Relaxation mechanisms: From Damour-Polyakov to Peccei-Quinn

The ralaxation mechanism of Damour-Polyakov for fixing the vacuum expectation value of certain scalar fields (moduli) in string theory could provide a convenient framework for the Peccei-Quinn relaxation mechanism and remove the narrow "axion window".Comment: 9 pages, late

Dimension-six top-Higgs interaction and its effect in collider phenomenology

Measurement of the Yukawa interaction between the top quark and the Higgs boson should be useful to clarify the mechanism of fermion mass generation. We discuss the impact of non-standard interactions characterized by dimension-six operators on the effective top Yukawa coupling. The cross section of the process $e^-e^+ \to W^-W^+ \nu \bar \nu \to t \bar t \nu \bar \nu$ is calculated including these operators, and possible deviation from the standard model prediction is evaluated under the constraint from perturbative unitarity and current experimental data. We find that if the new physics scale is in a TeV region, the cross section can be significantly enhanced due to the non-standard interactions. Such a large effect should be detectable at the International Linear Collider.Comment: 22 pages, RevTex4, 20 eps figure

Breit-Wigner formalism for non-Abelian theories

The consistent description of resonant transition amplitudes within the framework of perturbative field theories necessitates the definition and resummation of off-shell Green's functions, which must respect several crucial physical requirements. In particular, the generalization of the usual Breit-Wigner formalism in a non-Abelian context constitutes a highly non-trivial problem, related to the fact that the conventionally defined Green's functions are unphysical. We briefly review the main field-theoretical difficulties arising when attempting to use such Green's functions outside the confines of a fixed order perturbative calculation, and explain how this task has been successfully accomplished in the framework of the pinch technique

p p -> j j e+/- mu+/- nu nu and j j e+/- mu-/+ nu nu at O(\alpha_{em}^6) and O(\alpha_{em}^4 \alpha_s^2) for the Study of the Quartic Electroweak Gauge Boson Vertex at LHC

We analyze the potential of the CERN Large Hadron Collider (LHC) to study the structure of quartic vector-boson interactions through the pair production of electroweak gauge bosons via weak boson fusion q q -> q q W W. In order to study these couplings we have performed a partonic level calculation of all processes p p -> j j e+/- mu+/- nu nu and pp -> j j e+/- mu-/+ nu nu at the LHC using the exact matrix elements at O(\alpha_{em}^6) and O(\alpha_{em}^4 \alpha_s^2) as well as a full simulation of the t tbar plus 0 to 2 jets backgrounds. A complete calculation of the scattering amplitudes is necessary not only for a correct description of the process but also to preserve all correlations between the final state particles which can be used to enhance the signal. Our analyses indicate that the LHC can improve by more than one order of magnitude the bounds arising at present from indirect measurements.Comment: 26 pages, 8 figures, revised version with some typos corrected, and some comments and references adde

Anomalous gauge couplings of the Higgs boson at high energy photon colliders

We study the sensitivity of testing the anomalous gauge couplings $g_{HVV}$'s of the Higgs boson in the formulation of linearly realized gauge symmetry via the processes $\gamma\gamma\to ZZ$ and $\gamma\gamma\to WWWW$ at polarized and unpolarized photon colliders based on $e^+e^-$ linear colliders of c.m.~energies 500 GeV, 1 TeV, and 3 TeV. Signals beyond the standard model (SM) and SM backgrounds are carefully studied. We propose certain kinematic cuts to suppress the standard model backgrounds. For an integrated luminosity of 1 ab$^{-1}$, we show that (a) $\gamma\gamma\to ZZ$ can provide a test of $g_{H\gamma\gamma}$ to the $3\sigma$ sensitivity of $O(10^{-3}-10^{-2})$ TeV$^{-1}$ at a 500 GeV ILC, and $O(10^{-3})$ TeV$^{-1}$ at a 1 TeV ILC and a 3 TeV CLIC, and (b) $\gamma\gamma\to WWWW$ at a 3 TeV CLIC can test all the anomalous couplings $g_{HVV}$'s to the $3\sigma$ sensitivity of $O(10^{-3}-10^{-2})$ TeV$^{-1}$.Comment: 30 pages, 17 figure

Unitarity and Bounds on the Scale of Fermion Mass Generation

The scale of fermion mass generation can, as shown by Appelquist and Chanowitz, be bounded from above by relating it to the scale of unitarity violation in the helicity nonconserving amplitude for fermion-anti-fermion pairs to scatter into pairs of longitudinally polarized electroweak gauge bosons. In this paper, we examine the process t tbar -> W_L W_L in a family of phenomenologically-viable deconstructed Higgsless models and we show that scale of unitarity violation depends on the mass of the additional vector-like fermion states that occur in these theories (the states that are the deconstructed analogs of Kaluza-Klein partners of the ordinary fermions in a five-dimensional theory). For sufficiently light vector fermions, and for a deconstructed theory with sufficiently many lattice sites (that is, sufficiently close to the continuum limit), the Appelquist-Chanowitz bound can be substantially weakened. More precisely, we find that, as one varies the mass of the vector-like fermion for fixed top-quark and gauge-boson masses, the bound on the scale of top-quark mass generation interpolates smoothly between the Appelquist-Chanowitz bound and one that can, potentially, be much higher. In these theories, therefore, the bound on the scale of fermion mass generation is independent of the bound on the scale of gauge-boson mass generation. While our analysis focuses on deconstructed Higgsless models, any theory in which top-quark mass generation proceeds via the mixing of chiral and vector fermions will give similar results.Comment: 12 pages, 11 eps figures included, revtex. Refrences added; wording modified slightly to emphasize focus on top-quar

Factorization Structure of Gauge Theory Amplitudes and Application to Hard Scattering Processes at the LHC

Previous work on electroweak radiative corrections to high energy scattering using soft-collinear effective theory (SCET) has been extended to include external transverse and longitudinal gauge bosons and Higgs bosons. This allows one to compute radiative corrections to all parton-level hard scattering amplitudes in the standard model to NLL order, including QCD and electroweak radiative corrections, mass effects, and Higgs exchange corrections, if the high-scale matching, which is suppressed by two orders in the log counting, and contains no large logs, is known. The factorization structure of the effective theory places strong constraints on the form of gauge theory amplitudes at high energy for massless and massive gauge theories, which are discussed in detail in the paper. The radiative corrections can be written as the sum of process-independent one-particle collinear functions, and a universal soft function. We give plots for the radiative corrections to q qbar -> W_T W_T, Z_T Z_T, W_L W_L, and Z_L H, and gg -> W_T W_T to illustrate our results. The purely electroweak corrections are large, ranging from 12% at 500 GeV to 37% at 2 TeV for transverse W pair production, and increasing rapidly with energy. The estimated theoretical uncertainty to the partonic (hard) cross-section in most cases is below one percent, smaller than uncertainties in the parton distribution functions (PDFs). We discuss the relation between SCET and other factorization methods, and derive the Magnea-Sterman equations for the Sudakov form factor using SCET, for massless and massive gauge theories, and for light and heavy external particles.Comment: 44 pages, 30 figures. Refs added, typos fixed. ZL ZL plots removed because of a possible subtlet

Leptogenesis with "Fuzzy Mass Shell" for Majorana Neutrinos

We study the mixing of elementary and composite particles. In quantum field theory the mixing of composite particles originates in the couplings of the constituent quarks and for neutrinos in self-energy diagrams. In the event that the incoming and outgoing neutrinos have different masses, the self-energy diagrams vanish because energy is not conserved but the finite decaying widths make the mixing possible. We can consider the neutrinos to be "fuzzy" states on their mass shell and the mixing is understood as the overlap of two wavefunctions. These considerations restrict the mass difference to be approximately equal to or smaller than the largest of the two widths: abs(M_i - M_j) lessorequal max(Gamma_i, Gamma_j).Comment: 11 pages, 1 figur

Leptogenesis with Heavy Majorana Neutrinos Reexamined

The mass term for Majorana neutrinos explicitly violates lepton number. Several authors have used this fact to create a lepton asymmetry in the universe by considering CP violating effects in the one loop self-energy correction for the decaying heavy Majorana neutrino. We compare and comment on the different approaches used to calculate the lepton asymmetry including those using an effective Hamiltonian and resummed propagators. We also recalculate the asymmetry in the small mass difference limit.Comment: 16 pages, LaTex, 1 figure included. 2 footnotes and 1 reference adde

Universality-Breaking Effects in Leptonic Z Decays

We analyze the possibility of universality violation in diagonal leptonic decays of the $Z$ boson, in the context of interfamily "see-saw" models. In a minimal extension of the Standard Model with right-handed neutrino fields, we find that universality-breaking effects increase quadratically with the heavy Majorana neutrino mass and may be observed in the running $LEP$ experiments.Comment: MZ-TH/93-04 #, LaTeX, 14 p. (2 Figs