions and the candidate for
late-time cosmic accelerated expansion in the modified f(G) gravity are studied
by means of conditions of power-law expansion and the equation of state of
matter less than -1/ 3 .Comment: 13 pages, 4 figure
Non-analytical power law correction to the Einstein-Hilbert action: gravitational wave propagation
We analyze the features of the Minkowskian limit of a particular
non-analytical f(R) model, whose Taylor expansion in the weak field limit does
not hold, as far as gravitational waves (GWs) are concerned. We solve the
corresponding Einstein equations and we find an explicit expression of the
modified GWs as the sum of two terms, i.e. the standard one and a modified
part. As a result, GWs in this model are not transverse, and their polarization
is different from that of General Relativity. The velocity of the GW modified
part depends crucially on the parameters characterizing the model, and it
mostly results much smaller than the speed of light. Moreover, this
investigation allows one to further test the viability of this particular f(R)
gravity theory as far as interferometric observations of GWs are concerned.Comment: 18 pages, 3 figure
Using approximate roots for irreducibility and equi-singularity issues in K[[x]][y]
We provide an irreducibility test in the ring K[[x]][y] whose complexity is
quasi-linear with respect to the valuation of the discriminant, assuming the
input polynomial F square-free and K a perfect field of characteristic zero or
greater than deg(F). The algorithm uses the theory of approximate roots and may
be seen as a generalization of Abhyankhar's irreducibility criterion to the
case of non algebraically closed residue fields. More generally, we show that
we can test within the same complexity if a polynomial is pseudo-irreducible, a
larger class of polynomials containing irreducible ones. If is
pseudo-irreducible, the algorithm computes also the valuation of the
discriminant and the equisingularity types of the germs of plane curve defined
by F along the fiber x=0.Comment: 51 pages. Title modified. Slight modifications in Definition 5 and
Proposition 1
Asphalt Mixture with Scrap Tire Rubber and Nylon Fiber from Waste Tires: Laboratory Performance and Preliminary M‐E Design Analysis
Scrap tire rubber and nylon fiber are waste materials that could potentially be recycled and used to improve the mechanical properties of asphalt pavement. The objective of this research was to investigate the properties of scrap tire rubber and nylon fiber (R‐F) modified warm mix asphalt mixture (WMA). The high‐temperature performance was estimated by the Hamburg wheel-tracking testing (HWTT) device. The low‐temperature cracking performance was evaluated by the disk‐shaped compact tension (DCT) test and the indirect tensile strength (IDT) test. The stress and strain relationship was assessed by the dynamic modulus test at various temperatures and frequencies. The extracted asphalt binder was evaluated by the dynamic shear rheometer (DSR). Pavement distresses were predicted by pavement mechanistic‐empirical (M‐E) analysis. The test results showed that: (1) The R‐F modified WMA had better high‐temperature rutting performance. The dynamic modulus of conventional hot mix asphalt mixture (HMA) was 21.8% ~ 103% lower than R‐ F modified WMA at high temperatures. The wheel passes and stripping point of R‐F modified WMA were 2.17 and 5.8 times higher than those of conventional HMA, respectively. Moreover, the R‐F modified warm mix asphalt had a higher rutting index than the original asphalt. (2) R‐F modified WMA had better cracking resistance at a low temperature. The failure energy of the R‐F modified WMA was 24.3% higher than the conventional HMA, and the fracture energy of the R‐F modified WMA was 7.7% higher than the conventional HMA. (3) The pavement distress prediction results showed the same trend compared with the laboratory testing performance in that the R‐F modified WMA helped to improve the IRI, AC cracking, and rutting performance compared with the conventional HMA. In summary, R‐F modified WMA can be applied in pavement construction
Implications of the Holst term in a theory with torsion
We analyze a modified theory of gravity in the Palatini formulation,
when an Holst term endowed with a dynamical Immirzi field is included. We study
the basic features of the model, especially in view of liminating the torsion
field via the Immirzi field and the scalar-tensor degrees of freedom of the
model. The main task of this study is the investigation of the
morphology of the gravitational wave polarization when their coupling to a
circle of test particles is considered. We first observe that the dynamics of
the scalar mode of the Lagrangian is frozen out, since its first order
term identically vanishes. This allows a detailed characterization of the
linearized theory, which outlines the emergence of a modified Newtonian
potential in the static limit, and when time independence is relaxed a standard
gravitational wave plus the scalar wave associated to the Immirzi field.
Investigating the effect of the coupling of this scalar-tensor wave on a circle
of test particles, we arrive to define two effective gravitational
polarizations, corresponding to an equivalent phenomenological wave, whose
morphology is anomalous with respect the standard case of General Relativity.
In fact, the particle circle suffers modifications as it was subjected to
modified plus and cross modes, whose specific features depend on the model free
parameters and are, in principle, detectable via a data analysis procedure.Comment: 8 pages, 4 figures, accepted for publication in Physical Review
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