18165833
Generation of large scale magnetic fields in single-field inflation
We consider the generation of large scale magnetic fields in slow-roll inflation. The inflaton field is described in a supergravity framework where the conformal invariance of the electromagnetic field is generically and naturally broken. For each class of inflationary scenarios, we determine the functional dependence of the gauge coupling that is consistent with the observations on the magnetic field strength at various astrophysical scales and, at the same time, avoid a back-reaction problem. Then, we study whether the required coupling functions can naturally emerge in well motivated, possibly string inspired, models. We argue that this is non-trivial and can be realized only for a restricted class of scenarios. This includes power-law inflation where the inflaton field is interpreted as a modulus. However, this scenario seems to be consistent only if the energy scale of inflation is low and the reheating stage prolonged. Another reasonable possibility appears to be small field models since no back-reaction problem is present in this case but, unfortunately, the corresponding scenario cannot be justified in a stringy framework. Finally, large field models do not lead to sensible model building.
118612073
Generation of gravitational waves during early structure formation between cosmic inflation and reheating
In the pre-reheating era, following cosmic inflation and preceding radiation domination, the energy density may be dominated by an oscillating massive scalar condensate, such as is the case for V = m22/2 chaotic inflation. We have found in a previous paper that during this period, a wide range of sub-Hubble scale perturbations are subject to a preheating instability, leading to the growth of density perturbations ultimately collapsing to form non-linear structures. We compute here the gravitational wave signal due to these structures in the linear limit and present estimates for emission in the non-linear limit due to various effects: the collapse of halos, the tidal interactions, the evaporation during the conversion of the inflaton condensate into radiation and finally the ensuing turbulent cascades. The gravitational wave signal could be rather large and potentially testable by future detectors.
31268700
Quintessence with two energy scales
We study quintessence models using low energy supergravity inspired from string theory. We consider effective supergravity with two scales m_S, the string scale, and m_PL, the Planck scale and show that quintessence naturally arises from a supersymmetry breaking hidden sector. As long as supersymmetry is broken by the $F$-term of a Polonyi-like field coupled to the quintessence field in the K\"ahler potential we find that the Ratra-Peebles potential and its supergravity version are generic predictions. This requires that the string scale decouples from the Planck scale, m_S << m_PL. In the context of supergravity, the potential possesses a minimum induced by the supergravity corrections to the Ratra-Peebles potential at low redshifts. We study the physical consequences of the presence of this minimum.
119240885
Constraints on moduli cosmology from the production of dark matter and baryon isocurvature fluctuations
We set constraints on moduli cosmology from the production of dark matter—radiation and baryon— radiation isocurvature fluctuations through modulus decay, assuming the modulus remains light during inflation. We find that the moduli problem becomes worse at the perturbative level as a significant part of the parameter space m σ (modulus mass)—σ inf (modulus vacuum expectation value at the end of inflation) is constrained by the nonobservation of significant isocurvature fluctuations. We discuss in detail the evolution of the modulus vacuum expectation value and perturbations, in particular, the consequences of Hubble scale corrections to the modulus potential, and the stochastic motion of the modulus during inflation. We show, in particular, that a high modulus mass scale m σ ≳ 100 TeV, which allows the modulus to evade big bang nucleosynthesis constraints is strongly constrained at the perturbative level. We find that generically, solving the moduli problem requires the inflationary scale to be much smaller than 10 13 GeV.
15021448
Amplitude of superhorizon cosmological perturbations
We study the influence of reheating on super-horizon density perturbations and gravitational waves. We correct wrong claims [L. P. Grishchuk Phys. Rev. D 50, 7154 (1994) and gr-qc/9801011] about the joining of perturbations at cosmological transitions and about the quantization of cosmological perturbations.
14965415
Best unbiased estimators for the three point correlators of the cosmic microwave background radiation
Measuring the three-point correlators of the cosmic microwave background (CMB) anisotropies could help to get a handle on the level of non-Gaussianity present in the observational data sets and therefore would strongly constrain models of the early Universe. However, typically, the expected non-Gaussian signal is very small. Therefore, one has to face the problem of extracting it from the noise, in particular from the ``cosmic variance'' noise. For this purpose, one has to construct the best unbiased estimators for the three-point correlators that are needed for concrete detection of non-Gaussian features. In this article, we study this problem for both the CMB third moment and the CMB angular bispectrum. We emphasize that knowledge of the best estimator for the former does not permit one to infer the best estimator for the latter and vice versa. We present the corresponding best unbiased estimators in both cases and compute their corresponding cosmic variances.
24877696
A Variable Field Magnetic Extraction Channel for ORIC
An improved magnetic beam extraction channel for the Oak Ridge Isochronous Cyclotron (ORIC) has been designed to significantly reduce the external field disturbance and provide uniform in-channel field. This will make beam extraction near ¿r = 1 more predictable. The new channel consists of an iron tube of constant cross section with independently adjustable windings, both inside and outside the iron. The windings have a cos¿ current density distribution. The iron tube is 1 meter long with a bore of 6 cm; aperture for beam is 4 cm. The external field is negligible except for small perturbations in the field arising from the geometry modifications required at the ends so that the beam can enter and leave. The field reduction inside the channel is variable from 0.4 to 0.6 Tesla without significant change in either the internal field uniformity or the external field level.
110716676
A 4-MeV Experimental Separated-Orbit Cyclotron
A small experimental Separated-Orbit Cyclotron is being built to provide experience in the design and operation of this new type of accelerator. It will permit examination of the sensitivity of the SOC design to methods of construction and to errors in alignment. Some features are variable so that the flexibility of this class of machines for the acceleration of various particles and the applicability to high beam intensities can be evaluated.
42925836
Design Status of a Separated-Sector Cyclotron Booster Accelerator for the Holifield Heavy Ion Research Facility
A separated-sector cyclotron booster accelerator is being designed for the Holifield Heavy Ion Research Facility as a Phase II project to be started in 1978. Phase I of the HHIRF, now under construction, includes a 25 MV tandem electrostatic accelerator, a beam transport and injection system to enable use of the Oak Ridge Isochronous Cyclotron as an energy booster for tandem beams, and some additional experiment areas and associated beam transport systems. The Phase I facility using the ORIC-25 MV tandem combination will provide energies up to about 25 MeV/amu for light ions such as oxygen and more than 5 MeV/amu up to the region of mass 160. The new Phase II separated-sector cyclotron will provide energies up to 100 MeV/amu for light ions and up to 12 MeV/amu for the heaviest ions such as uranium.
117357855
Separated-sector cyclotron post-accelerator for the Oak Ridge Heavy Ion Laboratory
A separated sector cyclotron post-accelerator is proposed for the Oak Ridge Heavy Ion Laboratory. The SSC accepts beams from either ORIC or the 25 MV tandem electrostatic accelerator and extends the maximum particle energy to 75 MeV/u for A less than 40 and to at least 10 MeV/u for A greater than 40. The SSC has a field-radius product of 2540 kG-cm, a 4-sector configuration, and azimuthal pole width of 52°. RF acceleration of up to 1 MV per turn is obtained with two resonators in opposite valleys. An RF tuning range of 6 to 14 MHz accommodates acceleration on harmonics 2 through 11. Concentric second harmonic resonators are provided for optimizing phase acceptance.
28212230
Superconducting Conversion of the Oak Ridge Isochronous Cyclotron
The superconducting conversion of the Oak Ridge Isochronous Cyclotron (ORIC) will replace the existing aluminum main magnet coils with a NbTi superconducting coil system to provide an increase in magnetic field from 1.9 to 3.3 T. The higher magnetic field will provide a three-fold increase in maximum energy capability of the cyclotron for high mass ions. The conversion will include a new beam extraction system, magnet yoke stiffening to counteract the increased magnetic forces, and minor modifications to the beam transport systems and shielding.