Attractor Solution of Phantom Field

In light of recent study on the dark energy models that manifest an equation of state $w<-1$, we investigate the cosmological evolution of phantom field in a specific potential, exponential potential in this paper. The phase plane analysis show that the there is a late time attractor solution in this model, which address the similar issues as that of fine tuning problems in conventional quintessence models. The equation of state $w$ is determined by the attractor solution which is dependent on the $\lambda$ parameter in the potential. We also show that this model is stable for our present observable universe.Comment: 9 pages, 3 ps figures; typos corrected, references updated, this is the final version to match the published versio

Renormalization-group running of the cosmological constant and its implication for the Higgs boson mass in the Standard Model

The renormalization-group equation for the zero-point energies associated with vacuum fluctuations of massive fields from the Standard Model is examined. Our main observation is that at any scale the running is necessarily dominated by the heaviest degrees of freedom, in clear contradistinction with the Appelquist & Carazzone decoupling theorem. Such an enhanced running would represent a disaster for cosmology, unless a fine-tuned relation among the masses of heavy particles is imposed. In this way, we obtain $m_H \simeq 550 GeV$ for the Higgs mass, a value safely within the unitarity bound, but far above the more stringent triviality bound for the case when the validity of the Standard Model is pushed up to the grand unification (or Planck) scale.Comment: 11 pages, LaTex2

Metabolism of alcaligenes denitrificans in biofilm vs planktonic cells

Aims: To compare the effect of phosphorous concentration (200 mg P 1-1 and 20 mg P 1-1) on the denitrifying efficiency of Alcaligenes denitrificans when in the form of planktonic cells or in the form of a biofilm, and to select the most adequate C/N ratio. Methods and Results: Two types of assays were carried out: with planktonic cells and with cells in biofilm form. Anoxic bottles with the appropriate C/N and phosphorous concentration were incubated at 30°C and submitted to orbital shaking at 150 rev min-1. The specific activity of cells in biofilm form, in terms of substrate consumption, was significantly higher than cells in planktonic form. With regard to the effect of increasing phosphorous concentration, an increase in specific activity was also only evident when the cells were in biofilm form. Conclusions: The two forms showed different performances and phosphorous concentration only markedly affected the biofilm form. Significance and Impact of the Study: The importance of the C/N/P ratio in the denitrification process is demonstrated. As there was no report in the literature about the stoichiometric relationship of heterotrophic denitrification with citrate, its stoichiometry, including the requirement for cell synthesis, was determined.Instituto de Biotecnologia e Química Fina (IBQF). PRAXIS XXI

A Symmetry for the Cosmological Constant

We study a symmetry, schematically Energy -> - Energy, which suppresses matter contributions to the cosmological constant. The requisite negative energy fluctuations are identified with a "ghost" copy of the Standard Model. Gravity explicitly, but weakly, violates the symmetry, and naturalness requires General Relativity to break down at short distances with testable consequences. If this breakdown is accompanied by gravitational Lorentz-violation, the decay of flat spacetime by ghost production is acceptably slow. We show that inflation works in our scenario and can lead to the initial conditions required for standard Big Bang cosmology.Comment: 18 pages, 3 figures, References correcte

Search for an annual modulation of dark-matter signals with a germanium spectrometer at the Sierra Grande Laboratory

Data collected during three years with a germanium spectrometer at the Sierra Grande underground laboratory have been analyzed for distinctive features of annual modulation of the signal induced by WIMP dark matter candidates. The main motivation for this analysis was the recent suggestion by the DAMA/NaI Collaboration that a yearly modulation signal could not be rejected at the 90% confidence level when analyzing data obtained with a high-mass low-background scintillator detector. We performed two different analyses of the data: First, the statistical distribution of modulation-significance variables (expected from an experiment running under the conditions of Sierra Grande) was compared with the same variables obtained from the data. Second, the data were analyzed in energy bins as an independent check of the first result and to allow for the possibility of a crossover in the expected signal. In both cases no statistically significant deviation from the null result was found, which could support the hypothesis that the data contain a modulated component. A plot is also presented to enable the comparison of these results to those of the DAMA collaboration.Comment: New version accepted by Astroparticle Physics. Changes suggested by the referee about the theoretical prediction of rates are included. Conclusions remain unaffected. 14 pages, LaTeX, 7 figures. Uses epsfig macr

The Influence of Free Quintessence on Gravitational Frequency Shift and Deflection of Light with 4D momentum

Based on the 4D momentum, the influence of quintessence on the gravitational frequency shift and the deflection of light are examined in modified Schwarzschild space. We find that the frequency of photon depends on the state parameter of quintessence $w_q$: the frequency increases for $-1<w_q<-1/3$ and decreases for $-1/3<w_q<0$. Meanwhile, we adopt an integral power number $a$ ($a = 3\omega_q + 2$) to solve the orbital equation of photon. The photon's potentials become higher with the decrease of $\omega_q$. The behavior of bending light depends on the state parameter $\omega_q$ sensitively. In particular, for the case of $\omega_q = -1$, there is no influence on the deflection of light by quintessence. Else, according to the H-masers of GP-A redshift experiment and the long-baseline interferometry, the constraints on the quintessence field in Solar system are presented here.Comment: 12 pages, 2 figures, 4 tables. European Physical Journal C in pres

Potential for Supernova Neutrino Detection in MiniBooNE

The MiniBooNE detector at Fermilab is designed to search for $\nu_\mu \to \nu_e$ oscillation appearance at $E_\nu \sim 1 {\rm GeV}$ and to make a decisive test of the LSND signal. The main detector (inside a veto shield) is a spherical volume containing 0.680 ktons of mineral oil. This inner volume, viewed by 1280 phototubes, is primarily a \v{C}erenkov medium, as the scintillation yield is low. The entire detector is under a 3 m earth overburden. Though the detector is not optimized for low-energy (tens of MeV) events, and the cosmic-ray muon rate is high (10 kHz), we show that MiniBooNE can function as a useful supernova neutrino detector. Simple trigger-level cuts can greatly reduce the backgrounds due to cosmic-ray muons. For a canonical Galactic supernova at 10 kpc, about 190 supernova $\bar{\nu}_e + p \to e^+ + n$ events would be detected. By adding MiniBooNE to the international network of supernova detectors, the possibility of a supernova being missed would be reduced. Additionally, the paths of the supernova neutrinos through Earth will be different for MiniBooNE and other detectors, thus allowing tests of matter-affected mixing effects on the neutrino signal.Comment: Added references, version to appear in PR

Ghost D-branes

We define a ghost D-brane in superstring theories as an object that cancels the effects of an ordinary D-brane. The supergroups U(N|M) and OSp(N|M) arise as gauge symmetries in the supersymmetric world-volume theory of D-branes and ghost D-branes. A system with a pair of D-brane and ghost D-brane located at the same location is physically equivalent to the closed string vacuum. When they are separated, the system becomes a new brane configuration. We generalize the type I/heterotic duality by including n ghost D9-branes on the type I side and by considering the heterotic string whose gauge group is OSp(32+2n|2n). Motivated by the type IIB S-duality applied to D9- and ghost D9-branes, we also find type II-like closed superstrings with U(n|n) gauge symmetry.Comment: 49 pages, 6 figures, harvmac. v2: references and acknowledgements adde

Can R-parity violation explain the LSND data as well?

The recent Super-Kamiokande data now admit only one type of mass hierarchy in a framework with three active and one sterile neutrinos. We show that neutrino masses and mixings generated by R-parity-violating couplings, with values within their experimental upper limits, are capable of reproducing this hierarchy, explaining all neutrino data particularly after including the LSND results.Comment: 7 pages, Latex, 3 PS figures; in v2 a few clarifying remarks included and two references added (to appear in Physical Review D

Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data

We present a unified global analysis of neutrino oscillation data within the framework of the four-neutrino mass schemes (3+1) and (2+2). We include all data from solar and atmospheric neutrino experiments, as well as information from short-baseline experiments including LSND. If we combine only solar and atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas short-baseline data in combination with atmospheric data prefers (2+2) models. When combining all data in a global analysis the (3+1) mass scheme gives a slightly better fit than the (2+2) case, though all four-neutrino schemes are presently acceptable. The LSND result disfavors the three-active neutrino scenario with only $\Delta m^2_{sol}$ and $\Delta m^2_{atm}$ at 99.9% CL with respect to the four-neutrino best fit model. We perform a detailed analysis of the goodness of fit to identify which sub-set of the data is in disagreement with the best fit solution in a given mass scheme.Comment: 32 pages, 8 Figures included, REVTeX4.Improved discussion in sec. XI, references added, version accepted by Phys. Rev.