39321472
Size and scaling of the double-helicity-flip hadronic structure function.
Recently, Jaffe and Manohar identified a new leading-twist structure function {Delta}({ital x},{ital Q}{sup 2}), which can be measured in deep-inelastic scattering from polarized targets with spin {ge}1. We calculate the scaling behavior of {Delta}({ital x},{ital Q}{sup 2}) in QCD, both by computing the anomalous dimensions of the associated operators and by finding the splitting function for the appropriate parton density. We also estimate the size of the lowest moment of {Delta}({ital x},{ital Q}{sup 2}) in the bag model. In an appendix we give the complete cross section for electroproduction from a spin-1 target of arbitrary polarization.
6678978
Ultrahigh-energy neutrino–nucleon cross sections and perturbative unitarity
Abstract Unitarity relates the total cross section for neutrino–nucleon scattering to the neutrino–nucleon forward scattering amplitude. Assuming the validity of the perturbative expansion of the forward amplitude in the weak coupling constant, we derive a unitarity bound on the inelastic cross section. The inelastic cross section saturates this bound at a typical neutrino energy E ν ≃10 8  GeV. This implies that calculations of the inelastic cross section that use current parton distribution functions and lowest order weak perturbation theory are unreliable above this energy.
17090149
Higgsless electroweak symmetry breaking from theory space
We investigate unitarity of W+W− scattering in the context of theory space models of the form U(1) × [SU(2)]N × SU(2)N+1, which are broken down to U(1)EM by non-linear Σ fields, without the presence of a physical Higgs Boson. By allowing the couplings of the U(1) and the final SU(2)N+1 to vary, we can fit the W and Z masses, and we find that the coefficient of the term in the amplitude that grows as E2/mW2 at high energies is suppressed by a factor of (N+1)−2. In the N+1→∞ limit the model becomes a 5-dimensional SU(2) gauge theory defined on an interval, where boundary terms at the two ends of the interval break the SU(2) down to U(1)EM. These boundary terms also modify the Kaluza-Klein (KK) mass spectrum, so that the lightest KK states can be identified as the W and Z bosons. The T parameter, which measures custodial symmetry breaking, is naturally small in these models. Depending on how matter fields are included, the strongest experimental constraints come from precision electroweak limits on the S parameter.
17272111
Effects of fermion localization in Higgsless theories and electroweak constraints
Abstract Extra-dimensional Higgsless models with electroweak symmetry breaking through boundary conditions generically have difficulties with electroweak precision constraints, when the fermions are localized to the “branes” in the fifth dimension. In this Letter we show that these constraints can be relaxed by allowing the light fermions to have a finite extent into the bulk of the fifth dimension. The T and U electroweak parameters can be naturally suppressed by a custodial symmetry, while the S parameter can be made to vanish through a cancellation, if the leakage into the bulk of the light gauge fields and the light left-handed fermion fields are of the same size. This cancellation is possible while allowing realistic values for the first two generations of fermion masses, although special treatment is probably required for the top quark. We present this idea here in the context of a specific continuum theory-space model; however, it can be applied to any five-dimensional Higgsless model, either with a flat or a warped background.
118429632
Higgs Boson Cross Section from CTEQ-TEA Global Analysis
We study the uncertainties of the Higgs boson production cross section through the gluon fusion subprocess at the LHC (with $\sqrt s=7, 8$ and $14$ TeV) arising from the uncertainties of the parton distribution functions (PDFs) and of the value of the strong coupling constant $\alpha_s(M_Z)$. These uncertainties are computed by two complementary approaches, based on the Hessian and the Lagrange Multiplier methods within the CTEQ-TEA global analysis framework. We find that their predictions for the Higgs boson cross section are in good agreement. Furthermore, the result of the Lagrange Multiplier method supports the prescriptions we have previously provided for using the Hessian method to calculate the combined PDF and $\alpha_s$ uncertainties, and to estimate the uncertainties at the $68\%$ confidence level by scaling them from the $90\%$ confidence level.
17634589
Radiative electroweak symmetry breaking in a Little Higgs model
We present a new Little Higgs model, motivated by the deconstruction of a five-dimensional gauge-Higgs model. The approximate global symmetry is SO(5)0 × SO(5)1, breaking to SO(5), with a gauged subgroup of [SU(2)0L × U(1)0R] × O(4)1, breaking to SU(2)L ×U(1)Y . Radiative corrections produce an additional small vacuum misalignment, breaking the electroweak symmetry down to U(1)EM. Novel features of this model are: the only un-eaten pseudo-Goldstone boson in the effective theory is the Higgs boson; the model contains a custodial symmetry, which ensures that $ \widehat{T} = 0 $ at tree-level; and the potential for the Higgs boson is generated entirely through one-loop radiative corrections. A small negative mass-squared in the Higgs potential is obtained by a cancellation between the contribution of two heavy partners of the top quark, which is readily achieved over much of the parameter space. We can then obtain both a vacuum expectation value of v = 246 GeV and a light Higgs boson mass, which is strongly correlated with the masses of the two heavy top quark partners. For a scale of the global symmetry breaking of f = 1 TeV and using a single cutoff for the fermion loops, the Higgs boson mass satisfies 120 GeV ≲ MH ≲ 150 GeV over much of the range of parameter space. For f raised to 10 TeV, these values increase by about 40 GeV. Effects at the ultraviolet cutoff scale may also raise the predicted values of the Higgs boson mass, but the model still favors MH ≲ 200GeV.
44869344
Stability and Hamiltonian formulation of higher derivative theories.
We analyze the presumptions which lead to instabilities in theories of order higher than second. That type of fourth order gravity which leads to an inflationary (quasi de Sitter) period of cosmic evolution by inclusion of one curvature squared term (i.e. the Starobinsky model) is used as an example. The corresponding Hamiltonian formulation (which is necessary for deducing the Wheeler de Witt equation) is found both in the Ostrogradski approach and in another form. As an example, a closed form solution of the Wheeler de Witt equation for a spatially flat Friedmann model and L = R2 is found. The method proposed by Simon to bring fourth order gravity to second order can be (if suitably generalized) applied to bring sixth order gravity to second order. PACS numbers: 0320 Classical mechanics of discrete systems: general mathematical aspects; 9880 Cosmology; 0450 Other theories of gravitation
6752160
Bound-valence-quark contributions to hadron structure functions.
The conventional separation of valence''- and sea''-quark distributions of a hadron implicitly assumes that the quark and antiquark contributions to the sea are identical in shape, although this cannot be strictly correct due to the exclusion principle. A new separation of bound-valence''- and - non-valence''- quark distributions of a hadron is proposed which incorporates the Pauli principle and relates the valence component to the wave functions of the bound-state valence constituents. With this new definition, the non-valence-quark distributions correspond to structure functions which would be measured if the valence quarks of the target hadron were chargeless. The bound-valence-quark distributions are not singular at small {ital x}, thus allowing for the calculation of sum rules and expectation values which would otherwise be divergent.
18789561
Is the chiral angle related to the vacuum charge? A study in one dimension.
A resolution of ambiguities that arise in relating the chiral angle to the vacuum charge is presented; their relationship is studied and clarified. A recently developed formulation is applied to a simple one-dimensional example with fractional charge. This example provides a setting in which the breakdown of the adiabatic approximation and the winding of the chiral angle by multiples of 2\ensuremath{\pi} can be studied. We find that the above situations do not a priori imply a change in the vacuum charge nor any ambiguity in its definition. However, a mathematical and physical criterion for the occurrence of level crossing, leading to an integer change in the charge of the vacuum, is provided. The results are given and analyzed from a physical point of view and their generality is discussed.
7555577
Measurement of elastic electron-neutron scattering and inelastic electron-deuteron scattering cross sections at high momentum transfer.
We have measured inelastic electron-deuteron, electron-proton, and electron-aluminum cross sections at 10{degree} in the kinematic region between elastic deuteron scattering and the second resonance region at six beam energies between 9.8 and 21 GeV. The elastic electron-neutron cross section was extracted from the quasielastic data at {ital Q}{sup 2}=2.5, 4.0, 6.0, 8.0, and 10.0 (GeV/{ital c}){sup 2}. The ratio of elastic cross sections {sigma}{sub {ital n}}/{sigma}{sub {ital p}} falls with increasing {ital Q}{sup 2} above 6 (GeV/{ital c}){sup 2}. The inelastic data are compatible either with {ital y} scaling (scattering from a single nucleon) or with {xi} scaling (scattering from quarks).
31181088
Plane domain walls when coupled with the Brans-Dicke scalar field.
The space-times of plane thin domain walls are studied in the context of the Brans-Dicke (BD) theory of gravity by using distribution theory. In particular, the BD field equations are divided into two groups: one holding in the regions outside of the wall and the other holding on the wall. It is found that the equations on the wall take a very simple form, and are given explicitly in terms of the metric coefficients and the BD scalar field. As an application of the theory developed, a class of exact solutions, which represents a plane domain wall interacting with the BD scalar field, is given and studied. It is found that the surface energy density of the wall always exponentially decreases as the time develops; this is one possible solution of the domain wall problem in cosmological models founded on general relativity