When Matter Matters

We study a recently proposed scenario for the early universe: Subluminal Galilean Genesis. We prove that without any other matter present in the spatially flat Friedmann universe, the perturbations of the Galileon scalar field propagate with a speed at most equal to the speed of light. This proof applies to all cosmological solutions -- to the whole phase space. However, in a more realistic situation, when one includes any matter which is not directly coupled to the Galileon, there always exists a region of phase space where these perturbations propagate superluminally, indeed with arbitrarily high speed. We illustrate our analytic proof with numerical computations. We discuss the implications of this result for the possible UV completion of the model.Comment: 16 pages, 3 figures. v2 reflects version accepted for publication in JCAP. Changes include a reorganisation of section order, a new figure 1 and additional reference

Dust of Dark Energy

We introduce a novel class of field theories where energy always flows along timelike geodesics, mimicking in that respect dust, yet which possess non-zero pressure. This theory comprises two scalar fields, one of which is a Lagrange multiplier enforcing a constraint between the other's field value and derivative. We show that this system possesses no wave-like modes but retains a single dynamical degree of freedom. Thus, the sound speed is always identically zero on all backgrounds. In particular, cosmological perturbations reproduce the standard behaviour for hydrodynamics with vanishing sound speed. Using all these properties we propose a model unifying Dark Matter and Dark Energy in a single degree of freedom. In a certain limit this model exactly reproduces the evolution history of Lambda-CDM, while deviations away from the standard expansion history produce a potentially measurable difference in the evolution of structure.Comment: 13 pages, 3 figures. Added references, corrected language

Covariant Galileon

We consider the recently introduced "galileon" field in a dynamical spacetime. When the galileon is assumed to be minimally coupled to the metric, we underline that both field equations of the galileon and the metric involve up to third-order derivatives. We show that a unique nonminimal coupling of the galileon to curvature eliminates all higher derivatives in all field equations, hence yielding second-order equations, without any extra propagating degree of freedom. The resulting theory breaks the generalized "Galilean" invariance of the original model.Comment: 10 pages, no figure, RevTeX4 format; v2 adds footnote 1, Ref. [12], reformats the link in Ref. [14], and corrects very minor typo

G-Bounce

We present a wide class of models which realise a bounce in a spatially flat Friedmann universe in standard General Relativity. The key ingredient of the theories we consider is a noncanonical, minimally coupled scalar field belonging to the class of theories with Kinetic Gravity Braiding / Galileon-like self-couplings. In these models, the universe smoothly evolves from contraction to expansion, suffering neither from ghosts nor gradient instabilities around the turning point. The end-point of the evolution can be a standard radiation-domination era or an inflationary phase. We formulate necessary restrictions for Lagrangians needed to obtain a healthy bounce and illustrate our results with phase portraits for simple systems including the recently proposed Galilean Genesis scenario.Comment: 28 pages. v2 reflects version accepted for publication in JCAP. References and minor comments adde

Enhancing the tensor-to-scalar ratio in simple inflation

We show that in theories with a nontrivial kinetic term the contribution of the gravitational waves to the CMB fluctuations can be substantially larger than that is naively expected in simple inflationary models. This increase of the tensor-to-scalar perturbation ratio leads to a larger B-component of the CMB polarization, thus making the prospects for future detection much more promising. The other important consequence of the considered model is a higher energy scale of inflation and hence higher reheating temperature compared to a simple inflation.Comment: 9 pages, 1 figure and references are added, discussion is slightly extended, published versio

Comment on superluminality in general relativity

General relativity provides an appropriate framework for addressing the issue of sub- or superluminality as an apparent effect. Even though a massless particle travels on the light cone, its average velocity over a finite path measured by different observers is not necessarily equal to the velocity of light, as a consequence of the time dilation or contraction in gravitational fields. This phenomenon occurs in either direction (increase or depletion) irrespectively of the details and strength of the gravitational interaction. Hence, it does not intrinsically guarantee superluminality, even when the gravitational field is reinforced.Comment: 6 page

Suppressing Quantum Fluctuations in Classicalization

We study vacuum quantum fluctuations of simple Nambu-Goldstone bosons - derivatively coupled single scalar-field theories possessing shift-symmetry in field space. We argue that quantum fluctuations of the interacting field can be drastically suppressed with respect to the free-field case. Moreover, the power-spectrum of these fluctuations can soften to become red for sufficiently small scales. In quasiclassical approximation, we demonstrate that this suppression can only occur for those theories that admit such classical static backgrounds around which small perturbations propagate faster than light. Thus, a quasiclassical softening of quantum fluctuations is only possible for theories which classicalize instead of having a usual Lorentz invariant and local Wilsonian UV- completion. We illustrate our analysis by estimating the quantum fluctuations for the DBI-like theories.Comment: 6 pages, no figures, published version, more general discussion of uncertainty relation in QFT, improved and more general derivation of the main resul

Simple generalizations of Anti-de Sitter space-time

We consider new cosmological solutions which generalize the cosmological patch of the Anti-de Sitter (AdS) space-time, allowing for fluids with equations of state such that $w\neq -1$. We use them to derive the associated full manifolds. We find that these solutions can all be embedded in flat five-dimensional space-time with $--+++$ signature, revealing deformed hyperboloids. The topology and causal-structure of these spaces is therefore unchanged, and closed time-like curves are identified, before a covering space is considered. However the structure of Killing vector fields is entirely different and so we may expect a different structure of Killing horizons in these solutions.Comment: 6 Pages, 5 Figures, Corrections and additions made for publication in Journal of Classical and Quantum Gravit

Utilisation of co-streams in the Norwegian food processing industry

Food losses occur throughout the entire food chain, from primary production via postharvest handling and storage, to food processing, distribution, retailing and consumption. Globally, food losses account for about one third of the total food produced for human consumption. The aim of this report was to map the production and utilisation of co-streams in the food processing industry in Norway and to discuss possibilities for alternative utilisation based on qualitative aspects of the co-streams, and current legislation. This report is produced by work package 3 in the CYCLE project (2013-2016), “Total utilisation of raw materials in the supply chain for food with a bio-economical perspective”. The CYCLE project aims to improve resource utilisation in the Norwegian food chain by developing sustainable eco-friendly bio-processes and novel technology, in close relationship with food industry partners. Inputs and outputs of organic materials were roughly mapped at selected food processing plants presenting three Norwegian food chains: 1) Vegetables and potatoes; 2) white and pelagic fish; and 3) poultry. Data was collected during plant visits in June 2013, and later checked by staff from the described plants. The report describes the qualitative properties of co-streams, and their current utilisation as feed, fertiliser and as substrate for bioenergy production. We also present relevant regulations in EU and Norway regarding processing and utilisation of co-streams, and discuss alternative utilisation. Altogether, the food processing plants had significant market shares in Norway within fresh potatoes (38%), lettuce (17%), poultry meat (24%) and white and pelagic fish, where export makes up a large proportion. Generally, a large proportion of the raw materials were utilised as food and feed. On average for all plants, 75% of the raw material was utilised in food products, 21% in feed products, 1% in fertiliser and bioenergy production and 3% was deposited in landfill. The plants used in average 8.6 tonnes of process water per tonne of food produced, but the amount varied considerably between the plants. Possible improvements in the utilisation of raw materials and co-streams include a higher degree of utilisation in food products, and developing new or improved feed components from co-streams with increased nutritional value. Due to the current high degree of utilisation in food and feed applications with high economic values, the potential for bioenergy and fertiliser production is limited to certain risk materials. Feed potatoes and vegetables and feathers, bones, blood, viscera and skin from fish or poultry have considerable potential for better utilisation for food or feed. Relevant processing methods for these co-streams are fractionation, hydrolysis, fermentation and drying