In the standard slow-roll inflationary cosmology, quantum fluctuations in a single field, the inflaton, generate approximately Gaussian primordial density perturbations. At present, the bispectrum and trispectrum of the density perturbations have not
been observed and the probability distribution for these perturbations is consistent with Gaussianity. However, Planck satellite data will bring a new level of precision to bear on this issue, and it is possible that evidence for non-Gaussian effects in the primordial distribution will be discovered. One possibility is that a trispectrum will be observed without evidence for a non-zero bispectrum. It is not difficult for this to occur in inflationary models where quantum fluctuations in a field other than the inflaton contribute to the density perturbations. A natural question to ask is whether such an observation would rule out the standard scenarios. We explore this issue and find that it is possible to construct single-field models in which inflaton-generated primordial density perturbations have an observable trispectrum, but a bispectrum that is too small to be observed by the Planck satellite. However, an awkward fine tuning seems to be unavoidable.
We investigate the dark matter and the cosmological baryon asymmetry in a simple theory where baryon (B) and lepton (L) number are local gauge symmetries that are spontaneously broken. In this model, the cold dark matter candidate is the lightest new
field with baryon number and its stability is an automatic consequence of the gauge symmetry. Dark matter annihilation is either through a leptophobic gauge boson whose mass must be below a TeV or through the Higgs boson. Since the mass of the leptophobic gauge boson has to be below the TeV scale one finds that in the first scenario there is a lower bound on the elastic cross section of about 5x10^{-46} cm^2. Even though baryon number is gauged and not spontaneously broken until the weak scale, a cosmologically acceptable baryon excess is possible. There is tension between achieving both the measured baryon excess and the dark matter density.
Primordial quantum fluctuations produced by inflation are conventionally assumed to be statistically homogeneous, a consequence of translational invariance. In this paper we quantify the potentially observable effects of a small violation of translat
ional invariance during inflation, as characterized by the presence of a preferred point, line, or plane. We explore the imprint such a violation would leave on the cosmic microwave background anisotropy, and provide explicit formulas for the expected amplitudes $<a_{lm}a_{lm}^*>$ of the spherical-harmonic coefficients.
New resonances with masses of order a few ${rm TeV}$ might be discovered at the LHC. We show that no resonance that couples to electrons only through Standard Model interactions can decay to both $e^+e^-$and $gamma gamma$ with significant branching r
atios. This means that finding both electron-positron and two-photon final states is evidence that electrons couple directly to the new physics associated with the resonance and furthermore that the resonance is not spin-1. The least fine-tuned such examples involve electron compositeness. One such example, Kaluza Klein excitations of the graviton in the version of the Randall Sundrum Model where Standard Model matter is located on the ${rm TeV}$ brane, can be distinguished from other possibilities by its predicted branching fractions into the two modes.
First passage models, where corporate assets undergo correlated random walks and a company defaults if its assets fall below a threshold provide an attractive framework for modeling the default process. Typical one year default correlations are small
, i.e., of order a few percent, but nonetheless including correlations is very important, for managing portfolio credit risk and pricing some credit derivatives (e.g. first to default baskets). In first passage models the exact dependence of the joint survival probability of more than two firms on their asset correlations is not known. We derive an expression for the dependence of the joint survival probability of $n$ firms on their asset correlations using first order perturbation theory in the correlations. It includes all terms that are linear in the correlations but neglects effects of quadratic and higher order. For constant time independent correlations we compare the first passage model expression for the joint survival probability with what a multivariate normal Copula function gives. As a practical application of our results we calculate the dependence of the five year joint survival probability for five basic industrials on their asset correlations.
We study the classical stability of an anisotropic space-time seeded by a spacelike, fixed norm, dynamical vector field in a vacuum-energy-dominated inflationary era. It serves as a model for breaking isotropy during the inflationary era. We find tha
t, for a range of parameters, the linear differential equations for small perturbations about the background do not have a growing mode. We also examine the energy of fluctuations about this background in flat-space. If the kinetic terms for the vector field do not take the form of a field strength tensor squared then there is a negative energy mode and the background is unstable. For the case where the kinetic term is of the form of a field strength tensor squared we show that perturbations about the background have positive energy at lowest order.
In quantum mechanics the deterministic property of classical physics is an emergent phenomenon appropriate only on macroscopic scales. Lee and Wick introduced Lorentz invariant quantum theories where causality is an emergent phenomenon appropriate fo
r macroscopic time scales. In this paper we analyze a Lee-Wick version of the O(N) model. We argue that in the large N limit this theory has a unitary and Lorentz invariant S matrix and is therefore free of paradoxes in scattering experiments. We discuss some of its acausal properties.
We show that there are regions of parameter space in multi-scalar doublet models where, in the first few hundred inverse femtobarns of data, the new charged and neutral scalars are not directly observable at the LHC and yet the Higgs decay rate to b
bbar is changed significantly from its standard model value. For a light Higgs with a mass less than 140 GeV, this can cause a large change in the number of two photon and tau tau Higgs decay events expected at the LHC compared to the minimal standard model. In the models we consider, the principle of minimal flavor violation is used to suppress flavor changing neutral currents. This paper emphasizes the importance of measuring the properties of the Higgs boson at the LHC; for a range of parameters the model considered has new physics at the TeV scale that is invisible, in the first few hundred inverse femtobarns of integrated luminosity at the LHC, except indirectly through the measurement of Higgs boson properties.
We demonstrate that amplitudes describing scattering of longitudinally polarized massive vector bosons present in non-Abelian Lee-Wick gauge theory do not grow with energy and, hence, satisfy the constraints imposed by perturbative unitarity. This re
sult contrasts with the widely-known violation of perturbative unitarity in the standard model with a very heavy Higgs. Our conclusions are valid to all orders of perturbation theory and depend on the existence of a formulation of the theory in which all operators are of dimension four or less. This can be thought of as a restriction on the kinds of higher dimension operator which can be included in the higher derivative formulation of the theory.
Recently an extension of the standard model (the Lee-Wick standard model) based on ideas of Lee and Wick (LW) was introduced. It does not contain quadratic divergences in the Higgs mass and hence solves the hierarchy puzzle. The LW-standard model con
tains new heavy LW-resonances at the TeV scale that decay to ordinary particles. In this paper we examine in more detail the flavor structure of the theory. We integrate out the heavy LW-fermions at tree level and find that this induces flavor changing Z boson couplings. However, these flavor changing neutral currents are acceptably small since they are automatically suppressed by small Yukawa couplings. This is the case even though the theory does not satisfy the principle of minimal flavor violation. New couplings of the charged W bosons to quarks and leptons are also induced. We also integrate out the LW-Higgs and examine the four-fermion operators induced.
