Marie E. Machacek

TWO-LOOP RENORMALIZATION GROUP EQUATIONS IN A GENERAL QUANTUM FIELD THEORY

The two-loop renormalization group equations in a general renormalizable field theory with scalar, spin-12, and (vector) gauge fields are considered. In this paper, the anomalous dimensions associated with the wave function renormalizations of the fields are computed in a general Rξ gauge. The wave function renormalization of the gauge field in background field gauge, and hence the two-loop β function for the gauge coupling, are also evaluated.

Two-loop renormalization group equations in a general quantum field theory (II). Yukawa couplings

Abstract The two-loop β-functions for the Yukawa couplings are computed in a general renormalizable quantum field theory with scalar, spin 1 2 , and (vector) gauge fields associated with a general gauge group G. A more explicit form is given for the two-loop β-functions for the Yukawa couplings of the Higgs doublet in the minimal QCD-electroweak theory based on SU(3) × SU(2) × U(1).

SIMULATIONS OF PREGALACTIC STRUCTURE FORMATION WITH RADIATIVE FEEDBACK

We present results from three-dimensional hydrodynamic simulations of the high-redshift collapse of pregalactic clouds including feedback eUects from a soft photodissociating UV radiation —eld. The H 2 simulations use an Eulerian adaptive mesh re—nement technique to follow the nonequilibrium chemistry of nine chemical species with cosmological initial conditions drawn from a popular -dominated cold dark matter model. The results con—rm that the soft UV background can delay the cooling and collapse of small halos (D106 For reasonable values of the photodissociating —ux, the fraction is in M _ ). H 2 equilibrium throughout most of the objects we simulate. We determine the mass threshold for collapse for a range of soft-UV —uxes and also derive a simple analytic expression. Continuing the simulations beyond the point of initial collapse demonstrates that the fraction of gas which can cool depends mostly on the virial mass of the halo and the amount of soft-UV —ux, with remarkably little scatter. We parameterize this relation, for use in semianalytic models.

Two-loop renormalization group equations in a general quantum field theory: (III). Scalar quartic couplings

The two-loop β-functions for the scalar quartic couplings are computed in a general renormalizable quantum field theory with scalar, spin-12, and (vector) gauge fields associated with a general gauge group G, using dimensional regularization and modified minimal subtraction (−MS). A more explicit form is given for the two-loop β-function of the quartic coupling of the Higgs doublet in the minimal QCD electroweak theory based on SU(3) × SU(2) × U(1).

DOUBLY CHARGED HIGGS BOSONS

Abstract We explore through two simple models, the first in which scalars are treated as fundamental and the second in which they are composite objects, the possibility that representations containing doubly charged scalars may participate in the spontaneous breakdown of the SU(2) × U(1) symmetry of electroweak interactions. We show that such exotic Higgs bosons may posses unsuppressed coupling to pairs of gauge vector bosons and comment on the observability of these charged Higgs bosons through the Cahn-Dawson mechanism in high-energy hadron colliders.

Self-interacting dark matter

A new type of dark matter is considered. As with cold dark matter, when the dark matter is nonrelativistic, it does not couple to the electron-photon plasma, so its entropy per comoving volume is fixed. The new feature is that there is a cosmological era where number-changing reactions keep the dark matter in chemical equilibrium so that the chemical potential vanishes. This has several interesting consequences: during this era the dark matter cannibalizes its rest mass to keep warm, its temperature dropping only logarithmically with scale. We have done a general study of such self-interacting dark matter to identify the interesting ranges for its mass, coupling, and entropy. There are two consequences of this scheme which are particularly noteworthy. The unusual evolution of energy density and density perturbations allows for the possibility of decreasing the predicted anisotropies in the cosmic microwave background by a factor of 2 or more. This dark matter allows a completely new scheme for processing density perturbations. The theory introduces a new cosmological mass scale: the Jeans mass when the number-changing processes decouple. Perturbations on this supercluster scale are the first to go nonlinear.

Resolving the lyman-alpha forest

In this paper we critically examine predictions of the Lyα forest within the standard cold dark matter (SCDM) model, paying particular attention to the low end of the column-density distribution. We show in particular that the width of these lines, typically measured by the b-parameter of a Voigt profile, is sensitive to spatial resolution in numerical simulations and has previously been overestimated. The new result, which predicts a distribution with a median b of around 20-22 km s-1 at z=3, is substantially below that observed. We examine a number of possible causes of this discrepancy and argue that it is unlikely to be rectified by an increase in the thermal broadening of the absorbing gas but is instead telling us something about the distribution of matter on these scales. Although the median differs, the shape of the b-parameter distribution agrees quite well with that observed, and the high-end tail is naturally produced by the filamentary nature of gravitational collapse in these models. In particular, we demonstrate that lines of sight that obliquely intersect filaments or sheets tend to produce absorption lines with larger b parameters. We also examine the physical nature of the gas that is responsible for the forest, showing that for lines with neutral column densities below N~10 cm-2 (for this model at z=3), the peculiar infall velocity is actually slower than the Hubble flow, while larger lines have, on average, turned around and are collapsing.

The b Distribution of the Lyα Forest: Probing Cosmology and the Intergalactic Medium

We investigate a method for determining the temperature-density relation of the intergalactic medium (IGM) at z D 2¨4 using quasar absorption-line systems. Using a simple model combined with numerical simulations, we show that there is a lower cutoU in the distribution of column density and line (N H I ) width (b parameter). The location of this cutoU can be used to determine the temperature-density rela- tion (under certain conditions). We describe and test an algorithm to do this. The method works as long as the amplitude of —uctuations on these scales (D100 kpc) is sufficiently large. Models with less power can mimic higher temperatures. A preliminary application is made to data from two quasar lines of sight, and we determine an upper limit to the temperature of the IGM. Finally, we examine the full distribution of b parameters and show that this is completely speci—ed by just two: the temperature of the gas and the amplitude of the power spectrum. Using the temperature upper limit measured with the cutoU method, we derive an upper limit to the amplitude of the power spectrum. The limiting N H I -b uncertainty in this work appears to come from the nonunique nature of Voigt-pro—le —tting. Subject headings: cosmology: theoryintergalactic mediumquasars: absorption lines

Hydrodynamical simulations of the lyman alpha forest: model comparisons

We investigate the properties of the Lyα forest as predicted by numerical simulations for a range of currently viable cosmological models. This is done in order to understand the dependencies of the forest on cosmological parameters. Focusing on the redshift range from 2 to 4, we show that (1) most of the evolution in the distributions of optical depth, flux, and column density can be understood by simple scaling relations; (2) the shape of optical depth distribution is a sensitive probe of the amplitude of density fluctuations on scales of a few hundred kpc; and (3) the mean of the b distribution (a measure of the width of the absorption lines) is also very sensitive to fluctuations on these scales and decreases as they increase. We perform a preliminary comparison to observations, where available. A number of other properties are also examined, including the evolution in the number of lines, the two-point flux distribution, and the He II opacity.

Fermion and Higgs Masses as Probes of Unified Theories

Abstract The effects of Yukawa couplings of order of the gauge couplings in the SU(3) × SU(2) × U(1) renormalization group equations governing the evolution of observable parameters such as m b m τ and the Higgs mass are studied systematically to one-loop order. These parameters are found to give useful constraints on the mass of the t quark, and of possible heavier fermion families, in theories with SU(5)-like boundary conditions at unification energies.