E. I. Guendelman

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.

Dynamical measure and field theory models free of the cosmological constant problem

Summary of abstract Field theory models including gauge theories with SSB are presented where the energy density of the true vacuum state (TVS) is zero without fine tuning. The above models are constructed in the gravitational theory where a measure of integration \Phi in the action is not necessarily \sqrt{-g} but it is determined dynamically through additional degrees of freedom. The ratio \Phi/\sqrt{-g} is a scalar field which can be solved in terms of the matter degrees of freedom due to the existence of a constraint. We study a few explicit field theory models where it is possible to combine the solution of the cosmological constant problem with: 1) possibility for inflationary scenario for the early universe; 2) spontaneously broken gauge unified theories (including fermions). The models are free from the well known problem of the usual scalar-tensor theories in what is concerned with the classical GR tests. The only difference of the field equations in the Einstein frame from the canonical equations of the selfconsistent system of Einsteins gravity and matter fields, is the appearance of the effective scalar field potential which vanishes in TVS without fine tuning.

Inflation and transition to a slowly accelerating phase from SSB of scale invariance

We consider the effects of adding a scale-invariant R2 term to the action of the scale-invariant model (SIM) studied previously by one of us (Guendelman E I 1999 Mod. Phys. Lett. A 14 1043). The SIM belongs to the general class of theories, where an integration measure independent of the metric is introduced. To implement scale invariance (SI), a dilaton field is introduced. The integration of the equations of motion associated with the new measure gives rise to the spontaneous symmetry breaking (SSB) of SI. After SSB of SI in the model with the R2 term, it is found that a non-trivial potential for the dilaton is generated. This potential contains two flat regions: one associated with the Planck scale and with an inflationary phase, while the other flat region is associated with a very small vacuum energy (VE) and is associated with the present slowly accelerated phase of the universe (SAPH). The smallness of the VE in the SAPH is understood through the see-saw mechanism introduced in SIM.We consider the effects of adding a scale invariant

Principle of nongravitating vacuum energy and some of its consequences.

R^{2}

String and brane models with spontaneously or dynamically induced tension

term to the action of the scale invariant model (SIM) studied previously by one of us (E.I.G., Mod. Phys. Lett. A14, 1043 (1999)). The SIM belongs to the general class of theories, where an integration measure independent of the metric is introduced. To implement scale invariance (S.I.), a dilaton field is introduced. The integration of the equations of motion associated with the new measure gives rise to the spontaneous symmetry breaking (S.S.B) of S.I.. After S.S.B. of S.I. in the model with the

Strings and branes with a modified measure

R^{2}

Emergent Cosmology, Inflation and Dark Energy

term, it is found that a non trivial potential for the dilaton is generated. This potential contains two flat regions: one associated with the Planck scale and with an inflationary phase, while the other flat region is associated to a very small vacuum energy (V.E.) and is associated to the present slowly accelerated phase of the universe (S.A.PH). The smallness of the V.E. in the S.A.PH. is understood through the see saw mechanism introduced in S.I.M.

Gravitational Theory Without the Cosmological Constant Problem

For Einsteins General Relativity (GR) or the alternatives suggested up to date

A two measure model of dark energy and dark matter

the vacuum energy gravitates. We present a model where a new measure is introduced for integration of the total action in the D-dimensional space-time. This measure is built from D scalar fields

Scale Symmetry Breaking From Total Derivative Densities and the Cosmological Constant Problem

\varphi_{a}