Ph. Brax

Conceptual design of the International Axion Observatory (IAXO)

The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO will look for axions or axion-like particles (ALPs) originating in the Sun via the Primakoff conversion of the solar plasma photons. In terms of signal-to-noise ratio, IAXO will be about 4–5 orders of magnitude more sensitive than CAST, currently the most powerful axion helioscope, reaching sensitivity to axion-photon couplings down to a few × 10−12 GeV−1 and thus probing a large fraction of the currently unexplored axion and ALP parameter space. IAXO will also be sensitive to solar axions produced by mechanisms mediated by the axion-electron coupling gae with sensitivity — for the first time — to values of gae not previously excluded by astrophysics. With several other possible physics cases, IAXO has the potential to serve as a multi-purpose facility for generic axion and ALP research in the next decade. In this paper we present the conceptual design of IAXO, which follows the layout of an enhanced axion helioscope, based on a purpose-built 20 m-long 8-coils toroidal superconducting magnet. All the eight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able to focus the signal photons into ~ 0.2 cm2 spots that are imaged by ultra-low-background Micromegas x-ray detectors. The magnet is built into a structure with elevation and azimuth drives that will allow for solar tracking for ~ 12 h each day.

Is the radion a chameleon

The chameleon mechanism is a way to give an effective mass to a light scalar field via field self-interaction and interaction with matter. We study this mechanism in models in which the couplings are field dependent and find that the properties are very different from the case of constant couplings. The consequences of a runaway potential for the radion field in brane world scenarios and whether the radion can play the role of dark energy is investigated. The cosmological evolution during the inflationary epoch, the radiation and the matter dominated epochs are discussed as is the compatibility of the radion field with local tests of gravity.

Tachyon kinks on non-BPS D-branes

We consider solitonic solutions of the DBI tachyon effective action for a non-BPS brane. When wrapped on a circle, these solutions are regular and have a finite energy. We show that in the decompactified limit, these solitons give Sens infinitely thin finite energy kink -- interpreted as a BPS brane -- provided that some conditions on the potential hold. In particular, if for large

Chameleon Dark Energy

T

Gauge coupling variation in brane models

the potential is exponential,

Tuning the Mass of Chameleon Fields in Casimir Force Experiments

V = e^{-T^a}

Small scale structure formation in chameleon cosmology

, then Sens solution is only found for

Spherical collapse in chameleon models

a<1

Open supermembranes coupled to M-theory five-branes

. For power-law potentials

Neutron interferometry constrains dark energy chameleon fields

V = 1/T^b