Marine tethysuchian crocodyliform from the ?Aptian-Albian (Lower Cretaceous) of the Isle of Wight, UK

A marine tethysuchian crocodyliform from the Isle of Wight, most likely from the Upper Greensand Formation (upper Albian, Lower Cretaceous), is described. However, we cannot preclude it being from the Ferruginous Sands Formation (upper Aptian), or more remotely, the Sandrock Formation (upper Aptian-upper Albian). The specimen consists of the anterior region of the right dentary, from the tip of the dentary to the incomplete fourth alveolus. This specimen increases the known geological range of marine tethysuchians back into the late Lower Cretaceous. Although we refer it to Tethysuchia incertae sedis, there are seven anterior dentary characteristics that suggest a possible relationship with the Maastrichtian-Eocene clade Dyrosauridae. We also review ‘middle’ Cretaceous marine tethysuchians, including putative Cenomanian dyrosaurids. We conclude that there is insufficient evidence to be certain that any known Cenomanian specimen can be safely referred to Dyrosauridae, as there are some cranial similarities between basal dyrosaurids and Cenomanian–Turonian marine ‘pholidosaurids’. Future study of middle Cretaceous tethysuchians could help unlock the origins of Dyrosauridae and improve our understanding of tethysuchian macroevolutionary trends

The dynamics of the gravitational two-body problem at fourth post-Newtonian order and at quadratic order in the Newton constant

We derive the conservative part of the Lagrangian and the energy of a gravitationally bound two-body system at fourth post-Newtonian order, up to terms quadratic in the Newton constant. We also show that such terms are compatible with Lorentz invariance and we write an ansatz for the center-of-mass position. The remaining terms carrying higher powers of the Newton constant are currently under investigation.Comment: 24 pages, 2 figures. Typos in formulae corrected, references added, more comments in the conclusion in v

Bouncing pre-big bang on the brane

A regular bouncing universe is obtained in the context of a dilaton-gravity brane world scenario. The scale factor starts in a contracting inflationary phase both in the Einstein and in the string frame, it then undergoes a bounce (due to interaction with the bulk Weyl tensor), and subsequently enters into a decelerated expanding era. This graceful exit is obtained at low curvature and low coupling, and without violating the Null Energy Condition.Comment: 16 pages, 3 figures; final version to be published on PRD. General improvement of section II (better specification of the matter content on the brane and discussion about the late time behavior), main results unchanged; 2 references adde

Probing the Planck Scale with Neutrino Oscillations

Quantum gravity "foam", among its various generic Lorentz non-invariant effects, would cause neutrino mixing. It is shown here that, if the foam is manifested as a nonrenormalizable effect at scale M, the oscillation length generically decreases with energy $E$ as (E/M)^(-2). Neutrino observatories and long-baseline experiments should have therefore already observed foam-induced oscillations, even if M is as high as the Planck energy scale. The null results, which can be further strengthened by better analysis of current data and future experiments, can be taken as experimental evidence that Lorentz invariance is fully preserved at the Planck scale, as is the case in critical string theory.Comment: 11 pages, 2 figures. Final version published in PRD. 1 figure, references, clarifications and explanations added. Results unchange

A Solution to the Graceful Exit Problem in Pre-Big Bang Cosmology

We examine the string cosmology equations with a dilaton potential in the context of the Pre-Big Bang Scenario with the desired scale factor duality, and give a generic algorithm for obtaining solutions with appropriate evolutionary properties. This enables us to find pre-big bang type solutions with suitable dilaton behaviour that are regular at $t=0$, thereby solving the graceful exit problem. However to avoid fine tuning of initial data, an `exotic' equation of state is needed that relates the fluid properties to the dilaton field. We discuss why such an equation of state should be required for reliable dilaton behaviour at late times.Comment: 16 pages LaTeX, 5 figures. To appear in Physical Review

Causal Entropy Bound for Non-Singular Cosmologies

The conditions for validity of the Causal Entropy Bound (CEB) are verified in the context of non-singular cosmologies with classical sources. It is shown that they are the same conditions that were previously found to guarantee validity of the CEB: the energy density of each dynamical component of the cosmic fluid needs to be sub-Planckian and not too negative, and its equation of state needs to be causal. In the examples we consider, the CEB is able to discriminate cosmologies which suffer from potential physical problems more reliably than the energy conditions appearing in singularity theorems.Comment: 16 pages, no figures, acknowledgments adde

Inflation and initial conditions in the pre-big bang scenario

The pre-big bang scenario describes the evolution of the Universe from an initial state approaching the flat, cold, empty, string perturbative vacuum. The choice of such an initial state is suggested by the present state of our Universe if we accept that the cosmological evolution is (at least partially) duality-symmetric. Recently, the initial conditions of the pre-big bang scenario have been criticized as they introduce large dimensionless parameters allowing the Universe to be "exponentially large from the very beginning". We agree that a set of initial parameters (such as the initial homogeneity scale, the initial entropy) larger than those determined by the initial horizon scale, H^{-1}, would be somewhat unnatural to start with. However, in the pre-big bang scenario, the initial parameters are all bounded by the size of the initial horizon. The basic question thus becomes: is a maximal homogeneity scale of order H^{-1} necessarily unnatural if the initial curvature is small and, consequently, H^{-1} is very large in Planck (or string) units? In the impossibility of experimental information one could exclude "a priori", for large horizons, the maximal homogeneity scale H^{-1} as a natural initial condition. In the pre-big bang scenario, however, pre-Planckian initial conditions are not necessarily washed out by inflation and are accessible (in principle) to observational tests, so that their naturalness could be also analyzed with a Bayesan approach, in terms of "a posteriori" probabilities.Comment: 4 pages, Latex, one figure. Many references added. The text has been improved in many points. To appear in Phys. Rev.

Nature of singularities in anisotropic string cosmology

We study nature of singularities in anisotropic string-inspired cosmological models in the presence of a Gauss-Bonnet term. We analyze two string gravity models-- dilaton-driven and modulus-driven cases-- in the Bianchi type-I background without an axion field. In both scenarios singularities can be classified in two ways- the determinant singularity where the main determinant of the system vanishes and the ordinary singularity where at least one of the anisotropic expansion rates of the Universe diverges. In the dilaton case, either of these singularities inevitably appears during the evolution of the system. In the modulus case, nonsingular cosmological solutions exist both in asymptotic past and future with determinant $D=+\infty$ and D=2, respectively. In both scenarios nonsingular trajectories in either future or past typically meet the determinant singularity in past/future when the solutions are singular, apart from the exceptional case where the sign of the time-derivative of dilaton is negative. This implies that the determinant singularity may play a crucial role to lead to singular solutions in an anisotropic background.Comment: 21 pages, 8 figure

Revision of the Late Jurassic teleosaurid genus Machimosaurus (Crocodylomorpha, Thalattosuchia)

© 2014 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. The attached file is the published version of the article