We discuss how new physics not encompassed within the STU oblique correction framework can be con... more We discuss how new physics not encompassed within the STU oblique correction framework can be constrained from precision electroweak measurements via vertex corrections to Z-pole observables.
Strong Coupling Gauge Theories and Effective Field Theories - Proceedings of the 2002 International Workshop, 2003
The Z-pole data from e + e − colliders 1 and results from the NuTeV 2 experiment at Fermilab can ... more The Z-pole data from e + e − colliders 1 and results from the NuTeV 2 experiment at Fermilab can be brought into agreement if (1) the neutrino-Z couplings were suppressed relative to the Standard Model (SM), and (2) the Higgs boson were much heavier than suggested by SM global fits 1 . However, increasing the Higgs boson mass will move the theoretical value of the W mass away from its experimental value. A large and positive U parameter becomes necessary to account for the difference. We discuss what type of new physics may lead to such values of U .
Large critical dimensions in the diffusion equation
We study the evolution of a random initial field under pure diffusion in various space dimensions... more We study the evolution of a random initial field under pure diffusion in various space dimensions. From numerical calculations we find that the persistence properties of the system show sharp transitions at critical dimensions d1=26 and d2=46. Potential relevance of these results to the phase space dynamics of small molecules will also be discussed.
We consider a model with extra compact dimensions in which only gravity exists in the 4 + n dimen... more We consider a model with extra compact dimensions in which only gravity exists in the 4 + n dimensional bulk. If the gravitational connection is not assumed to be symmetric, that is, unless torsion is artificially set to zero, then a universal contact interaction among the fermions on the 4-dimensional wall is induced. Using a global fit to Z-pole observables, we find the 3σ bound on the scale of quantum gravity to be M S = 28 TeV for n = 2. If Dirac or light sterile neutrinos are present, the data from SN1987A increase the bound to √ nM S ≥ 210 TeV.
We study the evolution of a random initial field under pure diffusion in various space dimensions... more We study the evolution of a random initial field under pure diffusion in various space dimensions. From numerical calculations we find that the persistence properties of the system show sharp transitions at critical dimensions d1 ≃ 26 and d2 ≃ 46. We also give refined measurements of the persistence exponents for low dimensions.
We use Monte Carlo simulations to obtain an improved lattice measurement of the critical coupling... more We use Monte Carlo simulations to obtain an improved lattice measurement of the critical coupling constant λ/µ 2 crit for the continuum (1 + 1)-dimensional (λ/4)φ 4 theory. We find that the critical coupling constant depends logarithmically on the lattice coupling, resulting in a continuum value of λ/µ 2 crit = 10.8 +.10 −.05 , in considerable disagreement with the previously reported λ/µ 2 crit = 10.26 +.08 −.04 .
We consider extensions of the Standard Model with an extra U (1) gauge boson which couples to B -... more We consider extensions of the Standard Model with an extra U (1) gauge boson which couples to B -(αL e + βL µ + γL τ ) with α + β + γ = 3. We show that the extra gauge boson necessarily mixes with the Z, leading to potentially significant corrections to the Zf f vertex. The constraints on the size of this correction imposed by the Z-pole data from LEP and SLD are derived.
We discuss the choice of gauge field basis in multiple-U (1) gauge theories. We find that there i... more We discuss the choice of gauge field basis in multiple-U (1) gauge theories. We find that there is a preferred basis, specified by the charge orthogonality condition, in which the U (1) gauge fields do not mix under one-loop renormalization group running.
We use the LEP/SLD data to place constraints on Topcolor Assisted Technicolor Models. We find tha... more We use the LEP/SLD data to place constraints on Topcolor Assisted Technicolor Models. We find that due to a large negative shift in R b induced by charged top-pion exchange, it is difficult to make the models compatible with experiment.
We study constraints on type-II two Higgs doublet models at large tan β from LEP/SLD Z-pole data ... more We study constraints on type-II two Higgs doublet models at large tan β from LEP/SLD Z-pole data and from lepton universality violation in W decay. We perform a global fit and find that, in the context of Z decay, the LEP/SLD experimental values for lepton universality violation, R b , and A b all somewhat disfavor the model. Contributions from the neutral Higgs sector can be used to constrain the scalar-pseudoscalar Higgs mass splittings. Contributions from the charged Higgs sector allow us to constrain the charged Higgs mass. For tan β = 100 we obtain the 1σ classical (Bayesian) bounds of m H ± ≥ 670 GeV (370 GeV) and 1 ≥ m h 0 /m A 0 ≥ 0.68 (0.64).
Recent results from the NuTeV experiment at Fermilab and the deviation of the Z invisible width, ... more Recent results from the NuTeV experiment at Fermilab and the deviation of the Z invisible width, measured at LEP/SLC, from its Standard Model (SM) prediction suggest the suppression of neutrino-Z couplings. Such suppressions occur naturally in models which mix the neutrinos with heavy gauge singlet states. We postulate a universal suppression of the Zνν couplings by a factor of (1 − ε) and perform a fit to the Z-pole and NuTeV observables with ε and the oblique correction parameters S and T . Compared to a fit with S and T only, inclusion of ε leads to a dramatic improvement in the quality of the fit. The values of S and T preferred by the fit can be obtained within the SM by a simple increase in the Higgs boson mass. However, if the W mass is also included in the fit, a non-zero U parameter becomes necessary which cannot be supplied within the SM. The preferred value of ε suggests that the seesaw mechanism may not be the reason why neutrinos are so light.
In a recent paper, we pointed out that mixing of the light neutrinos with heavy gauge singlet sta... more In a recent paper, we pointed out that mixing of the light neutrinos with heavy gauge singlet states could reconcile the Z-pole data from e+e- colliders and the nu_mu (anti-nu_mu) scattering data from the NuTeV experiment at Fermilab. We further noted that the mixing angle required to fit the data is much larger than what would be expected from the conventional seesaw mechanism. In this paper, we show how such mixings can be arranged by a judicious choice of the neutrino mass texture. We also argue that by invoking the unification of the Dirac mass matrix for the up-type quarks and the neutrinos, the mass of the heavy states can naturally be expected to be in the few TeV range. The model is strongly constrained by the lepton flavor changing process mu -> e gamma which requires lepton universality to be violated in the charged channel.
We analyze the one loop corrections to hadronic Z decays in an R-parity violating extension to th... more We analyze the one loop corrections to hadronic Z decays in an R-parity violating extension to the Minimal Supersymmetric Standard Model (MSSM). Performing a global fit to all the hadronic observables at the Z-peak, we obtain stringent constraints on the R-violating coupling constants λ ′ and λ ′′ . The presence of these couplings worsens the agreement with the data relative to the Standard Model. The strongest constraints come from the b asymmetry parameters A b and A FB (b). From a classical statistical analysis we find that the couplings λ ′ i31 , λ ′ i32 , and λ ′′ 321 are ruled out at the 1σ level, and that λ ′ i33 and λ ′′ 33i are ruled out at the 2σ level. We also obtain Bayesian confidence limits for the R-violating couplings.
We review the current status of precision electroweak measurements and the constraints they impos... more We review the current status of precision electroweak measurements and the constraints they impose on new physics. We perform a model independent analysis using the STU-formalism of Ref. 1, and then discuss how the Z-pole data from LEP and SLD can be used to constrain models that are not covered within that framework.
We discuss how new physics not encompassed within the STU oblique correction framework can be con... more We discuss how new physics not encompassed within the STU oblique correction framework can be constrained from precision electroweak measurements via vertex corrections to Z-pole observables.
Strong Coupling Gauge Theories and Effective Field Theories - Proceedings of the 2002 International Workshop, 2003
The Z-pole data from e + e − colliders 1 and results from the NuTeV 2 experiment at Fermilab can ... more The Z-pole data from e + e − colliders 1 and results from the NuTeV 2 experiment at Fermilab can be brought into agreement if (1) the neutrino-Z couplings were suppressed relative to the Standard Model (SM), and (2) the Higgs boson were much heavier than suggested by SM global fits 1 . However, increasing the Higgs boson mass will move the theoretical value of the W mass away from its experimental value. A large and positive U parameter becomes necessary to account for the difference. We discuss what type of new physics may lead to such values of U .
Large critical dimensions in the diffusion equation
We study the evolution of a random initial field under pure diffusion in various space dimensions... more We study the evolution of a random initial field under pure diffusion in various space dimensions. From numerical calculations we find that the persistence properties of the system show sharp transitions at critical dimensions d1=26 and d2=46. Potential relevance of these results to the phase space dynamics of small molecules will also be discussed.
We consider a model with extra compact dimensions in which only gravity exists in the 4 + n dimen... more We consider a model with extra compact dimensions in which only gravity exists in the 4 + n dimensional bulk. If the gravitational connection is not assumed to be symmetric, that is, unless torsion is artificially set to zero, then a universal contact interaction among the fermions on the 4-dimensional wall is induced. Using a global fit to Z-pole observables, we find the 3σ bound on the scale of quantum gravity to be M S = 28 TeV for n = 2. If Dirac or light sterile neutrinos are present, the data from SN1987A increase the bound to √ nM S ≥ 210 TeV.
We study the evolution of a random initial field under pure diffusion in various space dimensions... more We study the evolution of a random initial field under pure diffusion in various space dimensions. From numerical calculations we find that the persistence properties of the system show sharp transitions at critical dimensions d1 ≃ 26 and d2 ≃ 46. We also give refined measurements of the persistence exponents for low dimensions.
We use Monte Carlo simulations to obtain an improved lattice measurement of the critical coupling... more We use Monte Carlo simulations to obtain an improved lattice measurement of the critical coupling constant λ/µ 2 crit for the continuum (1 + 1)-dimensional (λ/4)φ 4 theory. We find that the critical coupling constant depends logarithmically on the lattice coupling, resulting in a continuum value of λ/µ 2 crit = 10.8 +.10 −.05 , in considerable disagreement with the previously reported λ/µ 2 crit = 10.26 +.08 −.04 .
We consider extensions of the Standard Model with an extra U (1) gauge boson which couples to B -... more We consider extensions of the Standard Model with an extra U (1) gauge boson which couples to B -(αL e + βL µ + γL τ ) with α + β + γ = 3. We show that the extra gauge boson necessarily mixes with the Z, leading to potentially significant corrections to the Zf f vertex. The constraints on the size of this correction imposed by the Z-pole data from LEP and SLD are derived.
We discuss the choice of gauge field basis in multiple-U (1) gauge theories. We find that there i... more We discuss the choice of gauge field basis in multiple-U (1) gauge theories. We find that there is a preferred basis, specified by the charge orthogonality condition, in which the U (1) gauge fields do not mix under one-loop renormalization group running.
We use the LEP/SLD data to place constraints on Topcolor Assisted Technicolor Models. We find tha... more We use the LEP/SLD data to place constraints on Topcolor Assisted Technicolor Models. We find that due to a large negative shift in R b induced by charged top-pion exchange, it is difficult to make the models compatible with experiment.
We study constraints on type-II two Higgs doublet models at large tan β from LEP/SLD Z-pole data ... more We study constraints on type-II two Higgs doublet models at large tan β from LEP/SLD Z-pole data and from lepton universality violation in W decay. We perform a global fit and find that, in the context of Z decay, the LEP/SLD experimental values for lepton universality violation, R b , and A b all somewhat disfavor the model. Contributions from the neutral Higgs sector can be used to constrain the scalar-pseudoscalar Higgs mass splittings. Contributions from the charged Higgs sector allow us to constrain the charged Higgs mass. For tan β = 100 we obtain the 1σ classical (Bayesian) bounds of m H ± ≥ 670 GeV (370 GeV) and 1 ≥ m h 0 /m A 0 ≥ 0.68 (0.64).
Recent results from the NuTeV experiment at Fermilab and the deviation of the Z invisible width, ... more Recent results from the NuTeV experiment at Fermilab and the deviation of the Z invisible width, measured at LEP/SLC, from its Standard Model (SM) prediction suggest the suppression of neutrino-Z couplings. Such suppressions occur naturally in models which mix the neutrinos with heavy gauge singlet states. We postulate a universal suppression of the Zνν couplings by a factor of (1 − ε) and perform a fit to the Z-pole and NuTeV observables with ε and the oblique correction parameters S and T . Compared to a fit with S and T only, inclusion of ε leads to a dramatic improvement in the quality of the fit. The values of S and T preferred by the fit can be obtained within the SM by a simple increase in the Higgs boson mass. However, if the W mass is also included in the fit, a non-zero U parameter becomes necessary which cannot be supplied within the SM. The preferred value of ε suggests that the seesaw mechanism may not be the reason why neutrinos are so light.
In a recent paper, we pointed out that mixing of the light neutrinos with heavy gauge singlet sta... more In a recent paper, we pointed out that mixing of the light neutrinos with heavy gauge singlet states could reconcile the Z-pole data from e+e- colliders and the nu_mu (anti-nu_mu) scattering data from the NuTeV experiment at Fermilab. We further noted that the mixing angle required to fit the data is much larger than what would be expected from the conventional seesaw mechanism. In this paper, we show how such mixings can be arranged by a judicious choice of the neutrino mass texture. We also argue that by invoking the unification of the Dirac mass matrix for the up-type quarks and the neutrinos, the mass of the heavy states can naturally be expected to be in the few TeV range. The model is strongly constrained by the lepton flavor changing process mu -> e gamma which requires lepton universality to be violated in the charged channel.
We analyze the one loop corrections to hadronic Z decays in an R-parity violating extension to th... more We analyze the one loop corrections to hadronic Z decays in an R-parity violating extension to the Minimal Supersymmetric Standard Model (MSSM). Performing a global fit to all the hadronic observables at the Z-peak, we obtain stringent constraints on the R-violating coupling constants λ ′ and λ ′′ . The presence of these couplings worsens the agreement with the data relative to the Standard Model. The strongest constraints come from the b asymmetry parameters A b and A FB (b). From a classical statistical analysis we find that the couplings λ ′ i31 , λ ′ i32 , and λ ′′ 321 are ruled out at the 1σ level, and that λ ′ i33 and λ ′′ 33i are ruled out at the 2σ level. We also obtain Bayesian confidence limits for the R-violating couplings.
We review the current status of precision electroweak measurements and the constraints they impos... more We review the current status of precision electroweak measurements and the constraints they impose on new physics. We perform a model independent analysis using the STU-formalism of Ref. 1, and then discuss how the Z-pole data from LEP and SLD can be used to constrain models that are not covered within that framework.
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Papers by Will Loinaz