The Landau gauge Schwinger-Dyson Equation for the quark self-energy is solved in the quenched ladder approximation for several cases of one- and two-quark-generations. The exchanges of Standard Model gluons and Higgs bosons are taken into account. It is found that Higgs boson exchange dominates the quark self-energy for sufficiently large input quark masses (>75 GeV), causing the running quark propagator mass to increase with energy-scale. The running of the quark mixing angles is also considered. No running of the quark mixing angles is found, to one part in a billion, for input quark masses up to and including 500 GeV.
We introduce a data analysis procedure for color transparency experiments which is considerably less model dependent than the transparency ratio method. The new method is based on fitting the shape of the A dependence of the nuclear cross section at fixed momentum transfer to determine the effective attenuation cross section for hadrons propagating through the nucleus. The hard scattering cross section is then determined directly from the data. We apply this procedure to the Brookhaven experiment of Carroll et al and find that it clearly shows color transparency: the effective attenuation cross section in events with momentum transfer $Q^2$ is approximately $40 mb (2.2 GeV^2/Q^2)$. The fit to the data also supports the idea that the hard scattering inside the nuclear medium is closer to perturbative QCD predictions than is the scattering of isolated protons in free space. We discuss the application of our approach to electroproduction experiments.
We study the excess 1-3 GeV gamma rays signal observed from the galactic center within a conformal model. The model has a dark sector with strong self interactions. This sector couples weakly with the Standard Model particles via a scalar messenger. The lightest dark sector particle is a pion-like fermion anti-fermion bound state. We find that the observed gamma ray excess at Fermi-LAT is nicely explained in terms of decay of the dark pions. The dark matter relic density is also explained by the freeze-in mechanism in which the dark pions are produced in the early Universe by annihilation and decay of standard model particles. We have used Higgs invisible decay and dark matter direct detection experiments in order to put bounds on the parameters of the model.
The coupled Bethe-Salpeter bound state equations for a $Q\overline{Q}$ system, where $Q=(U,D)$ is a degenerate, fourth generation, superheavy quark doublet, are solved in several ladder approximation models. The exchanges of gluon, Higgs, and Goldstone modes in the standard model are calculated in the ultraheavy quark limit where weak $\ensuremath{\gamma}$, ${W}^{\ifmmode\pm\else\textpm\fi{}}$, and ${Z}^{0}$ contributions are negligible. A natural $I=0$ and $I=1$ multiplet pattern is found, with large splittings occurring between the different weak isospin states when ${M}_{Q}$, the quark masses, are larger than values in the range $0.4 \mathrm{TeV}<{M}_{Q}<0.8 \mathrm{TeV}$, depending on which model is used. Consideration of ultraheavy quark lifetime constraints and $U\ensuremath{-}D$ mass splitting constraints are reviewed to establish the plausibility of lifetime and mass degeneracy requirements assumed for this paper.
We investigate the contribution of technicolor mechanisms to the production of single top quarks at hadron colliders. We find that a promising candidate process is gluon-gluon fusion to produce a W-boson plus technipion, with subsequent decay of the technipion to a top quark plus a bottom quark. The top-plus-bottom mode is the dominant one when the technipion mass is larger than the top mass. We calculate the total cross section and the $p_{T}$ distribution for the technipion production at Tevatron and LHC energies for a range of technipion masses, starting at 200 GeV. The decay chain of technipion to top plus bottom quarks and then top to W plus bottom yields a final state with two W's and two bottom quarks. We study the backgrounds to our process and the kinematic cuts that maximize the signal to background. We report event rate estimates for the upgraded Tevatron and the LHC.
We study the $SU(3)_L\otimes U(1)_X$ extension of the Standard model with a strong U(1) coupling. We argue that current experiments limit this coupling to be relatively large. The model is dynamically broken to the Standard $SU(2)_L \otimes U(1)$ model at the scale of a few TeV with all the extra gauge bosons and the exotic quarks acquiring masses much larger than the scale of electroweak symmetry breaking. Furthermore we find that the model leads to large dynamical mass of the top quark and hence also breaks the electroweak gauge symmetry. It therefore leads to large dynamical effects within the Standard model and can partially replace the Higgs interactions.
We investigate the contribution of technicolor mechanisms to the production of single top quarks at hadron colliders. Technipions with a mass larger than the top quark mass will decay predominantly to a top quark plus a bottom antiquark. We investigate two promising subprocesses: color-octet technipion plus a $W$ boson via gluon-gluon fusion and technipion plus quark production via quark gluon interaction. The decay chain of a technipion to a top quark plus bottom quarks and then a top quark to a $W$ plus bottom yields final states for the two subprocesses with, respectively, two $W$'s and two bottom quarks and one $W,$ two bottom quarks, and a light quark. We calculate the total cross sections and the ${p}_{T}$ distributions for these technipion production mechanisms at CERN LHC energies for a range of technipion masses, starting at 200 GeV. We study the backgrounds to our processes and the kinematic cuts that enhance the signal to background ratio and we report event rate estimates for the upgraded Fermilab Tevatron and the LHC. Only the LHC has the potential to observe these processes.
We develop a general formalism to treat reflection of spherical electromagnetic waves from a spherical surface. Our main objective is interpretation of radio wave signals produced by cosmic ray interactions with Earth's atmosphere which are observed by the Antarctica based ANITA detector after reflection off the ice surface. The incident wave is decomposed into plane waves and each plane wave is reflected off the surface using the standard Fresnel formalism. For each plane wave the reflected wave is assumed to be locally a plane wave. This is a very reasonable assumption and there are no uncontrolled approximations in our treatment of the reflection phenomenon. The surface roughness effects are also included by using a simple model. We apply our formalism to the radiation produced by the balloon-borne HiCal radio-frequency (RF) transmitter. Our final results for the reflected power are found to be in good agreement with data for all elevation angles.
We study the energy and nuclear A dependence of the hadronic production of heavy quarkonia. We review theoretical ideas which have been put forward, seeking a consistent global picture reconciling the large effects in quarkonia with the small nuclear effects observed in continuum Drell Yan production. The data indicates that shadowing or leading twist modifications of parton distributions can be ruled out as explanations, leaving higher twist energy loss. {}From general principles the maximum allowed energy loss of partons traversing the nuclear medium can be related to the parton transverse momenta. We then show that the experimental data on nuclear suppression of charm- and bottom- onium for large $x_F$ is consistent with this effect: using the observed transverse momenta to bound the $x_F$ dependence in an almost model independent manner generates a relation that practically reproduces the data. Several prediction are discussed; the dependence on $x_F$ as $x_F\to 1$, and large and small $k_T^2$ cuts, can be used to discriminate between quark and gluon induced effects.
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