arXiv subjects

Duane A. Dicus

Publications and source records attributed to Duane A. Dicus.

At least 55 records · Page 3Linked to original sources

arXiv2001

Neutrino-Lepton Masses, Zee Scalars and Muon g-2

Evidence for neutrino oscillations is pointing to the existence of tiny but finite neutrino masses. Such masses may be naturally generated via radiative corrections in models such as the Zee model where a singlet Zee-scalar plays a key role. We minimally extend the Zee model by including a right-handed singlet neutrino ν_R. The radiative Zee-mechanism can be protected by a simple U(1)_X symmetry involving only the ν_R and a Zee-scalar. We further construct a class of models with a single horizontal U(1)_FN (a la Frogatt-Nielsen) such that the mass patterns of the neutrinos and leptons are naturally explained. We then analyze the muon anomalous magnetic moment (g-2) and the flavor changing μ--> eγdecay. The ν_R interaction in our minimal extension is found to induce the BNL g-2 anomaly, with a light charged Zee-scalar of mass 100-300 GeV.

hep-ph↗

arXiv2001

Ultrahigh-Energy Neutrino-Nucleon Cross Sections and Perturbative Unitarity

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 {\em 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 $E_ν\simeq 10^8 {\rm GeV}$. 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.

hep-ph↗

arXiv2000

The Drell-Hearn Sum Rule at Order Alpha**3

The Drell-Hearn-Gerasimov-Iddings (DHGI) sum rule for electrons is evaluated at order $α^3$ and shown to agree with the Schwinger contribution to the anomalous magnetic moment.

hep-ph↗

arXiv2000

Measuring the neutrino mass using intense photon and neutrino beams

We compute the cross section for neutrino-photon scattering taking into account a neutrino mass. We explore the possibility of using intense neutrino beams, such as those available at proposed muon colliders, together with high powered lasers to probe the neutrino mass in photon-neutrino collisions.

hep-ph↗

arXiv2000

Plasma Energy Loss into Kaluza-Klein Modes

Recently, Barger {\em et al.} computed energy losses into Kaluza Klein modes from astrophysical plasmas in the approximation of zero density for the plasmas. We extend their work by considering the effects of finite density for two plasmon processes. Our results show that, for fixed temperature, the energy loss rate per cm$^3$ is constant up to some critical density and then falls exponentially. This is true for transverse and longitudinal plasmons in both the direct and crossed channels over a wide range of temperature and density. A difficulty in deriving the appropriate covariant interaction energy at finite density and temperature is addressed. We find that, for the cases considered by Barger {\em et al.}, the zero density approximation and the neglect of other plasmon processes is justified to better than an order of magnitude.

hep-ph↗

arXiv2000

Photons, neutrinos and large compact space dimensions

We compute the contribution of Kaluza-Klein graviton exchange to the cross section for photon-neutrino scattering. Unlike the usual situation where the virtual graviton exchange represents a small correction to a leading order electroweak or strong amplitude, in this case the graviton contribution is of the same order as the electroweak amplitude, or somewhat larger. Inclusion of the graviton contribution is not sufficient to allow high energy neutrinos to scatter from relic neutrinos in processes such as $ν\barν\toγγ$, but the photon-neutrino decoupling temperature is substantially reduced.

hep-ph↗

arXiv1999

Radiative corrections to the decays K_L^0->e^+e^- and K_L^0->mu^+mu^-

We calculate the rates and lepton (l) invariant mass distributions for decays of the form 0^{-+}->l^+l^-γ, which are important radiative corrections to the purely leptonic decays 0^{-+}->l^+l^-. Our approach uses the loop diagrams which arise by including the two photon intermediate state and we retain the imaginary parts of the loops - a radiative extension of the `unitarity bound' for the process. These results are compared which those obtained using a model in which the meson couples directly to the leptons.

hep-ph↗

arXiv1998

High energy photon-neutrino interactions

A general decomposition of the amplitudes for the $2\to 2$ processes $γν\toγν$ and $γγ\toν\barν$ is obtained using gauge invariance and Bose symmetry. The restrictions implied by this decomposition are investigated for the reaction $γγ\toν\barν$ by computing the one-loop helicity amplitudes in the standard model. In the center of mass, where $\sqrt{s} = 2ω$, the cross section grows roughly as $ω^6$ up to the threshold for $W$-boson production, $\sqrt{s} = 2m_W$. Astrophysical implications of very high energy photon-neutrino interactions are discussed.

hep-ph↗

arXiv1998

gamma nu -> gamma gamma nu and crossed processes at energies below m_W

The cross sections for the processes $γν\to γγν$, $γγ\toγν\barν$ and $ν\barν\toγγγ$ are calculated for a range of center of mass energies from below $m_e$ to considerably above $m_e$, but much less than $m_W$. This enables us to treat the neutrino--electron coupling as a four--Fermi interaction and results in amplitudes which are electron box diagrams with three real photons and one virtual photon at their vertices. These calculations extend our previous low--energy effective interaction results to higher energies and enable us to determine where the effective theory is reliable.

hep-ph↗

arXiv1998

Collider Production of Spin 3/2 Particles

We consider the production of spin 3/2 quarks in hadron-hadron and photon-photon colliders. The cross sections at LHC energy is large enough to observe such exotic quarks up to a mass of a few TeV.

hep-ph↗

arXiv1998

Multilepton signatures of gauge mediated SUSY breaking at LEPII

In the framework of gauge-mediated supersymmetry breaking models pair production of the lightest neutralinos, scalar leptons, or charginos at LEPII gives rise to interesting signals involving multilepton final states and missing energy. In the parameter space where the scalar tau, $\tildeτ_1$, is the next-to-lightest supersymmetric particle, we identify three interesting regions, which give rise to distinctly different final states: (i) 2 $τ$-leptons plus missing energy, (ii) 4 charged leptons plus missing energy where in some regions all four are $τ$-leptons, or (iii) six charged leptons, of which four are $τ$-leptons and the other two are electrons or muons, plus missing energy. We study in detail the size of these regions in the parameter space of gauge-mediated models and give cross section contours in these regions for various LEPII energies. We also discuss the possibility of chargino-pair production at LEPII.

hep-ph↗

arXiv1998

Impact on SUSY-Breaking Models of the $R$-Parity Violating Squark Interpretation of the HERA Anomaly

The explanation of a 200 GeV R-parity violating squark to the HERA high-$Q^2$ anomaly would have an important impact on supersymmetry-breaking models. Here we show that a squark of mass around 200 GeV is disallowed in the minimal gauge-mediated SUSY-breaking models in the parameter space constrained by the radiative electroweak-symmetry breaking and the experimental lower limits on supersymmetric particles, even after including the large R-parity violating couplings. Supergravity motivated models can, on the other hand, give rise to these scalar quarks in a wide range of parameter space.

hep-ph↗

arXiv1998

Signatures for the Charged Higgs Decay of the Top Quark at the Tevatron

We investigate the effect that a charged Higgs decay channel for the top quark has on the signature for top quark pair production at the Tevatron. The branching ratios for the various multijet and multilepton final states arising from top pair production are obtained for a wide range of values for tangent beta and the charged Higgs boson mass. In addition, the effect of the charged Higgs decay of the top quark on the 2 b-tagged jets and 1 lepton channel is considered.

hep-ph↗

arXiv1998

Effective Lagrangians and low energy photon-photon scattering

We use the behavior of the photon-photon scattering for photon energies $ω$ less than the electron mass, $m_e$, to examine the implications of treating the Euler-Heisenberg Lagrangian as an effective field theory. Specifically, we determine the $ω^2/m_e^2$ behavior of the scattering amplitude predicted by including one-loop corrections to the Euler-Heisenberg effective Lagrangian together with the counterterms required by renomalizability. This behavior is compared with the energy dependence obtained by expanding the exact QED photon-photon scattering amplitude. If the introduction of counterterms in the effective field theory is restricted to those determined by renormalizability, the $ω^2/m_e^2$ dependences of the two expansions differ.

hep-ph↗

arXiv1997

Probing Anomalous Higgs Coupling through mu+ mu- --> H gamma

The process mu+ mu- --> H gamma, though small compared to the resonance process, could be observable at proposed muon colliders, given expected integrated luminosities. The apparently leading diagrams occur at tree-level, and are proportional to the Higgs-muon coupling. We show, however, that the one-loop contribution is comparable to the tree-level amplitude. Furthermore, the one-loop diagrams, unlike those at tree-level, could be greatly enhanced by possible anomalous Higgs-top quark or Higgs-gauge boson couplings. For a 500 GeV unpolarized muon collider, the total cross section for H-gamma associated production approaches 0.1 fb.

hep-ph↗

arXiv1997

Supernova Constraints on a Superlight Gravitino

In supergravity models with low supersymmetry breaking scale the gravitinos can be superlight with mass in the micro-eV to keV range. In such a case, gravitino emission provides a new cooling mechanism for protoneutron stars and therefore can provide constraints on the mass of the superlight gravitino. This happens because the coupling to matter of superlight gravitinos is dominated by its goldstino component, whose coupling to matter is inversely proportional to the scale of supersymmetry breaking and increases as the gravitino mass decreases. Present observations therefore provide lower limits on the gravitino mass. Using recently revised goldstino couplings, we find that the two dominant processes in supernova cooling are $e^+e^-\to \tilde{G}\tilde{G}$ and $γ+e^-\to e^-\tilde{G}\tilde{G}$. They lead to lower limits on the supersymmetry breaking scale $Λ_{S}$ from 160 to 500 GeV for core temperatures 30 to 60 MeV and electron chemical potentials 200 to 300 MeV. The corresponding lower limits on the gravitino mass are $.6 - 6\times 10^{-6}$ eV.

hep-ph↗

arXiv1997

Photon-neutrino interactions

The cross sections for the processes γν--> γγν, γγ-->γν\barν and ν\barν -->γγγare calculated with the aid of an effective Lagrangian derived from the Standard model. These cross sections are shown to be much larger than the elastic cross section σ(γν--> γν) for photon energies $ω> 1$ keV. Possible astrophysical implications are discussed.

hep-ph↗

arXiv1996

New Collider Bound on Light Gravitino Mass

In supergravity theories with a very light gravitino, the gluino decays dominantly to a gluon and a gravitino. This results in a much larger missing $E_T$ for the multijet final states in hadronic colliders. We use the latest Tevatron data for the multijet final states to set a new absolute lower bound of 3.0 x 10^{-13} GeV for the light gravitino mass.

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