Main linac lattice design and optimization for E_(cm)=1 TeV CLIC

The Compact Linear Collider(CLIC) is a future e+e- linear collider. The CLIC study concentrated on a design of center-of-mass energy of 3 TeV and demonstrated the feasibility of the technology. However, the physics also demands lower energy collision. To satisfy this, CLIC can be built in stages. The actual stages will depend on LHC results. Some specific scenarios of staged constructions have been shown in CLIC Concept Design Report(CDR). In this paper, we concentrate on the main linac lattice design for Ecm=1 TeV CLIC aiming to upgrade from Ecm=500 GeV CLIC and then to Ecm=3 TeV one. This main linac accelerates the electron or positron beam from9 GeV to 500 GeV. A primary lattice design based on the 3 TeV CLIC main linac design and its optimization based on the beam dynamics study will be presented. As we use the same design principles as 3TeV CLIC main linac, this optimization is basically identical to the 3 TeV one. All the simulations results are obtained using the tracking code PLACET.     

Multipacting phenomenon at high electric fields of superconducting cavities

Recently multipacting (MP) recalculation of the TeV Energy Superconducting Linear Accelerator (TESLA) resonator was performed. In addition to the normal MP which occurs at a peak electric field of around 40MV/m for the TESLA cavity, another type of multipacting with resonant electron trajectory that is far from the equator is also seen.It occurs at a gradient around 60MV/m to 70MV/m. This result seems to explain some experimental observations.     

Seesaw induced Higgs mechanism

We discuss a two scalar doublets model which induces the Higgs mechanism by means of a seesaw mechanism. This model naturally predicts a light Higgs scalar whose mass is suppressed by the grand unification scale. The model requires an intermediate scale between the electroweak symmetry breaking scale and the grand unification scale at 10⁹ GeV. Below this intermediate energy scale the usual standard model appears as an effective theory. An implementation of this mechanism in models where the Planck scale is in the TeV region is discussed. Received: 20 September 2002 / Revised version: 6 March 2003 / Publishes online: 13 May 2003 RID="a" ID="a" e-mail: calmet@theory.caltech.edu     

Main linac lattice design and optimization for Ecm=1 TeV CLIC

The Compact Linear Collider (CLIC) is a future e⁺e^- linear collider. The CLIC study concentrated on a design of center-of-mass energy of 3 TeV and demonstrated the feasibility of the technology. However, the physics also demands lower energy collision. To satisfy this, CLIC can be built in stages. The actual stages will depend on LHC results. Some specific scenarios of staged constructions have been shown in CLIC Concept Design Report (CDR). In this paper, we concentrate on the main linac lattice design for E_cm=1 TeV CLIC aiming to upgrade from E_cm=500 GeV CLIC and then to E_cm=3 TeV one. This main linac accelerates the electron or positron beam from 9 GeV to 500 GeV. A primary lattice design based on the 3 TeV CLIC main linac design and its optimization based on the beam dynamics study will be presented. As we use the same design principles as 3TeV CLIC main linac, this optimization is basically identical to the 3 TeV one. All the simulations results are obtained using the tracking code PLACET.     

Higgs physics with a $\gamma \gamma$ collider based on CLIC 1

We present the machine parameters and physics capabilities of the CLIC Higgs Experiment (CLICHE), a low-energy collider based on CLIC 1, the demonstration project for the higher-energy two-beam accelerator CLIC. CLICHE is conceived as a factory capable of producing around 20,000 light Higgs bosons per year. We discuss the requirements for the CLIC 1 beams and a laser backscattering system capable of producing a total (peak) luminosity of cm^-2s^-1 with GeV. We show how CLICHE could be used to measure accurately the mass, , WW and decays of a light Higgs boson. We illustrate how these measurements may distinguish between the Standard Model Higgs boson and those in supersymmetric and more general two-Higgs-doublet models, complement ing the measurements to be made with other accelerators. We also comment on other prospects in and physics with CLICHE. Received: 20 November 2001 / Published online: 24 March 2003     

Search for top quark FCNC couplings in Z′ models at the LHC and CLIC

The top quark is the heaviest particle to date discovered, with a mass close to the electroweak symmetry breaking scale. It is expected that the top quark would be sensitive to the new physics at the TeV scale. One of the most important aspects of the top quark physics can be the investigation of the possible anomalous couplings. Here, we study the top quark flavor changing neutral current (FCNC) couplings via the extra gauge boson Z′ at the Large Hadron Collider (LHC) and the Compact Linear Collider (CLIC) energies. We calculate the total cross sections for the signal and the corresponding Standard Model (SM) background processes. For an FCNC mixing parameter x=0.2 and the sequential Z′ mass of 1 TeV, we find the single top quark FCNC production cross sections 0.38(1.76) fb at the LHC with $\sqrt{s_{pp}}=7(14)$ TeV, respectively. For the resonance production of sequential Z′ boson and decays to single top quark at the Compact Linear Collider (CLIC) energies, including the initial state radiation and beamstrahlung effects, we find the cross section to be 27.96(0.91) fb at $\sqrt{s_{e^{+}e^{-}}}=1(3)$ TeV, respectively. We make the analysis to investigate the parameter space (mixing-mass) through various Z′ models. It is shown that the results benefit from the flavor tagging.     

Unitarity bounds on low scale quantum gravity

We study the unitarity of models with low scale quantum gravity both in four dimensions and in models with a large extra-dimensional volume. We find that models with low scale quantum gravity have problems with unitarity below the scale at which gravity becomes strong. An important consequence of our work is that their first signal at the Large Hadron Collider would not be of a gravitational nature such as graviton emission or small black holes, but rather would be linked to the mechanism which fixes the unitarity problem. We also study models with scalar fields with non-minimal couplings to the Ricci scalar. We consider the strength of gravity in these models and study the consequences for inflation models with non-minimally coupled scalar fields. We show that a single scalar field with a large non-minimal coupling can lower the Planck mass in the TeV region. In that model, it is possible to lower the scale at which gravity becomes strong down to 14 TeV without violating unitarity below that scale.     

Search for scalar top quark production in p&pmacr; collisions at sqrt

We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb(-1) of p&pmacr; collisions at sqrt[s] = 1.8 TeV. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b-quark jets. For a chargino mass of 90 GeV/c(2) and scalar neutrino masses of at least 40 GeV/c(2), we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios.     

Softening the naturalness problem

It was observed by Veltman a long time ago that a special value for the Higgs boson mass could lead to a cancellation of the quadratically divergent corrections to the Higgs bosons squared mass which appear at one loop. We present a class of low energy models that allow one to soften the naturalness problem in the sense that there can be a cancellation of radiative corrections appearing at one loop. The naturalness problem is shifted from the 1 TeV region to the 10 TeV region. Depending on the specific model under consideration, this scale can even be shifted to a higher energy scale. Signatures of these models are discussed.Received: 11 September 2003, Published online: 12 November 2003     

Search for scalar top and scalar bottom quarks in pp collisions at square root s=1.8 TeV

We have searched for direct pair production of scalar top and scalar bottom quarks in 88 pb-1 of pp collisions at sqrt[s]=1.8 TeV with the CDF detector. We looked for events with a pair of heavy flavor jets and missing energy, consistent with scalar top (bottom) quark decays to a charm (bottom) quark and a neutralino. The numbers of events that pass our selections show no significant deviation from standard model expectations. We compare our results to the next-to-leading order scalar quark production cross sections to exclude regions in scalar quark-neutralino mass parameter space.     

Seesaw mechanism for scalar fields as possible basis for dark energy

We propose a novel mechanism for dark energy, based on an extended seesaw for scalar fields, which does not require any new physics at energies below the TeV scale. A very light quintessence mass is usually considered to be technically unnatural, unless it is protected by some symmetry broken at the new very light scale. We propose that one can use an extended seesaw mechanism to construct technically natural models for very light fields, protected by supersymmetry softly broken above a TeV.     

Heavy charged Higgs boson production at next generation $\gamma\gamma$ colliders

We investigate the scope of all relevant production modes of charged Higgs bosons in the MSSM, with mass larger than the one of the top quark, at future Linear Colliders operating in mode at the TeV energy scale. Final states with one or two bosons are considered, as produced by both tree- and loop-level interactions. Received: 8 November 2002 / Revised version: 12 February 2003 / Published online: 13 May 2003 RID="a" ID="a" e-mail: stefano.moretti@cern.ch RID="b" ID="b" e-mail: kanemu@post.kek.jp     

Investigation of anomalous four-boson couplings in photon-photon collisions at high energies

Anomalous four-boson couplings can be studied in the production of two or three bosons in γγ collisions at high energies. The dependence of the cross section for W ⁺ W ^? production on three anomalous couplings is studied at the TESLA energies (√s～1 TeV). A comprehensive analysis of anomalous contributions to the cross section and angular distributions for the process under consideration is presented.     

Probing little Higgs model in e<Superscript>+</Superscript>e<Superscript>-</Superscript>→νν̄γ process

We study the process e⁺e^-→νν̄γ to search for its sensitivity to the extra gauge bosons Z₂, Z₃ and W₂ ^±, which are suggested by the little Higgs models. We find that the ILC with and CLIC with cover different regions of the LHM parameters. We show that this channel can provide a determination of the parameters, complementary to measurements of the extra gauge bosons obtainable at the upcoming LHC experiments. PACS 14.80.Cp; 12.60.Fr; 12.60.Cn     

Gravity induced particle production in earth’s gravitational field in TeV region

We discuss the production of particles via interaction with the earth’s gravitational field. Explicit calculations are done for high energy scalars passing through earth’s gravitational field. We show for example, that the width for the scalar processφ→3φ can become comparable with a typical weak decay width at an energy scale of a few TeV. (Similar conclusions can be drawn about particles that ultimately couple to some scalar field.) We speculate that similar processes may be responsible for many of the anomalies in the 10–10⁴ TeV experimental data.     

Probing the exotic particle content beyond the standard model

We explore the possible exotic particle content beyond the standard model by examining all its scalar bilinear combinations. We categorize these exotic scalar fields and show that without the suppression of (A) their Yukawa couplings with the known quarks and leptons, and (B) the trilinear couplings among themselves, most are already constrained to be very heavy from the nonobservation of proton decay and neutron-antineutron oscillations, the smallness of , and mixing, as well as the requirement of a nonzero baryon asymmetry of the universe. On the other hand, assumption (B) may be naturally violated in many models, especially in supersymmetry, hence certain exotic scalars are allowed to be below a few TeV in mass and would be easily detectable at planned future hadron colliders. In particular, large cross sections for the distinctive processes like and would be expected at the Fermilab Tevatron and CERN LHC, respectively. Received: 1 September 1998 / Revised version: 15 October 1998 / Published online: 22 March 1999     

Double vector meson production from the BFKL equation

The double vector meson production in two-photon collisions is addressed assuming that the color singlet t-channel exchange carries large momentum transfer. We consider the non-forward solution of the BFKL equation at high energy and large momentum transfer and estimate the total and differential cross section for the process , where V₁ and V₂ can be any two vector mesons ( ). A comparison between our predictions and previous theoretical results obtained at Born level or assuming the pomeron-exchange factorization relations is presented. Our results demonstrate that the BFKL dynamics implies an enhancement of the cross sections. Predictions for the future linear colliders (TESLA, CLIC and ILC) are given. Received: 17 June 2005, Revised: 1 August 2005, Published online: 6 October 2005 PACS: 12.38.Aw, 13.85.Lg, 13.85.Ni     

On the excited quarks and leptons

Using a duality-like finite energy sum rule, we discuss the assumption of having excited fermions at the W scale in a supersymmetric(SUSY) and non-supersymmetric hypercolour theory where quarks and leptons are bound states of fermion and scalar preon constituents. We conclude that a SUSY-like composite model cannot have excited fermions having a mass smaller than 0.5 TeV. A non-SUSY composite model having composite fermions but elementary W bosons can produce an excited fermion mass of the order of M_W provided that the scalar vacuum condensate is of the order of the (TeV)² scale of compositeness.     

Anomalous contributions to 95-195-195-1at high energies

We analyze the processe ⁺ e ^?→e ⁺ e ^? ? ⁺ ? ^? (?=e, μ, τ-leptons) considering several nonstandard contributions in order to search for new physics beyond the standard model. We are able to test compositeness up to the TeV mass scale at LEP II and CLIC energies.     

Unified TeV scale picture of baryogenesis and dark matter

We present a simple extension of the minimal supersymmetric standard model which provides a unified picture of cosmological baryon asymmetry and dark matter. Our model introduces a gauge singlet field N and a color triplet field X which couple to the right-handed quark fields. The out-of-equilibrium decay of the Majorana fermion N mediated by the exchange of the scalar field X generates adequate baryon asymmetry for MN approximately 100 GeV and MX approximately TeV. The scalar partner of N (denoted N1) is naturally the lightest SUSY particle as it has no gauge interactions and plays the role of dark matter. The model is experimentally testable in (i) neutron-antineutron oscillations with a transition time estimated to be around 10(10)sec, (ii) discovery of colored particles X at LHC with mass of order TeV, and (iii) direct dark matter detection with a predicted cross section in the observable range.