arXiv subjects

Thomas G. Rizzo

Publications and source records attributed to Thomas G. Rizzo.

At least 109 records · Page 6Linked to original sources

arXiv2003

More Transverse Polarization Signatures of Extra Dimensions at Linear Colliders

Polarization of both electron and positron beams at a future linear collider (LC) allows for the measurement of transverse polarization asymmetries. These asymmetries have been shown to be particularly sensitive to graviton or other spin-2, $s-$channel exchanges in the process $e^+e^- \to f\bar f (f\neq e)$ which allows for a doubling of the usual search reach. A question then arises as to whether other $e^+e^-$ processes also show comparable sensitivity. Here we extend our previous analysis to the set of final states $e^+e^-, W^+W^-,~2γ$ and $~2Z$ as well as to the Møller scattering process $e^-e^-\to e^-e^-$. We demonstrate that these reactions yield transverse polarization asymmetries which are somewhat less sensitive to graviton exchange than are those obtained in our earlier analysis for $e^+e^-\to f\bar f$.

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arXiv2003

Contact Interaction Searches at the Linear Collider: Energy, Luminosity and Positron Polarization Dependencies

Many types of new physics can lead to contact interaction-like modifications in $e^+e^-$ processes below direct production threshold. This report summarizes a survey of contact interaction search reaches at the Linear Collider as functions of energy, luminosity and positron polarization. The various tradeoffs between these quantities in such searches are examined in detail.

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arXiv2002

Transverse Polarization Signatures of Extra Dimensions at Linear Colliders

If significant longitudinal polarization of both the electrons and positrons becomes feasible at a future linear collider(LC), it may be possible to use spin rotators to produce transversely polarized beams. Using the transverse polarization of both beams, new azimuthal spin asymmetries can be formed which will be sensitive probes for new physics beyond the Standard Model. Here we demonstrate that these asymmetries are particularly sensitive to the exchange of Kaluza-Klein towers of gravitons, or other spin-2 fields, that are predicted to exist in higher dimensional theories which address the hierarchy problem. These new asymmetries are shown to be able to extend the search reach for such new physics by more than a factor of two, provide an additional tool for isolating the signatures for spin-2 exchange up to mass scales in excess of $10\sqrt s$, and can be used to help differentiate among the proposed solutions to the hierarchy problem below the production threshold for new particles.

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arXiv2002

Effects of Radion Mixing on the Standard Model Higgs Boson

We discuss how mixing between the Standard Model Higgs boson and the radion of the Randall-Sundrum model can lead to significant shifts in the expected properties of the Higgs boson. In particular we show that the total and partial decay widths of the Higgs, as well as the $h\to gg$ branching fraction, can be substantially altered from their SM expectations, while the remaining branching fractions are modified less than about 5% for most of the parameter space volume. Precision measurements of Higgs boson properties at at a Linear Collider are shown to probe a large region of the Randall-Sundrum model parameter space.

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arXiv2002

Unique Graviton Exchange Signatures at Linear Colliders

Many types of new physics can lead to contact interaction-like modifications in $e^+e^-$ processes below direct production threshold. We examine the possibility of uniquely identifying the effects of graviton exchange from amongst this large set of models by using the moments of the angular distribution of the final state particles. In the case of $e^+e^-\to f\bar f(W^+W^-)$ we demonstrate that this technique allows for the unique identification of the graviton exchange signature at the $5σ$ level for mass scales as high as $6(2.5)\sqrt s$.

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arXiv2002

Unique Identification of Graviton Exchange Effects in e^+ e^- Collisions

Many types of new physics can lead to contact interaction-like modifications in e^+ e^- processes below direct production threshold. We examine the possibility of uniquely identifying the effects of graviton exchange, which are anticipated in many extra dimensional theories, from amongst this large set of models by using the moments of the angular distribution of the final state particles. In the case of the e^+ e^- --> f bar{f} process we demonstrate that this technique allows for the unique identification of the graviton exchange signature at the 5 sigma level for mass scales as high as 6 sqrt(s). The extension of this method to the e^+ e^- --> W^+ W^- process is also discussed.

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arXiv2002

Effects on Higgs Boson Properties From Radion Mixing

We discuss how mixing between the Standard Model Higgs boson, $h$, and the radion of the Randall-Sundrum model can lead to significant shifts in the expected properties of the Higgs boson. In particular we show that the total and partial decay widths of the Higgs, as well as the $h\to gg$ branching fraction, can be substantially altered from their SM expectations, while the remaining branching fractions are modified less than $\lsim 5%$ for most of the parameter space volume. Precision measurements of Higgs boson properties at at a Linear Collider are shown to probe a large region of the Randall-Sundrum model parameter space.

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arXiv2002

Radion Couplings to Bulk Fields in the Randall-Sundrum Model

The radion may be the lightest new state present in the Randall-Sundrum(RS) model. We examine the couplings of the radion to the Standard Model(SM) fields in the scenario where they propagate in the bulk and expand into Kaluza-Klein towers. These couplings are then contrasted with those of the more familiar case where the SM fields are confined to the TeV brane. We find that the couplings of the radion to both $gg$ and $γγ$ can be significantly different in these two cases. Implications for radion collider phenomenology are discussed.

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arXiv2002

Signals for Noncommutative QED at Future $e^+e^-$ Colliders

The signatures for noncommutative QED at $e^+e^-$ colliders with center of mass energies in the range of 0.5-5 TeV are examined. For integrated luminosities of 0.5-1 ab$^{-1}$ or more, sensitivities to the associated mass scales greater than $\sqrt s$ are possible.

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arXiv2002

Black Hole Production at the LHC: Effects of Voloshin Suppression

We examine the rates for the production of black holes(BH) at the LHC in light of the exponential suppression of the geometric cross section estimate recently proposed by Voloshin. We show that the resulting production rates will still be quite large over a reasonably wide range of model parameters. While BH production may no longer be the dominant collider process, its unique signature will ensure observability over more conventional backgrounds.

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arXiv2001

Black Hole Production Rates at the LHC: Still Large

We examine the rates for the production of black holes(BH) at the LHC in light of the exponential suppression of the geometric cross section estimate proposed by Voloshin. We show that these rates will still be quite large over a reasonable range of model parameters. While BH production may not be the dominant process, its unique signature will ensure observability over conventional backgrounds.

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arXiv2001

Report of the Snowmass Subgroup on Extra Dimensions

In this report we summarize the work performed at Snowmass 2001 on the physics of extra dimensions. We divide these analyses into the following classes: searches for extra dimensional phenomena, identification of specific new physics scenarios, studies of black hole production and non-commutative QED.

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arXiv2001

Identification of Randall-Sundrum Graviton Resonances at Linear Colliders

We discuss several methods which can be used to distinguish the graviton resonances of the Randall-Sundrum model from the graviton-like resonances which may occur in other theories. The Breit-Wigner line shape of the RS graviton is found to be particularly useful. In particular we show that the "effective" graviton resonance present in the model of Dvali et al ~can be distinguished from those of the Randall-Sundrum scenario for a reasonably wide range of model parameters.

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arXiv2001

Distinguishing Kaluza-Klein Resonances From a $Z'$ in Drell-Yan Processes at the LHC

We explore the capability of the LHC to distinguish the production of Kaluza-Klein(KK) excitations in Drell-Yan collisions from an ordinary $Z'$ at the LHC in the case of one extra dimension with the fermions localized at the orbifold fixed points. In particular, we demonstrate that this capability is dependent on both the mass of the KK state as well as whether or not the quarks and leptons lie at the same fixed points.

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arXiv2001

Signals For Extra Dimensions at the VLHC

A brief overview of the signatures for several different models with extra dimensions at the stage II, $\sqrt s=175-200$ TeV VLHC is presented. In all cases the search reaches for these models in the Drell-Yan channel are found to be in the range of 15-80 TeV.

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arXiv2001

Extra Dimensional Signatures for CLIC

A brief overview is presented of the signatures for several different models with extra dimensions at CLIC, an $e^+e^-$ linear collider with a center of mass energy of 3-5 TeV and an integrated luminosity of order 1 $ab^{-1}$. In all cases the search reach for the resulting new physics signatures is found to be in the range of $\simeq$15-80 TeV.

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arXiv2001

Probes Of Universal Extra Dimensions at Colliders

In the Universal Extra Dimensions model of Appelquist, Cheng and Dobrescu, all of the Standard Model fields are placed in the bulk and thus have Kaluza-Klein(KK) excitations. These KK states can only be pair produced at colliders due to the tree-level conservation of KK number, with the lightest of them being stable and possibly having a mass as low as $\simeq 350-400$ GeV. After calculating the contribution to $g-2$ in this model we investigate the production cross sections and signatures for these particles at both hadron and lepton colliders. We demonstrate that these signatures critically depend upon whether the lightest KK states remain stable or are allowed to decay by any of a number of new physics mechanisms. These mechanisms which induce KK decays are studied in detail.

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arXiv2001

Bulk Physics at a Graviton Factory

A general prediction of the 5-d Randall-Sundrum (RS) hierarchy model is the emergence of spin-2 Kaluza Klein (KK) gravitons with weak scale masses and couplings. The lowest order effective theory of the RS model is given by 5-d Einstein gravity which uniquely fixes the self-interactions of gravitons. We demonstrate that large numbers of light KK resonances could be produced at a future lepton-collider-based ``Graviton Factory''. Measuring the self-interactions of these KK gravitons will probe the accuracy of the 5-d Einstein gravity picture and, in addition, yield indirect information on the as yet untested self-coupling of the 4-d graviton. The self-interactions of the gravitons can be studied by measuring the decays of the heavier states to the lighter ones. Using the AdS/CFT picture, these can be interpretted as the decays of heavier resonances to lighter ones, in a strongly coupled 4-d CFT. We show that these decays have sufficient rates to be studied at future colliders and that they are also, in principle, sensitive to higher derivative operators, such as the Gauss-Bonnet term. In a generalized RS model, with non-universal 5-d fermion masses, FCNC's will be induced. We show that precise measurements of the rare decays of KK graviton/gauge states into flavor non-diagonal final states at a Graviton Factory can be used to map the 5-d fermion mass matrix.

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