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SUSY Without Prejudice

Description: We begin an exploration of the physics associated with the general CP-conserving MSSM with Minimal Flavor Violation, the pMSSM. The 19 soft SUSY breaking parameters in this scenario are chosen so as to satisfy all existing experimental and theoretical constraints assuming that the WIMP is a thermal relic, i.e., the lightest neutralino. We scan this parameter space twice using both flat and log priors for the soft SUSY breaking mass parameters and compare the results which yield similar conclusions. Detailed constraints from both LEP and the Tevatron searches play a particularly important role in obtaining our final model samples. We find that the pMSSM leads to a much broader set of predictions for the properties of the SUSY partners as well as for a number of experimental observables than those found in any of the conventional SUSY breaking scenarios such as mSUGRA. This set of models can easily lead to atypical expectations for SUSY signals at the LHC.
Date: December 11, 2008
Creator: Berger, C.F.; Gainer, J.S.; Hewett, J.L. & Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

SUSY Without Prejudice at Linear Colliders

Description: We explore the physics of the general CP-conserving MSSM with Minimal Flavor Violation, the pMSSM. The 19 soft SUSY breaking parameters are chosen so to satisfy all existing experimental and theoretical constraints assuming that the WIMP is the lightest neutralino. We scan this parameter space twice using both flat and log priors and compare the results which yield similar conclusions. Constraints from both LEP and the Tevatron play an important role in obtaining our final model samples. Implications for future TeV-scale e{sup +}e{sup -} linear colliders (LC) are discussed.
Date: December 11, 2008
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

On Direct Verification of Warped Hierarchy-and-FlavorModels

Description: We consider direct experimental verification of warped models, based on the Randall-Sundrum (RS) scenario, that explain gauge and flavor hierarchies, assuming that the gauge fields and fermions of the Standard Model (SM) propagate in the 5D bulk. Most studies have focused on the bosonic Kaluza Klein (KK) signatures and indicate that discovering gauge KK modes is likely possible, yet challenging, while graviton KK modes are unlikely to be accessible at the LHC, even with a luminosity upgrade. We show that direct evidence for bulk SM fermions, i.e. their KK modes, is likely also beyond the reach of a luminosity-upgraded LHC. Thus, neither the spin-2 KK graviton, the most distinct RS signal, nor the KK SM fermions, direct evidence for bulk flavor, seem to be within the reach of the LHC. We then consider hadron colliders with vs. = 21, 28, and 60 TeV. We find that discovering the first KK modes of SM fermions and the graviton typically requires the Next Hadron Collider (NHC) with {radical}s {approx} 60 TeV and O(1) ab-1 of integrated luminosity. If the LHC yields hints of these warped models, establishing that Nature is described by them, or their 4D CFT duals, requires an NHC-class machine in the post-LHC experimental program.
Date: October 15, 2007
Creator: Davoudiasl, Hooman; /Brookhaven; Rizzo, Thomas G.; /SLAC; Soni, Amarjit & /Brookhaven
Partner: UNT Libraries Government Documents Department

Minimal Direct Gauge Mediation

Description: We propose a simple model of gauge mediation with a small gravitino mass, m{sub 3/2} < O(10) eV, where supersymmetry is broken by a strong dynamics at O(10) TeV.
Date: November 7, 2007
Creator: Ibe, Masahiro & Kitano, Ryuichiro
Partner: UNT Libraries Government Documents Department

Signatures of Spherical Compactifications at the LHC

Description: TeV-scale extra dimensions may play an important role in electroweak or supersymmetry breaking. We examine the phenomenology of such dimensions, compactified on a sphere S{sup n}, n {ge} 2, and show that they possess distinct features and signatures. For example, unlike flat toroidal manifolds, spheres do not trivially allow fermion massless modes. Acceptable phenomenology then generically leads to ''non-universal'' extra dimensions with ''pole-localized'' 4-d fermions; the bosonic fields can be in the bulk. Due to spherical symmetry, some Kaluza-Klein (KK) modes of bulk gauge fields are either stable or extremely long-lived, depending on the graviton KK spectrum. Using precision electroweak data, we constrain the lightest gauge field KK modes to lie above {approx_equal} 4 TeV. We show that some of these KK resonances are within the reach of the LHC in several different production channels. The models we study can be uniquely identified by their collider signatures.
Date: February 12, 2007
Creator: Davoudiasl, Hooman & Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Higher Curvature Gravity in TeV-Scale Extra Dimensions

Description: We begin a general exploration of the phenomenology of TeV-scale extra-dimensional models with gravitational actions that contain higher curvature terms. In particular, we examine how the classic collider signatures of the models of Arkani-Hamed, Dimopoulos and Dvali (missing energy and new dimension-8 contact interactions) and of Randall and Sundrum (TeV-scale graviton Kaluza-Klein resonances) are altered by these modifications to the usual Einstein-Hilbert action. We find that not only are the detailed signatures for these gravitationally induced processes altered but new contributions are found to arise due to the existence of additional scalar Kaluza-Klein states in the spectrum.
Date: March 31, 2006
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

The LHC Inverse Problem, Supersymmetry and the ILC

Description: We address the question whether the ILC can resolve the LHC Inverse Problem within the framework of the MSSM. We examine 242 points in the MSSM parameter space which were generated at random and were found to give indistinguishable signatures at the LHC. After a realistic simulation including full Standard Model backgrounds and a fast detector simulation, we find that roughly only one third of these scenarios lead to visible signatures of some kind with a significance {ge} 5 at the ILC with {radical}s = 500 GeV. Furthermore, we examine these points in parameter space pairwise and find that only one third of the pairs are distinguishable at the ILC at 5{sigma}.
Date: November 12, 2007
Creator: Berger, C.F.; Gainer, J.S.; Hewett, J.L.; Lillie, B. & Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Probing the Universal Randall-Sundrum Model at the ILC

Description: The Randall-Sundrum model with all Standard Model (SM) fields in the bulk, including the Higgs, can be probed by precision measurements at the ILC. In particular, the couplings of the Higgs to the gauge bosons of the SM can be determined with high accuracy at the ILC. Here we examine the deviations in these couplings from their SM values within the framework of the Universal Randall-Sundrum Model (URSM) as well as the corresponding couplings of the first Higgs Kaluza-Klein excitation.
Date: December 14, 2005
Creator: Davoudiasl, H.; /Wisconsin U., Madison; Lillie, B.; Rizzo, T.G. & /SLAC
Partner: UNT Libraries Government Documents Department

The Determination of the Helicity of W' Boson Coupling at the LHC

Description: Apart from its mass and width, the most important property of a new charged gauge boson, W{prime}, is the helicity of its couplings to the SM fermions. Such particles are expected to exist in many extensions of the Standard Model. In this paper we explore the capability of the LHC to determine the W{prime} coupling helicity at low integrated luminosities in the {ell} + E{sub T}{sup miss} discovery channel. We find that measurements of the transverse mass distribution, reconstructed from this final state in the W-W{prime} interference region, provides the best determination of this quantity. To make such measurements requires integrated luminosities of {approx} 10(60) fb{sup -1} assuming M{sub W{prime}} = 1.5(2.5) TeV and provided that the W{prime} couplings have Standard Model magnitude. This helicity determination can be further strengthened by the use of various discovery channel leptonic asymmetries, also measured in the same interference regime, but with higher integrated luminosities.
Date: April 6, 2007
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Master Integrals for Fermionic Contributions to Massless Three-Loop Form Factors

Description: In this letter we continue the calculation of master integrals for massless three-loop form factors by giving analytical results for those diagrams which are relevant for the fermionic contributions proportional to N{sub F}{sup 2}, N{sub F} {center_dot} N, and N{sub F}/N. Working in dimensional regularization, we express one of the diagrams in a closed form which is exact to all orders in {epsilon}, containing {Lambda}-functions and hypergeometric functions of unit argument. In all other cases we derive multiple Mellin-Barnes representations from which the coefficients of the Laurent expansion in {epsilon} are extracted in an analytical form. To obtain the finite part of the three-loop quark and gluon form factors, all coefficients through transcendentality six in the Riemann {zeta}-function have to be included.
Date: November 28, 2007
Creator: Heinrich, G.; Huber, T. & Maitre, D.
Partner: UNT Libraries Government Documents Department

Noncommutative Inspired Black Holes in Extra Dimensions

Description: In a recent string theory motivated paper, Nicolini, Smailagic and Spallucci (NSS) presented an interesting model for a noncommutative inspired, Schwarzschild-like black hole solution in 4-dimensions. The essential effect of having noncommutative co-ordinates in this approach is to smear out matter distributions on a scale associated with the turn-on of noncommutativity which was taken to be near the 4-d Planck mass. In particular, NSS assumed that this smearing was essentially Gaussian. This energy scale is sufficiently large that in 4-d such effects may remain invisible indefinitely. Extra dimensional models which attempt to address the gauge hierarchy problem, however, allow for the possibility that the effective fundamental scale may not be far from {approx} 1 TeV, an energy regime that will soon be probed by experiments at both the LHC and ILC. In this paper we generalize the NSS model to the case where flat, toroidally compactified extra dimensions are accessible at the TeV-scale and examine the resulting modifications in black hole properties due to the existence of noncommutativity. We show that while many of the noncommutativity-induced black hole features found in 4-d by NSS persist, in some cases there can be significant modifications due the presence of extra dimensions. We also demonstrate that the essential features of this approach are not particularly sensitive to the Gaussian nature of the smearing assumed by NSS.
Date: June 7, 2006
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

New Dimensions for Randall-Sundrum Phenomenology

Description: We consider a 6D extension of the Randall-Sundrum (RS) model, RS6, where the Standard Model (SM) gauge fields are allowed to propagate in an additional dimension, compactified on S{sup 1} or S{sup 1}/Z{sub 2}. In a minimal scenario, fermions propagate in the 5D RS subspace and their localization provides a model of flavor. New Kaluza-Klein (KK) states, corresponding to excitations of the gauge fields along the 6th dimension, appear near the TeV scale. The new gauge KK modes behave differently from those in the 5D warped models. These RS6 states have couplings with strong dependence on 5D field localization and, within the SM, only interact with heavy fermions and the Higgs sector, to a very good approximation. Thus, the collider phenomenology of the new gauge KK states sensitively depends on the 5D fermion geography. We briefly discuss inclusion of SM fermions in all 6 dimensions, as well as the possibility of going beyond 6D.
Date: September 30, 2008
Creator: Davoudiasl, Hooman & Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Reggeon Non_Factorizability and Fixed Pole in DVCS

Description: We argue that deeply virtual Compton scattering will display Regge behavior {nu}{sub R}{sup {alpha}}(t) at high energy at fixed-t, even at high photon virtuality, not necessarily conventional scaling. A way to see this is to track the Reggeon contributions to quark-nucleon scattering and notice that the resulting Generalized Parton Distributions would have divergent behavior at the break-points. In addition, we show that the direct two-photon to quark coupling will be accessible at large t where it dominates the DVCS amplitude for large energies. This contribution, the J = 0 fixed-pole, should be part of the future DVCS experimental programs at Jlab or LHeC.
Date: August 3, 2009
Creator: Brodsky, Stanley J.; Llanes-Estrada, Felipe J.; Londergan, J.Timothy & Szczepaniak, Adam P.
Partner: UNT Libraries Government Documents Department

Supersymmetric Model Builing (and Sweet Spot Supersymmetry)

Description: It has been more than twenty years since theorists started discussing supersymmetric model building/phenomenology. We review mechanisms of supersymmetry breaking/mediation and problems in each scenario. We propose a simple model to address those problems and discuss its phenomenology.
Date: January 8, 2008
Creator: Ibe, Masahiro; /SLAC /Stanford U., Phys. Dept.; Kitano, Ryuichiro & Alamos, /Los
Partner: UNT Libraries Government Documents Department

Sequestering the Gravitino: Neutralino Dark Matter in Gauge Mediation

Description: In conventional models of gauge-mediated supersymmetry breaking, the lightest supersymmetric particle (LSP) is invariably the gravitino. However, if the supersymmetry breaking sector is strongly coupled, conformal sequestering may raise the mass of the gravitino relative to the remaining soft supersymmetry-breaking masses. In this letter, we demonstrate that such conformal dynamics in gauge-mediated theories may give rise to satisfactory neutralino dark matter while simultaneously solving the flavor and {mu}/B{mu} problems.
Date: August 15, 2008
Creator: Craig, Nathaniel J.; /Stanford U., Dept. Phys.; Green, Daniel & /SLAC /Stanford U., Dept. Phys.
Partner: UNT Libraries Government Documents Department

The First Estimate of BR(\bar B to X_s\gamma) at O(\alpha_s^2)

Description: Combining our results for various {Omicron}({alpha}{sub s}{sup 2}) corrections to the weak radiative B-meson decay, we are able to present the first estimate of the branching ratio at the next-to-next-to-leading order in QCD. We find {Beta}({bar B} {yields} X{sub s}{gamma}) = (3.15 {+-} 0.23) x 10{sup -4} for E{sub {gamma}} > 1.6 GeV in the {bar B}-meson rest frame. The four types of uncertainties: non-perturbative (5%), parametric (3%), higher-order (3%) and m{sub c}-interpolation ambiguity (3%) have been added in quadrature to obtain the total error.
Date: October 24, 2006
Creator: Misiak, M.; Asatrian, H. M.; Bieri, K.; Czakon, M.; Czarnecki, A.; Ewerth, T. et al.
Partner: UNT Libraries Government Documents Department

Direct Probes of Linearly Polarized Gluons inside Unpolarized Hadrons

Description: We show that the unmeasured distribution of linearly polarized gluons inside unpolarized hadrons can be directly probed in jet or heavy quark pair production both in electron-hadron and hadron-hadron collisions. We present expressions for the simplest cos 2{phi} asymmetries and estimate their maximal value in the particular case of electron-hadron collisions. Measurements of the linearly polarized gluon distribution in the proton should be feasible in future EIC or LHeC experiments.
Date: February 7, 2011
Creator: Boer, Daniel; Brodsky, Stanley J.; Mulders, Piet J. & Pisano, Cristian
Partner: UNT Libraries Government Documents Department

Contact Interaction and Resonant-Like Physics at Present and Future Colliders from Unparticles

Description: High scale conformal physics can lead to unusual unparticle stuff at our low energies. In this paper we discuss how the exchange of unparticles between Standard Model fields can lead to new contact interaction physics as well as a pseudoresonance-like structure, an unresonance, that might be observable at the Tevatron or LHC in the Drell-Yan channel. The specific signatures of this scenario are quite unique and can be used to easily identify this new physics given sufficient integrated luminosity.
Date: June 27, 2007
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Application of the Principle of Maximum Conformality to the Top-Quark Forward-Backward Asymmetry at the Tevatron

Description: The renormalization scale uncertainty can be eliminated by the Principle of Maximum Conformality (PMC) in a systematic scheme-independent way. Applying the PMC for the t{bar t}-pair hadroproduction at the NNLO level, we have found that the total cross-sections {sigma}{sub t{bar t}} at both the Tevatron and LHC remain almost unchanged when taking very disparate initial scales {mu}{sub R}{sup init} equal to m{sub t}, 10 m{sub t}, 20 m{sub t} and {radical}s, which is consistent with renormalization group invariance. As an important new application, we apply PMC scale-setting to study the top-quark forward-backward asymmetry. We observe that the more convergent perturbative series after PMC scale-setting leads to a more accurate top-quark forward-backward asymmetry. The resulting PMC prediction on the asymmetry is also free from the initial renormalization scale-dependence. Because the NLO PMC scale has a dip behavior for the (q{bar q})-channel at small subprocess collision energies, the importance of this channel to the asymmetry is increased. We observe that the asymmetries A{sub FB}{sup t{bar t}} and A{sub FB}{sup p{bar p}} at the Tevatron will be increased by 42% in comparison to the previous estimates obtained by using conventional scale-setting; i.e. we obtain A{sub FB}{sup t{bar t}PMC} {approx_equal} 12.5% and A{sub FB}{sup p{bar p},PMC} {approx_equal} 8.28%. Moreover, we obtain A{sub FB}{sup t{bar t}PMC} (M{sub t{bar t}} > 450 GeV) {approx_equal} 35.0%. These predictions have a 1{sigma}-deviation from the present CDF and D0 measurements; the large discrepancies of the top-quark forward-backward asymmetry between the Standard Model estimate and the CDF and D0 data are thus greatly reduced.
Date: May 14, 2012
Creator: Brodsky, Stanley J.; /SLAC; Wu, Xing-Gang & U., /SLAC /Chongqing
Partner: UNT Libraries Government Documents Department

Application of the Principle of Maximum Conformality to Top-Pair Production

Description: A major contribution to the uncertainty of finite-order perturbative QCD predictions is the perceived ambiguity in setting the renormalization scale {mu}{sub r}. For example, by using the conventional way of setting {mu}{sub r} {element_of} [m{sub t}/2, 2m{sub t}], one obtains the total t{bar t} production cross-section {sigma}{sub t{bar t}} with the uncertainty {Delta}{sigma}{sub t{bar t}}/{sigma}{sub t{bar t}} {approx} (+3%/-4%) at the Tevatron and LHC even for the present NNLO level. The Principle of Maximum Conformality (PMC) eliminates the renormalization scale ambiguity in precision tests of Abelian QED and non-Abelian QCD theories. By using the PMC, all nonconformal {l_brace}{beta}{sub i}{r_brace}-terms in the perturbative expansion series are summed into the running coupling constant, and the resulting scale-fixed predictions are independent of the renormalization scheme. The correct scale-displacement between the arguments of different renormalization schemes is automatically set, and the number of active flavors n{sub f} in the {l_brace}{beta}{sub i}{r_brace}-function is correctly determined. The PMC is consistent with the renormalization group property that a physical result is independent of the renormalization scheme and the choice of the initial renormalization scale {mu}{sub r}{sup init}. The PMC scale {mu}{sub r}{sup PMC} is unambiguous at finite order. Any residual dependence on {mu}{sub r}{sup init} for a finite-order calculation will be highly suppressed since the unknown higher-order {l_brace}{beta}{sub i}{r_brace}-terms will be absorbed into the PMC scales higher-order perturbative terms. We find that such renormalization group invariance can be satisfied to high accuracy for {sigma}{sub t{bar t}} at the NNLO level. In this paper we apply PMC scale-setting to predict the t{bar t} cross-section {sigma}{sub t{bar t}} at the Tevatron and LHC colliders. It is found that {sigma}{sub t{bar t}} remains almost unchanged by varying {mu}{sub r}{sup init} within the region of [m{sub t}/4, 4m{sub t}]. The convergence of the expansion series is greatly improved. For the (q{bar ...
Date: May 13, 2013
Creator: Brodsky, Stanley J.; /SLAC; Wu, Xing-Gang & U., /SLAC /Chongqing
Partner: UNT Libraries Government Documents Department