Deformation effects in Giant Monopole Resonance

The isoscalar giant monopole resonance (GMR) in Samarium isotopes (from spherical $^{144}$Sm to deformed $^{148-154}$Sm) is investigated within the Skyrme random-phase-approximation (RPA) for a variety of Skyrme forces. The exact RPA and its separable version (SRPA) are used for spherical and deformed nuclei, respectively. The quadrupole deformation is shown to yield two effects: the GMR broadens and attains a two-peak structure due to the coupling with the quadrupole giant resonance.Comment: 6 pages, 4 figures, proceedings of 11th Intern. Spring Seminar on Nuclear Physics (Ischia, Italy, May 12-16, 2014

Critical Charges on Strange Quark Nuggets and Other Extended Objects

We investigate the behavior of the critical charge for spontaneous pair production, $Z_C$, defined as the charge at which the total energy of a $K$-shell electron is $E=-m_e$, as a function of the radius $R$ of the charge distribution. Our approach is to solve the Dirac equation for a potential $V(r)$ consisting of a spherically symmetrical charge distribution of radius $R$ and a Coulomb tail. For a spherical shell distribution of the type usually associated with color-flavor locked strange quark nuggets, we confirm the relation $Z_C=0.71 R({\rm fm})$ for sufficiently large $R$ obtained by Madsen, who used an approach based on the Thomas-Fermi model. We also present results for a uniformly charged sphere and again find that $Z_C\sim R$ for large enough $R$. Also discussed is the behavior of $Z_C$ when simple {\it ad hoc} modifications are made to the potential for $0\leq r < R$.Comment: 7 pages, 6 figure

A note on the rare decay of a Higgs boson into photons and a ZZ boson

We have calculated the width of the rare decay $H\to\gamma\gamma Z$ at one-loop level in the standard model for Higgs boson masses in the range $115 {\rm GeV} \leq m_H \leq 160 {\rm GeV}$ . For this range of Higgs boson masses we find that $Z$ boson is predominantly longitudinally polarized, and the photons have the same helicity. A comparison of the decay width $\Gamma(H\to \gamma\gamma Z)$ to those of $H\to\gamma\gamma$ and $H\to\gamma Z$ shows that, for the Higgs boson mass of $m_H \sim 135 \rm{GeV}$, the ratios of the decay widths are $\Gamma(H\to\gamma\gamma Z) / \Gamma(H\to\gamma\gamma) \sim \Gamma(H\to\gamma\gamma Z) / \Gamma(H\to\gamma Z) \sim 10^{-5}-10^{-6}$.Comment: 4 pages, 5 figures, RevTe

High energy photon-neutrino elastic scattering

The one-loop helicity amplitudes for the elastic scattering process $\gamma\nu\to\gamma\nu$ in the Standard Model are computed at high center of mass energies. A general decomposition of the amplitudes is utilized to investigate the validity of some of the key features of our results. In the center of mass, where $\sqrt{s} = 2\omega$, the cross section grows roughly as $\omega^6$ to near the threshold for $W$-boson production, $\sqrt{s} = m_W$. Although suppressed at low energies, we find that the elastic cross section exceeds the cross section for $\gamma\nu\to\gamma\gamma\nu$ when $\sqrt{s}>13$ GeV. We demonstrate that the scattered photons are circularly polarized and the net value of the polarization is non-zero. Astrophysical implications of high energy photon-neutrino scattering are discussed.Comment: 9 pages, 7 figures, RevTeX

Constraints on the dark energy equation of state from recent supernova data

Measurements suggest that our universe has a substantial dark energy component. The most recent data on type Ia supernovae give a dark energy density which is in good agreement with other measurements if the dark energy is assumed to be a cosmological constant. Here we examine to what extent that data can put constraints on a more general equation of state for the dark energy.Comment: Journal version with additional reference

gamma nu -> gamma gamma nu and crossed processes at energies below m_W

The cross sections for the processes $\gamma \nu\to \gamma \gamma \nu$, $\gamma\gamma\to\gamma\nu\bar{\nu}$ and $\nu\bar{\nu}\to\gamma\gamma\gamma$ are calculated for a range of center of mass energies from below $m_e$ to considerably above $m_e$, but much less than $m_W$. This enables us to treat the neutrino--electron coupling as a four--Fermi interaction and results in amplitudes which are electron box diagrams with three real photons and one virtual photon at their vertices. These calculations extend our previous low--energy effective interaction results to higher energies and enable us to determine where the effective theory is reliable.Comment: 12 pages, RevTex, 10 postscript figures include

Higgs-photon associated production at eeˉe\bar{e} colliders

We present complete analytical expressions for the amplitudes of the process $e\bar{e}\rightarrow H\gamma$. The calculation is performed using nonlinear gauges, which significantly simplifies both the actual analytical calculation and the check of its gauge invariance. After comparing our results with a previous numerical calculation, we extend the range of Higgs masses and center of mass energies to those appropriate to LEP 200 and a future linear collider.Comment: To appear in PRD. 18 pages latex, uses REVTEX; 5 postscript figure

Charges on Strange Quark Nuggets in Space

Since Witten's seminal 1984 paper on the subject, searches for evidence of strange quark nuggets (SQNs) have proven unsuccessful. In the absence of experimental evidence ruling out SQNs, the validity of theories introducing mechanisms that increase their stability should continue to be tested. To stimulate electromagnetic SQN searches, particularly space searches, we estimate the net charge that would develop on an SQN in space exposed to various radiation baths (and showers) capable of liberating their less strongly bound electrons, taking into account recombination with ambient electrons. We consider, in particular, the cosmic background radiation, radiation from the sun, and diffuse galactic and extragalactic $\gamma$-ray backgrounds. A possible dramatic signal of SQNs in explosive astrophysical events is noted.Comment: CitationS added, new subsection added, more discussion, same numerical result

Photons, neutrinos and large compact space dimensions

We compute the contribution of Kaluza-Klein graviton exchange to the cross section for photon-neutrino scattering. Unlike the usual situation where the virtual graviton exchange represents a small correction to a leading order electroweak or strong amplitude, in this case the graviton contribution is of the same order as the electroweak amplitude, or somewhat larger. Inclusion of the graviton contribution is not sufficient to allow high energy neutrinos to scatter from relic neutrinos in processes such as $\nu\bar{\nu}\to\gamma\gamma$, but the photon-neutrino decoupling temperature is substantially reduced.Comment: 8 pages, 3 figures LaTeX. Typos correcte