Massless Metric Preheating

Can super-Hubble metric perturbations be amplified exponentially during preheating ? Yes. An analytical existence proof is provided by exploiting the conformal properties of massless inflationary models. The traditional conserved quantity \zeta is non-conserved in many regions of parameter space. We include backreaction through the homogeneous parts of the inflaton and preheating fields and discuss the role of initial conditions on the post-preheating power-spectrum. Maximum field variances are strongly underestimated if metric perturbations are ignored. We illustrate this in the case of strong self-interaction of the decay products. Without metric perturbations, preheating in this case is very inefficient. However, metric perturbations increase the maximum field variances and give alternative channels for the resonance to proceed. This implies that metric perturbations can have a large impact on calculations of relic abundances of particles produced during preheating.Comment: 8 pages, 4 colour figures. Version to appear in Phys. Rev. D. Contains substantial new analysis of the ranges of parameter space for which large changes to the inflation-produced power spectrum are expecte

Chandra Observations of Radio-Loud Quasars at z > 4: X-rays from the Radio Beacons of the Early Universe

We present the results of Chandra observations of six radio-loud quasars (RLQs) and one optically bright radio-quiet quasar (RQQ) at z = 4.1-4.4. These observations cover a representative sample of RLQs with moderate radio-loudness (R ~ 40-400), filling the X-ray observational gap between optically selected RQQs and the five known blazars at z > 4 (R ~ 800-27000). We study the relationship between X-ray luminosity and radio-loudness for quasars at high redshift and constrain RLQ X-ray continuum emission and absorption. From a joint spectral fit of nine moderate-R RLQs observed by Chandra, we find tentative evidence for absorption above the Galactic N_H, with a best-fit neutral intrinsic column density of N_H = 2.4^{+2.0}_{-1.8} x 10^{22} cm^{-2}, consistent with earlier claims of increased absorption toward high-redshift RLQs. We also search for evidence of an enhanced jet-linked component in the X-ray emission due to the increased energy density of the cosmic microwave background (CMB) at high redshift, but we find neither spatial detections of X-ray jets nor a significant enhancement in the X-ray emission relative to comparable RLQs at low-to-moderate redshifts. Overall, the z ~ 4-5 RLQs have basic X-ray properties consistent with comparable RLQs in the local universe, suggesting that the accretion/jet mechanisms of these objects are similar as well.Comment: 12 pages, The Astronomical Journal, in pres

Preheating of the nonminimally coupled inflaton field

We investigate preheating of an inflaton field $\phi$ coupled nonminimally to a spacetime curvature. In the case of a self-coupling inflaton potential $V(\phi)=\lambda \phi^4/4$, the dynamics of preheating changes by the effect of the negative $\xi$. We find that the nonminimal coupling works in two ways. First, since the initial value of inflaton field for reheating becomes smaller with the increase of $|\xi|$, the evolution of the inflaton quanta is delayed for fixed $\lambda$. Second, the oscillation of the inflaton field is modified and the nonadiabatic change around $\phi=0$ occurs significantly. That makes the resonant band of the fluctuation field wider. Especially for strong coupling regimes $|\xi| \gg 1$, the growth of the inflaton flutuation is dominated by the resonance due to the nonminimal coupling, which leads to the significant enhancement of low momentum modes. Although the final variance of the inflaton fluctuation does notchange significantly compared with the minimally coupled case, we have found that the energy transfer from the homogeneous inflaton to created particles efficiently occurs for $\xi<-60$.Comment: 13pages, 11figure

Testing for double inflation with WMAP

With the WMAP data we can now begin to test realistic models of inflation involving multiple scalar fields. These naturally lead to correlated adiabatic and isocurvature (entropy) perturbations with a running spectral index. We present the first full (9 parameter) likelihood analysis of double inflation with WMAP data and find that despite the extra freedom, supersymmetric hybrid potentials are strongly constrained with less than 7% correlated isocurvature component allowed when standard priors are imposed on the cosomological parameters. As a result we also find that Akaike & Bayesian model selection criteria rather strongly prefer single-field inflation, just as equivalent analysis prefers a cosmological constant over dynamical dark energy in the late universe. It appears that simplicity is the best guide to our universe.Comment: 7 pages, 6 figure

Condom use and the risk of HIV infection: who is being protected?

A study/survey done on condom use among Zimbabwean men in Zimbabwe.Descriptive baseline data at enrolment into a cohort of male factory workers who were tested for HIV serology and monitored for sero-con version over time, were analysed for condom use. At recruitment, the 1 146 men were asked about their sexual behaviour, history of sexually transmitted diseases (STDs), condom use and circumstances under which condoms were used. HIV seroprevalence in the cohort was 18,2 pc. Self reported use of condoms was low, with only 5 pc of the men reporting using them all the time. Forty four pc reported that they had never used a condom, 11,5 pc tried a condom only once, and 30,5 pc used condoms less than half the time. HIV positive men were more likely (Odds Ratio [OR]= 2,2 95 pc Cl: 1,3 — 3,3) to use condoms than those who tested negative. Men using a condom more than once were younger and had more education (p values < 0,0005). Univariate analysis showed that men with self reported risk factors for HIV infection were more likely to use condoms. Significantly more condom users reported paying for sex, multiple sex partners or (for married men) a girlfriend (p < 0,005). Condom users also more often had a history of genital ulcers, urethral discharge or other STDs. Few married men (24 pc) reported using a condom with their wives. Condom use was more commonly reported with commercial sex workers (44 pc) or other extramarital partners (36 pc). Some risk factors for HIV infection were also present amongst men who reported that they did not use condoms. Independent determinants of condom use identified by stepwise logistic regression analysis included young age, having a girlfriend (OR = 2,2; 95 pc Cl: 1,47 — 3,3), number of sex partners in the last year (OR = 1,27; 95 pc Cl: 1,06 —1,51 per partner), and paying for sex in the preceding year (OR = 1,74; 95 pc Cl: 1,06 — 2,83). The results show that men use condoms with partners considered risky, such as prostitutes or girlfriends but use condoms less often with their wives. The results underscore theneedfor health education for behavioural change that promotes universal, consistent use of condoms or monogamous partnership

Post-Inflationary Reheating

We study a model for reheating that has been much investigated for parametric resonance, having a quartic interaction of the scalar inflaton with another scalar field. Attention is particularly on the quantum excitations of the inflaton field and the metric perturbation with a smooth transition from quantum to classical stochastic states, followed through from a specific inflation model to a state including a relativistic fluid. The scalar fields enter non-perturbatively but the metric enters perturbatively, and the validity of this latter is assessed. In this model our work seems to point the large scale curvature parameter changing.Comment: 25 pages, 6 figures. Coding error(misprint) corrected:figures and some conclusions change