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.
18840537
Predictions of inflation: the slow roll approximation vs. exact results
Inflation predicts the generation of cosmological perturbations. Usually, the power spectra for the scalar and tensor modes are calculated with help of the slow roll approximation. In the case of power law inflation an exact result is available. We compare the predictions for the cosmic microwave background anisotropies from the slow roll approximation with the exact results from power law inflation. We find that the so-called consistency check from the slow roll approximation, $C_2^T/C_2^S \approx -6.93 n_T$, may differ considerably from the exact result.
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.
13505150
The Stress energy tensor for transPlanckian cosmology
This article presents the derivation of the stress-energy tensor of a free scalar field with a general non-linear dispersion relation in curved spacetime. This dispersion relation is used as a phenomelogical description of the short distance structure of spacetime following the conventional approach of trans-Planckian modes in black hole physics and in cosmology. This stress-energy tensor is then used to discuss both the equation of state of trans-Planckian modes in cosmology and the magnitude of their backreaction during inflation. It is shown that gravitational waves of trans-Planckian momenta but subhorizon frequencies cannot account for the form of cosmic vacuum energy density observed at present, contrary to a recent claim. The backreaction effects during inflation are confirmed to be important and generic for those dispersion relations that are liable to induce changes in the power spectrum of metric fluctuations. Finally, it is shown that in pure de Sitter inflation there is no modification of the power spectrum except for a possible magnification of its overall amplitude independently of the dispersion relation.
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.
125516191
Alternates to the cyclotron for heavy-ion acceleration.
The status and future possibilities for several alternates to the cyclotron for heavy‐ion acceleration are discussed. Linear accelerators, both conventional and superconducting, tandem electrostatic accelerators, and the electron ring accelerator are among the accelerator types and concepts reviewed and compared.
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.
115550416
RECENT PROGRESS ON A SUPERCURRENT SEPARATED ORBIT CYCLOTRON.
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.
93888470
Design Study for the Conversion of the Oak Ridge Isochronous Cyclotron from an Energy Constant of K=90 to K=300 MeV
A possible method of achieving a K=300 MeV cyclotron by increasing the average magnetic field of the Oak Ridge Isochronous Cyclotron (ORIC) from 18.6 to 33.9 kG with superconducting coils has been investigated.