Richard J. Hill

Universal behavior in the scattering of heavy, weakly interacting dark matter on nuclear targets

Abstract Particles that are heavy compared to the electroweak scale ( M ≫ m W ), and that are charged under electroweak SU ( 2 ) gauge interactions display universal properties such as a characteristic fine structure in the mass spectrum induced by electroweak symmetry breaking, and an approximately universal cross section for scattering on nuclear targets. The heavy particle effective theory framework is developed to compute these properties. As illustration, the spin independent cross section for low-velocity scattering on a nucleon is evaluated in the limit M ≫ m W , including complete leading-order matching onto quark and gluon operators, renormalization analysis, and systematic treatment of perturbative and hadronic-input uncertainties.

Standard Model anatomy of WIMP dark matter direct detection II: QCD analysis and hadronic matrix elements

Models of weakly interacting massive particles (WIMPs) specified at the electroweak scale are systematically matched to effective theories at hadronic scales where WIMP-nucleus scattering observables are evaluated. Anomalous dimensions and heavy-quark threshold matching conditions are computed for the complete basis of lowest-dimension effective operators involving quarks and gluons. The resulting QCD renormalization group evolution equations are solved. The status of relevant hadronic matrix elements is reviewed and phenomenological illustrations are given, including details for the computation of the universal limit of nucleon scattering with heavy S U ( 2 ) W × U ( 1 ) Y charged WIMPs. Several cases of previously underestimated hadronic uncertainties are isolated. The results connect arbitrary models specified at the electroweak scale to a basis of n f = 3 -flavor QCD operators. The complete basis of operators and Lorentz invariance constraints through order v 2 / c 2 in the nonrelativistic nucleon effective theory are derived.

T-parity violation by anomalies

Little Higgs theories often rely on an internal parity (T-parity) to suppress nonstandard electroweak effects or to provide a dark matter candidate. We show that such a symmetry is generally broken by anomalies, as described by the Wess-Zumino-Witten term. We study a simple SU(3)xSU(3)/SU(3) Little Higgs scheme where we obtain a minimal form for the topological interactions of a single Higgs field. The results apply to more general models, including [SU(3)xSU(3)/SU(3)]{sup 4}, SU(5)/SO(5), and SU(6)/Sp(6)

Anomaly mediated neutrino-photon interactions at finite baryon density.

We propose new physical processes based on the axial vector anomaly and described by the Wess-Zumino-Witten term that couples the photon, Z-boson, and the omega-meson. The interaction takes the form of a pseudo-Chern-Simons term, approximately E(munurhosigma)omega(mu)ZnuFrhosigma. This term induces neutrino-photon interactions at finite baryon density via the coupling of the Z-boson to neutrinos. These interactions may be detectable in various laboratory and astrophysical arenas. The new interactions may account for the excess observed at the Fermilab Booster Neutrino Experiment MiniBooNE. They also produce a competitive contribution to neutron star cooling at temperatures greater, similar10(9) K. These processes and related axion-photon interactions at finite baryon density appear to be relevant in many astrophysical regimes.

Model independent analysis of proton structure for hydrogenic bound states

Proton structure effects in hydrogenic bound states are analyzed using nonrelativistic QED effective field theory. Implications for the Lamb shift in muonic hydrogen are discussed. Model-dependent assumptions in previous analyses are isolated, and sensitivity to poorly constrained hadronic structure in the two-photon exchange contribution is identified.

Model independent extraction of the proton charge radius from electron scattering

We combine constraints from analyticity with experimental electron-proton scattering data to determine the proton magnetic radius without model-dependent assumptions on the shape of the form factor. We also study the impact of including electron-neutron scattering data, and ππ → NN̄ data. Using representative datasets we find for a cut of Q2 ≤ 0.5 GeV2, r M = 0.91 +0.03 −0.06 ± 0.02 fm using just proton scattering data; r p M = 0.87 −0.05 ± 0.01 fm adding neutron data; and r p M = 0.87 +0.02 −0.02 fm adding ππ data. We also extract the neutron magnetic radius from these data sets obtaining rn M = 0.89 +0.03 −0.03 fm from the combined proton, neutron, and ππ data. ar X iv :1 40 7. 56 83 v1 [ he pph ] 2 1 Ju l 2 01 4

Weakly interacting stable hidden sector pions

An unbroken discrete symmetry, analogous to G-parity in QCD, exists in standard model extensions with vector-like coupling of electroweak SU(2) to “hidden sector” fermions that are confined by a strong gauge force. For an arbitrary irreducible SU(2) representation of the hidden sector fermions, the lightest hidden sector states form an isotriplet of “pions” with calculable mass splittings and couplings to standard model fields. The parity can be extended to fermions in real representations of color SU(3), and can provide dark matter candidates with distinct collider signatures.

Topological Physics of Little Higgs Bosons

Topological interactions will generally occur in composite Higgs or Little Higgs theories, extra-dimensional gauge theories in which A5 plays the role of a Higgs boson, and among the pNGBs of technicolor. This phenomena arises from the chiral and anomaly structure of the underlying UV completion theory, and/or through chiral delocalization in higher dimensions. These effects are described by a full Wess-Zumino-Witten term involving gauge fields and pNGBs. We give a general discussion of these interactions, some of which may have novel signatures at future colliders, such as the LHC and ILC.

Standard model gauging of the Wess-Zumino-Witten term: Anomalies, global currents, and pseudo-Chern-Simons interactions

The standard model SU(2){sub L}xU(1){sub Y} gauging of the Wess-Zumino-Witten term requires a modified counterterm when background fields, needed to generate the full set of currents, are introduced. The modified counterterm plays an essential role in properly defining covariant global currents and their anomalies. For example, it is required in order to correctly derive the gauge-invariant baryon number current and its anomalous divergence. The background fields can also be promoted to a description of the physical spin-1 vector and axial-vector mesons in QCD and the counterterm leads to novel interactions. These are (pseudo)Chern-Simons terms, such as {epsilon}{sup {mu}}{sup {nu}}{sup {rho}}{sup {sigma}}{omega}{sub {mu}}Z{sub {nu}}{partial_derivative}{sub {rho}}A{sub {sigma}} and {epsilon}{sup {mu}}{sup {nu}}{sup {rho}}{sup {sigma}}{rho}{sub {mu}}{sup {+-}}W{sub {nu}}{sup {+-}}{partial_derivative}{sub {rho}}A{sub {sigma}} that mediate new interactions between neutrinos and photons at finite baryon density.

Extraction of the proton radius from electron-proton scattering data

We perform a new analysis of electron-proton scattering data to determine the proton electric and magnetic radii, enforcing model-independent constraints from form factor analyticity. A wideranging study of possible systematic eects is performed. An improved analysis is developed that rebins data taken at identical kinematic settings, and avoids a scaling assumption of systematic errors with statistical errors. Employing standard models for radiative corrections, our improved analysis of the 2010 Mainz A1 Collaboration data yields a proton electric radius rE = 0:895(20) fm and magnetic radius rM = 0:776(38) fm. A similar analysis applied to world data (excluding Mainz data) implies rE = 0:916(24) fm and rM = 0:914(35) fm. The Mainz and world values of the charge radius are consistent, and a simple combination yields a value rE = 0:904(15) fm that is 4 larger than the CREMA Collaboration muonic hydrogen determination. The Mainz and world values of the magnetic radius dier