Mitchell Golden

Multi-jet physics at hadron colliders

Abstract We discuss four-jet and six-jet events at the SSC, LHC and Tevatron. First, the QCD backgrounds to non-standard physics are presented. Then we investigate multi-jet signals for hadronically-decaying color-octet pseudoscalars and color-sextet or octet fermions. Finally, the discovery potential of each collider is estimated.

On the Hilbert space of the heavy quark effective theory

Abstract We give a careful description of the Hilbert space of the heavy quark effective theory. States must carry both velocity and momentum labels. We show that this formulation is necessary to resolve a paradox which arises in the effective theory when considering the matrix element of a light quark current between heavy meson states.

Hiding the electroweak symmetry breaking sector

Abstract It is generally assumed that in elastic W and Z scattering either there will be resonances with masses of less than 1 TeV (as expected, for example, in the weakly coupled one-doublet Higgs model) or the scattering amplitudes will be enhanced, indicating the presence of new strong interactions at or above 1 TeV. In this paper we note that there is another possibility: the electroweak symmetry breaking sector may be strongly coupled at low energies because of the presence of large numbers of particles other than the longitudinal components of the W and Z. In this case the elastic W and Z scattering amplitudes may be small without the appearance of any discernible resonances, while the total scattering cross sections are large. In such a model, at no energy is the number of WW or ZZ events large; discovering the electroweak symmetry breaking sector depends on the observation of other particles and our ability to associate them with symmetry breaking. We illustrate this possibility in the context of an O( N ) linear sigma model solved in the large- N limit.

Analyticity, crossing symmetry and the limits of chiral perturbation theory

The chiral Lagrangian for Goldstone-boson scattering is a power-series expansion in numbers of derivatives. Each successive term is suppressed by powers of a scale, Λ χ , which must be less than of order 4πf/√N where f is the Goldstone-boson decay constant and N is the number of flavors. The chiral expansion therefore breaks down at or below 4πf/√N. Because of crossing symmetry, some «isospin» channels will deviate from their low-energy behavior well before they approach the scale at which their low-energy amplitudes would violate unitarity. The breakdown of the chiral expansion is associated with the appearance of physical states other than Goldstone bosons

Electroweak corrections in technicolor reconsidered

Abstract Radiative corrections to electroweak parameters in technicolor theories may be evaluated by one of two techniques: either one estimates spectral function integrals using scaled QCD data, or one uses naive dimensional analysis with a chiral lagrangian. The former yields corrections to electroweak parameters proportional to the number of flavors and the number of colors, while the latter is proportional to the number of flavors squared and is independent of the number of colors. We attempt to resolve this apparent contradiction by showing that the spectrum of technicolor one obtains by scaling QCD data to high energies is unlikely to resemble that of an actual technicolor theory. The resonances are likely to be much lighter than naively supposed and the radiative corrections to electroweak parameters may by much larger. We also argue that much less is known about the spectrum and the radiative corrections in technicolor than was previously believed.

Six-jet signals of highly colored fermions

Abstract We discuss detection at the LHC and the SSC of hadronically-decaying heavy fermions belonging to higher representations of SU (3)color.

Heavy meson decay constants. 1/m corrections

Abstract The coefficients of the 1 m -suppressed dimension-five operators in the static effective field theory lagrangian have been calculated to one loop order. In this paper we calculate to order α s the coefficients of the 1 m -suppressed operators in the expansion of the vector and axial vector currents containing one light and one heavy quark field. The matrix element of the time component of the axial vector current determines the decay constants of pseudoscalar heavy-light mesons.

Unitarity and fermion mass generation

Abstract Some years ago Appelquist and Chanowitz considered the scattering of fermion-anti-fermion into a pair of longitudinal gauge bosons. Their calculation established that unitarity implies that the physics giving mass to a quark of mass m f must be below a mass scale of 16 πν 2 / m f ( ν = 246 GeV). This bound is a bit difficult to interpret, because the unitarity of gauge boson scattering requires in any case that there be new physics, such as a Higgs boson, with a mass lighter than this. This paper re-examines the Appelquist-Chanowitz bound in order to clarify its meaning. This work uses toy models with a singlet Higgs boson to unitarize gauge boson scattering, and considers other possibilities for the new physics affecting the fermion mass. This new physics has the effect of changing the Higgs boson-fermion-anti-fermion coupling. New physics cannot significantly alter this coupling unless it is substantially lighter than the Appelquist-Chanowitz bound.

Colored pseudo Goldstone bosons and gauge boson pairs.

If the electroweak symmetry breaking sector contains colored particles weighing a few hundred GeV, then they will be copiously produced at a hadron supercollider. Colored technipions can rescatter into pairs of gauge bosons. As proposed by Bagger, Dawson, and Valencia, this leads to gauge boson pair rates far larger than in the standard model. In this Letter we reconsider this mechanism, and illustrate it in a model in which the rates can be reliably calculated. The observation of both an enhanced rate of gauge-boson-pair events and colored particles would be a signal that the colored particles were pseudo Goldstone bosons of symmetry breaking.

Scalar resonances in Goldstone boson scattering

Abstract Recently it has been suggested that when both spontaneous and explicit chiral symmetry breaking occurs in models with a large number of Goldstone bosons there is a stable scalar resonance which can be interpreted as a bound state of pions. We discuss this proposal in the context of the O( n ) linear sigma models and examine the conditions under which such a resonance can occur. We find that there are three possible situations. There may be a stable bound state, there may be a broad resonance, or the pion-pion scattering amplitudes may behave as though there were a light scale present without there being a physical particle corresponding to it. In addition, we find that if the theory is very strongly coupled, the tachyon that afflicts this model moves to positive mass-squared, becoming a physical particle.