arXiv subjects
Publications and source records attributed to Paul Langacker.
The implications of the deficit of solar neutrinos are discussed. If all of the experiments are taken literally the relative suppressions render an astrophysical explanation unlikely. Allowing MSW conversions, the data simultaneously determine the temperature of the core of the sun to within five percent. The implications of the atmospheric $ν_μ/ν_e$ ratio are briefly discussed.
The status of proton decay is described, including general motivations for baryon number violation, and the present and future experimental situation. Grand unification with and without supersymmetry is considered, including possible evidence from coupling constant unification and implications for proton decay and neutrino mass.
The status of coupling constant unification in the standard model and its supersymmetric extension are discussed. Uncertainties associated with the input coupling constants, $m_{t}$, threshold corrections at the low and high scales, and possible nonrenormalizable operators are parametrized and estimated. A simple parametrization of a general supersymmetric new particle spectrum is given. It is shown that an effective scale $M_{SUSY}$ can be defined, but for a realistic spectrum it may differ considerably from the typical new particle masses. The implications of the lower (higher) values of $α_{s}(M_{Z})$ suggested by low-energy ($Z$-pole) experiments are discussed.
We discuss three promising diagnostic probes of the couplings of a possible heavy $Z'$ boson at hadron colliders: the forward-backward asymmetry into leptons, the rare decay $Z' \ra W^{\pm} \ell^{\mp} ν$, and associated production $pp \ra Z'W,\; Z'Z$. A general model-independent framework is proposed for interpreting these and other data. Clean tests of whether a new $W'$ couples to right-handed currents, of the ratio $g_R/g_L$ of gauge couplings, and of the non-abelian vertex in left-right symmetric models are described.
We point out that the production cross section of $pp\to V'V$, with $V'=W',Z'$ and $V=W,Z$ is a useful diagnostic of $V'$ gauge couplings at future hadron colliders. For $M_{Z'}\simeq1$ TeV it would allow determination of combinations of $Z'$ gauge couplings to the quarks to around 10 percent. An analysis of the extraction of gauge couplings from the complementary tests: forward-backward asymmetry, rare decays $pp\to V'\to f_1{\bar f_2}V$, and the production cross section $pp\to V'V$ is given in a model-independent framework. Four ratios of charges are needed to characterize a general gauge theory with an additional family-independent $U_1'$ factor. We show that there are four functions of these ratios observable at hadron colliders, but for projected SSC and LHC luminosities only two combinations can be extracted. These yield a significant discrimination between interesting GUT-motivated models. Clean tests of whether a new $W'$ couples to right-handed currents, of the ratio $g_R/g_L$ of gauge couplings, and of the non-abelian vertex in left-right symmetric models are described.
The XXVII$^{\rm th}$ Rencontres de Moriond featured approximately 84 talks on a wide range of topics. I will try to summarize the highlights under the hypothesis that $SU_3 \x SU_2 \x U_1$ is correct to first approximation, concentrating on probes for new physics at various scales.
With the standard electroweak interactions, the lowest-order coherent forward scattering amplitudes of neutrinos in a CP symmetric medium (such as the early universe) are zero, and the index of refraction of a propagating neutrino can only arise from the expansion of gauge boson propagators, from radiative corrections, and from new physics interactions. Motivated by nucleosynthesis constraints on a possible sterile neutrino (suggested by the solar neutrino deficit and a possible $17\ keV$ neutrino), we calculate the standard model contributions to the neutrino index of refraction in the early universe, focusing on the period when the temperature was of the order of a few $MeV$. We find sizable radiative corrections to the tree level result obtained by the expansion of the gauge boson propagator. For $ν_e+e(\bar{e})\to ν_e+e(\bar{e})$ the leading log correction is about $+10\%$, while for $ν_e+ν_e(\barν_e)\to ν_e+ν_e(\barν_e)$ the correction is about $+20\%$. Depending on the family mixing (if any), effects from different family scattering can be dominated by radiative corrections. The result for $ν+γ\toν+γ$ is zero at one-loop level, even if neutrinos are massive. The cancellation of infrared divergence in a coherent process is also discussed.
We investigate the possibility of accommodating neutrino masses compatible with the MSW study of the Solar neutrino deficit within the minimal supersymmetric Standard Model. The ``gravity-induced'' seesaw mechanism based on an interplay of nonrenormalizable and renormalizable terms in the superpotential allows neutrino masses $m_ν\propto m_u^2/M_I$, with $m_u$ the corresponding quark mass and $M_I\simeq 4\times10^{11}$ GeV, while at the same time ensuring the grand desert with the gauge coupling unification at $M_U\simeq 2\times10^{16}$ GeV. The proposed scenario may be realized in a class of string vacua, {\it i.e.,} large radius ($R^2/α'={\cal O}(20)$) $(0,2)$ Calabi-Yau spaces. In this case $M_U^2=M_C^2/{\cal O} (2R^2/α')$ and $M_I= {\cal O}(e^{-R^2/α'})M_C$. Here $M_C=g\times 5.2\times 10^{17}$GeV is the scale of the tree level (genus zero) gauge coupling ($g$) unification.