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.
119370816
Shift Symmetry and Inflation in Supergravity
We consider models of inflation in supergravity with a shift symmetry. We focus on models with one modulus and one inflaton field. The presence of this symmetry guarantees the existence of a flat direction for the inflaton field. Mildly breaking the shift symmetry using a superpotential which depends not only on the modulus, but also on the inflaton field allows one to lift the inflaton flat direction. Along the inflaton direction, the $\ensuremath{\eta}$ problem is alleviated. Combining the KKLT mechanism for modulus stabilization and a shift symmetry breaking superpotential of the chaotic inflation type, we find models reminiscent of ``mutated hybrid inflation'' where the inflationary trajectory is curved in the modulus-inflaton plane. We analyze the phenomenology of these models and stress their differences with both chaotic and hybrid inflation.
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.
118889842
Superimposed oscillations in the WMAP data
The possibility that the cosmic variance outliers present in the recently released Wilkinson Microwave Anisotropy Probe (WMAP) multipole moments are due to oscillations in the primordial power spectrum is investigated. Since the most important contribution to the WMAP likelihood originates from the outliers at a relatively small angular scale (around the first Doppler peak), special attention is paid to these in contrast with previous studies on the subject which have concentrated on the large scales outliers only (i.e., the quadrupole and octupole). As a physically motivated example, the case where the oscillations are of trans-Planckian origin is considered. It is shown that the presence of the oscillations causes an important drop in the WMAP χ2 of about 15. The F test reveals that such a drop has a probability less than 0.06% to occur by chance and can therefore be considered as statistically significant.
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.
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.
116322052
Accelerators for Heavy Ions
The use of heavy ion accelerators in nuclear physics, nuclear chemistry, atomic physics, and in material sciences studies is rapidly increasing. This paper reviews the present and developing scene in heavy ion accelerator concepts and technology. The area of applicability of various methods, likely avenues of future development and the trends of future requirements are discussed.
122793815
The 4-MeV Separated-Orbit Cyclotron
The Separated-Orbit Cyclotron Experiment (SOCE) will extend and complement earlier theoretical and experimental studies and will provide a unique facility for the evaluation of an operating SOC system. The six-sector, fourturn accelerator will provide maximum energies of 4 MeV for protons and deuterons and 8 MeV for 3He++ and 4He++ ions. The output energy is variable over a 2:1 range by adjustment of the magnetic field and acceleration of the ions at the appropriate harmonic of the ion frequency. Ions are injected into the SOC at one quarter the final energy. The injection system consists of a duoplasmatron ion source, a 500-kV dc accelerator, and a three-cavity linear accelerator. Proton currents in the 10-to 20-mA range are predicted. The principal characteristics of the accelerator are given in Table I. All of the major components have been fabricated and delivered on site except the injector's linac cavities, which are expected shortly. The photograph in Fig. 1 shows the accelerator as seen from the control area on a mezzanine about 40 feet away. The SOC sector magnets and rf cavities are in the approximate location, with the dc injector components in the background. The tops of the magnet yokes have been temporarily removed to permit completion of pole tip alignment. An rf power amplifier will be mounted on the outer wall of each cavity. One of the PA units can be seen in the background (Fig. 1) on a test stand with a water-cooled dummy load.
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.
122110697
The Holifield Heavy Ion Research Facility
The Holifield Heavy Ion Research Facility has been in routine operation since July 1982. Beams have been provided using both the tandem accelerator alone and a coupled mode in which the Oak Ridge Isochronous Cyclotron is used as an energy booster for tandem beams. The coupled mode has proved to be especially effective and has allowed us to provide a wide range of energetic beams for scheduled experiments. In this report we discuss our operational experience and recent development activities.
118797485
Initial operation of ORIC with tandem injection
Coupled operation of the 25 MV tandem and ORIC was achieved on January 27, 1981. The initial beam was 324 MeV /sup 16/O/sup 8 +/ followed shortly by oxygen at 400 MeV-the maximum design energy. Following additional installation and testing of the tandem, coupled operation for a nuclear physics experiment began in August. Performance of the system was in close agreement with that predicted from calculations.