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Black Hole Production at the LHC by Standard Model Bulk Fields in the Randall-Sundrum Model.

Description: We consider the production of black holes at the LHC in the Randall-Sundrum (RS) model through the collisions of Standard Model(SM) fields in the bulk. In comparison to the previously studied case where the SM fields are all confined to the TeV brane, we find substantial suppressions to the corresponding collider cross sections for all initial states, i.e., gg, qq and gq, where q represents a light quark or anti-quark which lie close to the Planck brane. For b quarks, which are closer to the TeV brane, this suppression effect is somewhat weaker though b quark contributions to the cross section are already quite small due to their relatively small parton densities. Semi-quantitatively, we find that the overall black hole cross section is reduced by roughly two orders of magnitude in comparison to the traditional TeV brane localized RS model with the exact value being sensitive to the detailed localizations of the light SM fermions in the bulk.
Date: November 27, 2006
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Unique Identification of Lee-Wick Gauge Bosons at Linear Colliders

Description: Grinstein, O'Connell and Wise have recently presented an extension of the Standard Model (SM), based on the ideas of Lee and Wick (LW), which demonstrates an interesting way to remove the quadratically divergent contributions to the Higgs mass induced by radiative corrections. This model predicts the existence of negative-norm copies of the usual SM fields at the TeV scale with ghost-like propagators and negative decay widths, but with otherwise SM-like couplings. In earlier work, it was demonstrated that the LW states in the gauge boson sector of these models, though easy to observe, cannot be uniquely identified as such at the LHC. In this paper, we address the issue of whether or not this problem can be resolved at an e{sup +}e{sup -} collider with a suitable center of mass energy range. We find that measurements of the cross section and the left-right polarization asymmetry associated with Bhabha scattering can lead to a unique identification of the neutral electroweak gauge bosons of the Lee-Wick type.
Date: December 14, 2007
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Unique Signatures of Unparticle Resonances at the LHC

Description: The coupling of unparticles to the Standard Model (SM) Higgs boson leads to a breaking of conformal symmetry which produces an effective mass term in the unparticle propagator. Simultaneously, the unparticle couplings to other SM fields produces an effective unparticle decay width via one-loop self-energy graphs. The resulting unparticle propagator then leads to a rather unique appearance for the shape of unparticle resonances that are not of the usual Breit-Wigner type when they form in high energy collisions. In this paper we explore whether or not such resonances, appearing in the Drell-Yan channel at the LHC, can be differentiated from more conventional Z{prime}-like structures which are representative of the typical Breit-Wigner lineshape. We will demonstrate that even with the high integrated luminosities available at the LHC it may be difficult to differentiate these two types of resonance structures for a substantial range of the unparticle model parameters.
Date: September 30, 2008
Creator: Rizzo, Thomas 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

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 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

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

Z' Physics at the LHC and the LHeC

Description: The methods which can be employed to determine the properties of new neutral resonant states that may be observed in the Drell-Yan channel at the LHC are reviewed. If these states are sufficiently light we discuss how polarized ep scattering at the LHeC can assist in the determination of their couplings to the Standard Model (SM) fermions.
Date: August 18, 2008
Creator: Rizzo, Thomas G
Partner: UNT Libraries Government Documents Department

Z' Phenomenology and the LHC

Description: A brief pedagogical overview of the phenomenology of Z{prime} gauge bosons is ILC in determining Z{prime} properties is also discussed. and explore in detail how the LHC may discover and help elucidate the models, review the current constraints on the possible properties of a Z{prime} nature of these new particles. We provide an overview of the Z{prime} studies presented. Such particles can arise in various electroweak extensions of that have been performed by both ATLAS and CMS. The role of the the Standard Model (SM). We provide a quick survey of a number of Z{prime}.
Date: October 17, 2006
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Searching for Lee-Wick Gauge Bosons at the LHC

Description: In an extension of the Standard Model(SM) based on the ideas of Lee and Wick, Grinstein, O'Connell and Wise have found an interesting way to remove the usual quadratically divergent contributions to the Higgs mass induced by radiative corrections. Phenomenologically, the model predicts the existence of Terascale, negative-norm copies of the usual SM fields with rather unique properties: ghost-like propagators and negative decay widths, but with otherwise SM-like couplings. The model is both unitary and causal on macroscopic scales. In this paper we examine whether or not such states with these unusual properties can be uniquely identified as such at the LHC. We find that in the extended strong and electroweak gauge boson sector of the model, which is the simplest one to analyze, such an identification can be rather difficult. Observation of heavy gluon-like resonances in the dijet channel offers the best hope for this identification.
Date: April 30, 2007
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Transverse Beam Polarizationas an Alternate View into New Physics at CLIC

Description: In e{sup +}e{sup -} collisions, transverse beam polarization can be a useful tool in studying the properties of particles associated with new physics beyond the Standard Model(SM). However, unlike in the case of measurements associated with longitudinal polarization, the formation of azimuthal asymmetries used to probe this physics in the case of transverse polarization requires both e{sup {+-}} beams to be simultaneously polarized. In this paper we discuss the further use of transverse polarization as a probe of new physics models at a high energy, {radical}s = 3 TeV version of CLIC. In particular, we show (i) how measurements of the sign of these asymmetries is sufficient to discriminate the production of spin-0 supersymmetric states from the spin-1/2 Kaluza-Klein excitations of Universal Extra Dimensions. Simultaneously, the contribution to this asymmetry arising from the potentially large SM W{sup +}W{sup -} background can be made negligibly small. We then show (ii) how measurements of such asymmetries and their associated angular distributions on the peak of a new resonant Z{prime}-like state can be used to extract precision information on the Z{prime} couplings to the SM fermions.
Date: August 12, 2011
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

TeV Scale Black Holes in Warped Higher-Curvature Gravity

Description: We examine the properties of TeV-scale extra dimensional black holes (BH) in Randall-Sundrum-like models with Gauss-Bonnet higher-curvature terms present in the action. These theories naturally lead to a mass threshold for BH production in TeV particle collisions which could be observable at LHC/ILC. The lifetimes of such BH are examined and, in particular, we focus on the predicted lifetime differences between the canonical and microcanonical thermodynamical descriptions of BH decaying to Standard Model brane fields and the possibility of long-lived relics. The sensitivity of these results to the particular mix of fermions and bosons present in the Standard Model spectrum is also briefly examined.
Date: November 9, 2005
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Introduction to Extra Dimensions

Description: Extra dimensions provide a very useful tool in addressing a number of the fundamental problems faced by the Standard Model. The following provides a very basic introduction to this very broad subject area as given at the VIII School of the Gravitational and Mathematical Physics Division of the Mexican Physical Society in December 2009. Some prospects for extra dimensional searches at the 7 TeV LHC with {approx}1 fb{sup -1} of integrated luminosity are provided.
Date: April 29, 2010
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Light Squarks and Gluinos at TeV-scale $e^+e^-$ Colliders

Description: In the general MSSM, first and second generation squarks and gluinos may be sufficiently light to be produced and studied at e{sup +}e{sup -} colliders operating in the 0.5-1 TeV energy range. After a reminder that the MSSM is not the same as mSUGRA, we provide a brief overview of these possibilities within this more general framework. Squarks and gluinos may be light enough to be produced at an e{sup +}e{sup -} collider operating in the 0.5-1 TeV energy range in non-mSUGRA SUSY breaking scenarios. The decays of such particles, though always leading to jets, may or may not produce ME depending on the nature of the SUSY spectrum. The electroweak properties of the squarks can be determined using polarized beams and production cross section measurements. The simultaneous production of essentially degenerate 1st and 2nd generation squarks can be problematic although efficient charm tagging would be helpful. If (some) squarks are heavier than gluinos then gluinos may be best studied as squark decay products. If gluinos are heavier than squarks, associated production can lead to an unambiguous, although small, production cross section somewhat below {approx} 1 fb. Gluino pair production is perhaps more interesting as the cross section for this process involves the entire strongly interacting sector of the MSSM. The rate is expected to be rather small for this process in the case of mSUGRA but has not been well-studied in the more general MSSM.
Date: August 19, 2011
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Lorentz Violation in Warped Extra Dimensions

Description: Higher dimensional theories which address some of the problematic issues of the Standard Model(SM) naturally involve some form of D = 4 + n-dimensional Lorentz invariance violation (LIV). In such models the fundamental physics which leads to, e.g., field localization, orbifolding, the existence of brane terms and the compactification process all can introduce LIV in the higher dimensional theory while still preserving 4-d Lorentz invariance. In this paper, attempting to capture some of this physics, we extend our previous analysis of LIV in 5-d UED-type models to those with 5- d warped extra dimensions. To be specific, we employ the 5-d analog of the SM Extension of Kostelecky et al. which incorporates a complete set of operators arising from spontaneous LIV. We show that while the response of the bulk scalar, fermion and gauge fields to the addition of LIV operators in warped models is qualitatively similar to what happens in the flat 5-d UED case, the gravity sector of these models reacts very differently than in flat space. Specifically, we show that LIV in this warped case leads to a non-zero bulk mass for the 5-d graviton and so the would-be zero mode, which we identify as the usual 4-d graviton, must necessarily become massive. The origin of this mass term is the simultaneous existence of the constant non-zero AdS{sub 5} curvature and the loss of general co-ordinate invariance via LIV in the 5-d theory. Thus warped 5-d models with LIV in the gravity sector are not phenomenologically viable.
Date: August 11, 2011
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Indirect Searches for Z'-like Resonances at the LHC

Description: We explore the possibility of indirectly observing the effects of Z{prime}-like particles with electroweak strength couplings in the Drell-Yan channel at the LHC with masses above the resonance direct search reach. We find that, mostly due to statistical limitations, this is very unlikely in almost all classes of models independently of the spin of the resonance. Not unexpectedly, the one exception to this general result is the case of degenerate Kaluza-Klein (KK) excitations of the photon and Z that occur in some extra-dimensional models. In this special case, the strong destructive interference with the Standard Model (SM) exchanges below the resonance mass leads to a well-known significant suppression of the cross section and thus increased sensitivity to this particular new physics scenario.
Date: June 19, 2009
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Identification of the Origin of Monojet Signatures at the LHC

Description: Several new physics scenarios can lead to monojet signatures at the LHC. If such events are observed above the Standard Model background it will be important to identify their origin. In this paper we compare and contrast these signatures as produced in two very different pictures: vector or scalar unparticle production in the scale-invariant/conformal regime and graviton emission in the Arkani-Hamed, Dimopoulos and Dvali extra-dimensional model. We demonstrate that these two scenarios can be distinguished at the LHC for a reasonable range of model parameters through the shape of their respective monojet and/or missing E{sub T} distributions.
Date: May 13, 2008
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Tev-Scale Black Hole Lifetimes in Extra-Dimensional Lovelock Gravity

Description: We examine the mass loss rates and lifetimes of TeV-scale extra dimensional black holes (BH) in ADD-like models with Lovelock higher-curvature terms present in the action. In particular we focus on the predicted differences between the canonical and microcanonical ensemble statistical mechanics descriptions of the Hawking radiation that results in the decay of these BH. In even numbers of extra dimensions the employment of the microcanonical approach is shown to generally lead to a significant increase in the BH lifetime as in case of the Einstein-Hilbert action. For odd numbers of extra dimensions, stable BH remnants occur when employing either description provided the highest order allowed Lovelock invariant is present. However, in this case, the time dependence of the mass loss rates obtained employing the two approaches will be different. These effects are in principle measurable at future colliders.
Date: January 5, 2006
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Higher Curvature Effects in the ADD and RS Models

Description: Over the last few years several extra-dimensional models have been introduced in attempt to deal with the hierarchy problem. These models can lead to rather unique and spectacular signatures at Terascale colliders such as the LHC and ILC. The ADD and RS models, though quite distinct, have many common feature including a constant curvature bulk, localized Standard Model(SM) fields and the assumption of the validity of the EH action as a description of gravitational interactions.
Date: July 5, 2006
Creator: Rizzo, Thomas G.
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

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

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