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Thomas G. Rizzo

Publications and source records attributed to Thomas G. Rizzo.

At least 127 records · Page 7Linked to original sources
arXiv2001

Cartography with Accelerators: Locating Fermions in Extra Dimensions at Future Lepton Colliders

In the model of Arkani-Hamed and Schmaltz the various chiral fermions of the Standard Model(SM) are localized at different points on a thick wall which forms an extra dimension. Such a scenario provides a way of understanding the absence of proton decay and the fermion mass hierarchy in models with extra dimensions. In this paper we explore the capability of future lepton colliders to determine the location of these fermions in the extra dimension through precision measurements of conventional scattering processes both below and on top of the lowest lying Kaluza-Klein gauge boson resonance. We show that for some classes of models the locations of these fermions can be very precisely determined while in others only their relative positions can be well measured.

hep-ph↗
arXiv2000

Randall-Sundrum Phenomenology at Linear Colliders

The physics of the Randall-Sundrum model relevant for future linear colliders is briefly summarized. The differences between the case where Standard Model(SM) fields are on the wall and where they are in the bulk are emphasized.

hep-ph↗
arXiv2000

New Physics Beyond the Standard Model at $γγ$ Colliders

The complementarity of $e^+e^-$ and $γγ$ colliders to discover and explore new physics beyond the Standard Model(SM) is discussed. After briefly surveying a number of various new physics scenarios we concentrate in detail on signatures for Large Extra Dimensions via the process $γγ\to WW$.

hep-ph↗
arXiv2000

Z' Bosons and Kaluza-Klein Excitations at Muon Colliders

After an extremely brief overview of the discovery reach for Z' bosons, we will discuss the physics of Kaluza-Klein(KK) excitations of the Standard Model gauge bosons that can be explored by a high energy muon collider in the era after the LHC and TeV Linear Collider. We demonstrate that the muon collider is a necessary ingredient in the unraveling the properties of such KK states and, perhaps, proving their existence.

hep-ph↗
arXiv1999

Kaluza-Klein Physics at Muon Colliders

We discuss the physics of Kaluza-Klein excitations of the Standard Model gauge bosons that can be explored by a high energy muon collider in the era after the LHC and TeV Linear Collider. We demonstrate that the muon collider is a necessary ingredient in the unraveling the properties of such states and, perhaps, proving their existence. The possibility of observing the resonances associated with the excited KK graviton states of the Randall-Sundrum model is also discussed.

hep-ph↗
arXiv1999

Testing the Nature of Kaluza-Klein Excitations at Future Lepton Colliders

With one extra dimension, current high precision electroweak data constrain the masses of the first Kaluza-Klein excitations of the Standard Model gauge fields to lie above $\simeq 4$ TeV. States with masses not much larger than this should be observable at the LHC. However, even for first excitation masses close to this lower bound, the second set of excitations will be too heavy to be produced thus eliminating the possibility of realizing the cleanest signature for KK scenarios. Previous studies of heavy $Z'$ and $W'$ production in this mass range at the LHC have demonstrated that very little information can be obtained about their couplings to the conventional fermions given the limited available statistics and imply that the LHC cannot distinguish an ordinary $Z'$ from the degenerate pair of the first KK excitations of the $γ$ and $Z$. In this paper we discuss the capability of lepton colliders with center of mass energies significantly below the excitation mass to resolve this ambiguity. In addition, we examine how direct measurements obtained on and near the top of the first excitation peak at lepton colliders can confirm these results. For more than one extra dimension we demonstrate that it is likely that the first KK excitation is too massive to be produced at the LHC.

hep-ph↗
arXiv1999

Tests of Low Scale Quantum Gravity in $e^-e^-$ and $γγ$ Collisions

Arkani-Hamed, Dimopoulos and Dvali have recently proposed that gravity may become strong at energies near 1 TeV due to the existence of large extra dimensions thus `removing' the hierarchy problem. In this talk we examine the exchange of towers of Kaluza-Klein gravitons and their influence on Moller scattering as well as the production of pairs of massive gauge bosons in $γγ$ collisions. These tower exchanges lead to a set of new dimension-8 operators that can significant alter the Standard Model expectations for these processes. In the case of $γγ$ collisions, the role of polarization for both the initial state photons and the final state gauge bosons in improving sensitivity to graviton exchange is emphasized.

hep-ph↗
arXiv1999

Polarization Asymmetries in $γe$ Collisions and Triple Gauge Boson Couplings Revisited

The capability of the NLC run in the $γe$ collision mode to probe the CP-conserving $γWW$ and $γZZ$ anomalous couplings through the use of the polarization asymmetry is reviewed. When combined with other measurements, very strong constraints on both varieties of anomalous couplings can be obtained. We show that these bounds are complementary to those that can be extracted from data taken at the LHC.

hep-ph↗
arXiv1999

Distinguishing Indirect Signatures Arising From New Physics at the NLC

Many sources of new physics can lead to shifts in the Standard Model predictions for cross sections and asymmetries at the NLC below their direct production thresholds. In this talk we discuss some of the tools that are useful for distinguishing amongst these new physics scenarios. R-parity violation and extensions of the Standard Model gauge structure are two typical non-minimal realizations of supersymmetry which provide us with an important test case to examine.

hep-ph↗
arXiv1999

Electroweak precision measurements and collider probes of the Standard Model with large extra dimensions

The elementary particles of the Standard Model may live in more than 3+1 dimensions. We study the consequences of large compactified dimensions on scattering and decay observables at high-energy colliders. Our analysis includes global fits to electroweak precision data, indirect tests at high-energy electron-positron colliders (LEP2 and NLC), and direct probes of the Kaluza-Klein resonances at hadron colliders (Tevatron and LHC). The present limits depend sensitively on the Higgs sector, both the mass of the Higgs boson and how many dimensions it feels. If the Higgs boson is trapped on a 3+1 dimensional wall with the fermions, large Higgs masses (up to 500 GeV) and relatively light Kaluza-Klein mass scales (less than 4 TeV) can provide a good fit to precision data. That is, a light Higgs boson is not necessary to fit the electroweak precision data, as it is in the Standard Model. If the Higgs boson propagates in higher dimensions, precision data prefer a light Higgs boson (less than 260 GeV), and a higher compactification scale (greater than 3.8 TeV). Future colliders can probe much larger scales. For example, a 1.5 TeV electron-positron linear collider can indirectly discover Kaluza-Klein excitations up to 31 TeV if 500 fb^-1 integrated luminosity is obtained.

hep-ph↗
arXiv1999

Tests of Low Scale Gravity via Gauge Boson Pair Production in $γγ$ Collisions

Arkani-Hamed, Dimopoulos and Dvali have recently proposed that gravity may become strong at energies near 1 TeV thus removing the hierarchy problem. This scenario can be tested in several ways at present and future colliders. In this paper we examine the exchange of towers of Kaluza-Klein gravitons and their influence on the production of pairs of massive gauge bosons in $γγ$ collisions. These tower exchanges are shown to lead to a new dimension-8 operator that can significant alter the Standard Model expectations for these processes. The role of polarization for both the initial state photons and the final state gauge bosons in improving sensitivity to graviton exchange is emphasized. We find that the discovery reach for graviton tower exchange in the $γγ\to W^+W^-$ channel to be significantly greater than for any other process so far examined.

hep-ph↗
arXiv1999

Using Scalars to Probe Theories of Low Scale Quantum Gravity

Arkani-Hamed, Dimopoulos and Dvali have recently suggested that gravity may become strong at energies near 1 TeV which would remove the hierarchy problem. Such a scenario can be tested at present and future colliders since the exchange of towers of Kaluza-Klein gravitons leads to a set of new dimension-8 operators that can play important phenomenological roles. In this paper we examine how the production of pairs of scalars at $e^+e^-$, $γγ$ and hadron colliders can be used to further probe the effects of graviton tower exchange. In particular we examine the tree-level production of pairs of identical Higgs fields which occurs only at the loop level in both the Standard Model and its extension to the Minimal Supersymmetric Standard Model. Cross sections for such processes are found to be potentially large at the LHC and the next generation of linear colliders. For the $γγ$ case the role of polarization in improving sensitivity to graviton exchange is emphasized.

hep-ph↗
arXiv1999

More and More Indirect Signals for Extra Dimensions at More and and More Colliders

It has been recently suggested by Arkani-Hamed, Dimopoulos and Dvali that gravity may become strong at energies not far above the electroweak scale and thus remove the hierarchy problem. Such a scenario can be tested at both present and future accelerators since towers of Kaluza-Klein gravitons and associated scalar fields now play an important phenomenological role. In this paper we examine several processes for their sensitivity to a low scale for quantum gravity including deep inelastic $ep$ scattering at HERA, high precision low energy $νN$ scattering, Bhabha and Moller scattering at linear colliders and both fermion and gluon pair production at $γγ$ colliders.

hep-ph↗
arXiv1999

Top Quark Production at the Tevatron: Probing Anomalous Chromomagnetic Moments and Theories of Low Scale Gravity

We review the effects of an anomalous chromomagnetic moment on top quark pair production at the Tevatron for Run II. Apart from an overall rescaling by the total cross section these couplings have little influence on top production characteristics. We then examine how the exchange of a Kaluza-Klein tower of gravitons arising from the low scale quantum gravity scenario of Arkani-Hamed, Dimopoulos and Dvali influences top pair cross sections and several associated kinematical distributions. The data that will be available with Run II luminosities is shown to be sensitive to values of the effective Planck scale of order 1 TeV or more.

hep-ph↗
arXiv1999

Distinguishing Indirect Signatures of New Physics at the NLC: Z' Versus R-Parity Violation

R-parity violation and extensions of the Standard Model gauge structure offer two non-minimal realizations of supersymmetry at low energies that can lead to similar new physics signatures at existing and future colliders. We discuss techniques that can be employed at the NLC below direct production threshold to distinguish these two new physics scenarios.

hep-ph↗
arXiv1998

Rare K Decays and New Physics Beyond the Standard Model

Rare decays provide a complementary window to direct collider searches as probes of physics beyond the Standard Model. We present an overview of the New Physics sensitivity provided by existing and future measurements of rare leptonic and semileptonic $K$ decays within the context of several classes of models.

hep-ph↗