Extranatural Inflation Redux

The success of a given inflationary model crucially depends upon two features: its predictions for observables such as those of the Cosmic Microwave background (CMB) and its insensitivity to the unknown ultraviolet (UV) physics such as quantum gravitational effects. Extranatural inflation is a well motivated scenario which is insensitive to UV physics by construction. In this five dimensional model, the fifth dimension is compactified on a circle and the zero mode of the fifth component of a bulk $U(1)$ gauge field acts as the inflaton. In this work, we study simple variations of the minimal extranatural inflation model in order to improve its CMB predictions while retaining its numerous merits. We find that it is possible to obtain CMB predictions identical to those of e.g. ${\cal R} + {\cal R}^2$ Starobinsky model of inflation and show that this can be done in the most minimal way by having two additional extra light fermionic species in the bulk, with the same $U(1)$ charges. We then find the constraints that CMB observations impose on the parameters of the model.Comment: Journal version (to appear in Phy. Rev. D

Self-interactions of ULDM to the rescue?

One of the most important questions in cosmology is concerning the fundamental nature of dark matter (DM). DM could consist of spinless particles of very small mass i.e. $m \sim 10^{-22}\ \text{eV}$. This kind of ultralight dark matter (ULDM) would form cored density profiles (called "solitons") at the centre of galaxies. In this context, recently it has been argued that (a) there exists a power law relation between the mass of the soliton and mass of the surrounding halo called the Soliton-Halo (SH) relation, and, (b) the requirement of satisfying observed galactic rotation curves as well as SH relations is so stringent that ULDM is disfavoured from comprising $100\%$ of the total cosmological dark matter. In this work, we revisit these constraints for ULDM particles with non-negligible quartic self-interactions. Using a recently obtained soliton-halo relation which takes into account the effect of self-interactions, we present evidence which suggests that, for $m = 10^{-22}\ \text{eV}$, the requirement of satisfying both galactic rotation curves as well as SH relations can be fulfilled with repulsive self-coupling$\lambda \sim \mathcal{O}(10^{-90})$.Comment: 26 pages, 8 figure

Design, Management and Key Success Factors of an Offshore Cathodic Protection System for Corrosion Control

Corrosion is a very prevalent issue for offshore operations in the oil and gas industry. If the corrosion issues are not addressed adequately, these may lead to quality failures, safety incidents, compromise to asset integrity and high inspection costs. This research paper discusses and analyzes corrosion types, corrosion threats, mechanisms to protect against corrosion, design and management of cathodic protection system, and key success factors for a cathodic protection system for an offshore oil and gas production system

ULDM self-interactions, tidal effects and tunnelling out of satellite galaxies

It is well-known that Dark Matter (DM) inside a satellite galaxy orbiting a host halo experiences a tidal potential. For Ultra-Light Dark Matter (ULDM), due to its wave-like nature, one expects it to tunnel out of the satellite - if this happens sufficiently quickly, then the satellite will not survive over cosmological timescales, severely constraining the dark matter model. In this paper, we study the effects of the inevitable quartic self-interaction of scalar ULDM on the lifetimes of satellite galaxies by looking for quasi-stationary solutions with outgoing wave boundary conditions. For a satellite with some known core mass and orbital period, we find that, attractive (repulsive) self-interactions decrease (increase) the rate of tunnelling of DM out of it. In particular, for satellite galaxies with core mass $\sim \mathcal{O}(10^7-10^8)\ M_\odot$ and orbital period $\sim \mathcal{O}(1)\ \text{Gyr}$, one can impose constraints on the strength of self-interactions as small as $\lambda\sim \mathcal{O}(10^{-92})$. For instance, for ULDM mass $m = 10^{-22}\ \text{eV}$, the existence of the Fornax dwarf galaxy necessitates attractive self-interactions with $\lambda \lesssim -2.12 \times 10^{-91}$.Comment: 27 pages, 13 figure