Investigation of a0-f0 mixing

We investigate the isospin-violating mixing of the light scalar mesons a0(980) and f0(980) within the unitarized chiral approach. Isospin-violating effects are considered to leading order in the quark mass differences and electromagnetism. In this approach both mesons are generated through meson-meson dynamics. Our results provide a description of the mixing phenomenon within a framework consistent with chiral symmetry and unitarity, where these resonances are not predominantly q q-bar states. Amongst the possible experimental signals, we discuss observable consequences for the reaction J/Psi -> phi pi0 eta in detail. In particular we demonstrate that the effect of a0-f0 mixing is by far the most important isospin-breaking effect in the resonance region and can indeed be extracted from experiment.Comment: 15 pages, 9 figures; discussion extended, title changed, version published in Phys. Rev.

Cosmological neutrino bounds for non-cosmologists

I briefly review cosmological bounds on neutrino masses and the underlying gravitational physics at a level appropriate for readers outside the field of cosmology. For the case of three massive neutrinos with standard model freezeout, the current 95% upper limit on the sum of their masses is 0.42 eV. I summarize the basic physical mechanism making matter clustering such a sensitive probe of massive neutrinos. I discuss the prospects of doing still better in coming years using tools such as lensing tomography, approaching a sensitivity around 0.03 eV. Since the lower bound from atmospheric neutrino oscillations is around 0.05 eV, upcoming cosmological measurements should detect neutrino mass if the technical and fiscal challenges can be met.Comment: 4 pages, 2 figs, in "Neutrino Physics", Proceedings of Nobel Symposium 129, eds., L Bergstrom, O. Botner, P. Carlson, P. O. Hulth, and T. Ohlsso

Cosmological mass limits on neutrinos, axions, and other light particles

The small-scale power spectrum of the cosmological matter distribution together with other cosmological data provides a sensitive measure of the hot dark matter fraction, leading to restrictive neutrino mass limits. We extend this argument to generic cases of low-mass thermal relics. We vary the cosmic epoch of thermal decoupling, the radiation content of the universe, and the new particle's spin degrees of freedom. Our treatment covers various scenarios of active plus sterile neutrinos or axion-like particles. For three degenerate massive neutrinos, we reproduce the well-known limit of m_nu < 0.34 eV. In a 3+1 scenario of 3 massless and 1 fully thermalized sterile neutrino we find m_nu < 1.0 eV. Thermally produced QCD axions must obey m_a < 3.0 eV, superseding limits from a direct telescope search, but leaving room for solar eV-mass axions to be discovered by the CAST experiment.Comment: 15 pages, 6 figures, matches version in JCA

Ultra-High Energy Cosmic Rays and Stable H-dibaryon

It is shown that an instanton induced interaction between quarks produces a very deeply bound H-dibaryon with mass below 2M_N, M_H=1718 MeV. Therefore the H-dibaryon is predicted to be a stable particle. The reaction of photodisintegration of H-dibaryon to $2\Lambda$ in during of its penetration into cosmic microwave background will result in a new possible cut-off in the cosmic-ray spectrum. This provides an explanation of ultra-high energy cosmic ray events observed above the GZK cut-off as a result of the strong interaction of high energy H-dibaryons from cosmic rays with nuclei in Earth's atmosphere.Comment: 5 pages, Late

The Halo Mass Function: High-Redshift Evolution and Universality

We study the formation of dark matter halos in the concordance LCDM model over a wide range of redshifts, from z=20 to the present. Our primary focus is the halo mass function, a key probe of cosmology. By performing a large suite of nested-box N-body simulations with careful convergence and error controls (60 simulations with box sizes from 4 to 256 Mpc/h, we determine the mass function and its evolution with excellent statistical and systematic errors, reaching a few percent over most of the considered redshift and mass range. Across the studied redshifts, the halo mass is probed over 6 orders of magnitude (10^7 - 10^13.5 M_sun/h). Historically, there has been considerable variation in the high redshift mass function as obtained by different groups. We have made a concerted effort to identify and correct possible systematic errors in computing the mass function at high redshift and to explain the discrepancies between some of the previous results. We discuss convergence criteria for the required force resolution, simulation box size, halo mass range, initial and final redshift, and time stepping. Because of conservative cuts on the mass range probed by individual boxes, our results are relatively insensitive to simulation volume, the remaining sensitivity being consistent with extended Press-Schechter theory. Previously obtained mass function fits near z=0, when scaled by linear theory, are in good agreement with our results at all redshifts, although a mild redshift dependence consistent with that found by Reed and collaborators exists at low redshifts.Comment: 20 pages, 15 figures. Minor changes to the text and figures; results and conclusions unchange

The Cosmic Neutrino Background and the Age of the Universe

We discuss the cosmological degeneracy between the age of the Universe, the Hubble parameter and the effective number of relativistic particles N_eff. We show that independent determinations of the Hubble parameter H(z) as those recently provided by Simon,Verde, Jimenez (2006), combined with other cosmological data sets can provide the most stringent constraint on N_eff, yielding N_eff=3.7 (-1.2) (+1.1) at 95% confidence level. A neutrino background is detected with high significance: N_eff >1.8 at better than 99% confidence level. Constraints on the age of the universe in the framework of an extra background of relativistic particles are improved by a factor 3.Comment: JCAP, in pres

Casimir Effects in Renormalizable Quantum Field Theories

We review the framework we and our collaborators have developed for the study of one-loop quantum corrections to extended field configurations in renormalizable quantum field theories. We work in the continuum, transforming the standard Casimir sum over modes into a sum over bound states and an integral over scattering states weighted by the density of states. We express the density of states in terms of phase shifts, allowing us to extract divergences by identifying Born approximations to the phase shifts with low order Feynman diagrams. Once isolated in Feynman diagrams, the divergences are canceled against standard counterterms. Thus regulated, the Casimir sum is highly convergent and amenable to numerical computation. Our methods have numerous applications to the theory of solitons, membranes, and quantum field theories in strong external fields or subject to boundary conditions.Comment: 27 pp., 11 EPS figures, LaTeX using ijmpa1.sty; email correspondence to R.L. Jaffe ; based on talks presented by the authors at the 5th workshop `QFTEX', Leipzig, September 200