Primordial fluctuations without scalar fields

We revisit the question of whether fluctuations in hydrodynamical, adiabatical matter could explain the observed structures in our Universe. We consider matter with variable equation of state w=p_0/\ep_0 and a concomitant (under the adiabatic assumption) density dependent speed of sound, $c_s$. We find a limited range of possibilities for a set up when modes start inside the Hubble radius, then leaving it and freezing out. For expanding Universes, power-law w(\ep_0) models are ruled out (except when $c_s^2\propto w \ll 1$, requiring post-stretching the seeded fluctuations); but sharper profiles in $c_s$ do solve the horizon problem. Among these, a phase transition in $c_s$ is notable for leading to scale-invariant fluctuations if the initial conditions are thermal. For contracting Universes all power-law w(\ep_0) solve the horizon problem, but only one leads to scale-invariance: w\propto \ep_0^2 and c_s\propto \ep_0. This model bypasses a number of problems with single scalar field cyclic models (for which $w$ is large but constant)

Femtosecond Dynamics of Isolated Phenylcarbenes

International audienceUnderstanding the primary photophysical processes in molecules is essential for interpreting their photochemistry, because molecules rarely react from the initially excited electronic state. In this study the ultrafast excited-state dynamics of chlorophenylcarbene (CPC) and trifluoromethylphenylcarbene (TFPC), two species that are considered as models for carbene dynamics, were investigated by femtosecond time-resolved pump probe spectroscopy in the gas phase. Their dynamics was followed in real time by time-resolved photoionization and photoelectron imaging. CPC was excited at 265 nm into the 3 1A′ state, corresponding to excitation from a π-orbital of the aromatic ring into the LUMO. The LUMO contains a contribution of the p-orbital at the carbene center. Three time constants are apparent in the photoelectron images: A fast decay process with τ1 ≈ 40 fs, a second time constant of τ2 ≈ 350 fs, and an additional time constant of τ3 ≈ 1 ps. The third time constant is only visible in the time-dependence of low kinetic energy electrons. Due to the dense manifold of excited states between 3.9 and 5 eV, known from ab initio calculations, the recorded time-resolved electron images show broad and unstructured bands. A clear population transfer between the states thus can not directly be observed. The fast deactivation process is linked to either a population transfer between the strongly coupled excited states between 3.9 and 5.0 eV or the movement of the produced wave packet out of the Franck−Condon region. Since the third long time constant is only visible for photoelectrons at low kinetic energy, evidence is given that this time constant corresponds to the lifetime of the lowest excited A 1A′ state. The remaining time constant reflects a deactivation of the manifold of states in the range 3.9−5.0 eV down to the A 1A′ state

Shining Light on Modifications of Gravity

Many modifications of gravity introduce new scalar degrees of freedom, and in such theories matter fields typically couple to an effective metric that depends on both the true metric of spacetime and on the scalar field and its derivatives. Scalar field contributions to the effective metric can be classified as conformal and disformal. Disformal terms introduce gradient couplings between scalar fields and the energy momentum tensor of other matter fields, and cannot be constrained by fifth force experiments because the effects of these terms are trivial around static non-relativistic sources. The use of high-precision, low-energy photon experiments to search for conformally coupled scalar fields, called axion-like particles, is well known. In this article we show that these experiments are also constraining for disformal scalar field theories, and are particularly important because of the difficulty of constraining these couplings with other laboratory experiments.Comment: 20 pages, 10 figures. v2: Matches version accepted by JCAP; additional discussion of the strong coupling scale. Conclusions unchange

Quantum corrections to generic branes: DBI, NLSM, and more

We study quantum corrections to hypersurfaces of dimension $d+1>2$ embedded in generic higher-dimensional spacetimes. Manifest covariance is maintained throughout the analysis and our methods are valid for arbitrary co-dimension and arbitrary bulk metric. A variety of theories which are prominent in the modern amplitude literature arise as special limits: the scalar sector of Dirac-Born-Infeld theories and their multi-field variants, as well as generic non-linear sigma models and extensions thereof. Our explicit one-loop results unite the leading corrections of all such models under a single umbrella. In contrast to naive computations which generate effective actions that appear to violate the non-linear symmetries of their classical counterparts, our efficient methods maintain manifest covariance at all stages and make the symmetry properties of the quantum action clear. We provide an explicit comparison between our compact construction and other approaches and demonstrate the ultimate physical equivalence between the superficially different results

Delayed bowel perforation following suprapubic catheter insertion

BACKGROUND: Complications of suprapubic catheter insertion are rare but can be significant. We describe an unusual complication of a delayed bowel perforation following suprapubic catheter insertion. CASE PRESENTATION: A gentleman presented with features of peritonitis and feculent discharge along a suprapubic catheter two months after insertion of the catheter. CONCLUSION: Bowel perforation is the most feared complication of suprapubic catheter insertion especially in patients with lower abdominal scar. The risk may be reduced with the use of ultrasound scan guidance

Positivity bounds on dark energy: when matter matters

Positivity bounds — constraints on any low-energy effective field theory imposed by the fundamental axioms of unitarity, causality and locality in the UV — have recently been used to constrain scalar-tensor theories of dark energy. However, the coupling to matter fields has so far played a limited role. We show that demanding positivity when including interactions with standard matter fields leads to further constraints on the dark energy parameter space. We demonstrate how implementing these bounds as theoretical priors affects cosmological parameter constraints and explicitly illustrate the impact on a specific Effective Field Theory for dark energy. We also show in this model that the existence of a standard UV completion requires that gravitational waves must travel superluminally on cosmological backgrounds

t-3-Benzyl-r-2,c-6-bis­(4-methoxy­phen­yl)­piperidin-4-one

In the title compound, C26H27NO3, the piperidine ring adopts a chair conformation. The two methoxy­phenyl groups attached to the piperidine ring at positions 2 and 6 have equatorial orientations and make a dihedral angle of 87.33 (8)°. The benzyl group at position 3 has an equatorial orientation. The phenyl ring of the benzyl group makes dihedral angles of 75.60 (9) and 73.69 (9)° with the two benzene rings. Mol­ecules are linked by inter­molecular N—H⋯O and C—H⋯O hydrogen bonds and by C—H⋯π inter­actions