Scalar field theory in the strong self-interaction limit

We revisit the monophoton plus missing energy signature at \(e^+e^-\) colliders in supersymmetric (SUSY) models where the gravitino is very light. There are two possible processes which provide the signal: gravitino pair production and associated gravitino production with a neutralino, leading the monophoton final state via an additional photon radiation and via the neutralino decay, respectively. By using the superspace formalism, we construct a model that allows us to study the parameter space for the both processes. We show that the signal cross section and the photon spectra provide information on the masses of the SUSY particles as well as the SUSY breaking scale.     

Can the Higgs be seen in rapidity gap events at the Tevatron or the LHC?

Double diffractive Higgs production at pp (or ) colliders continues to attract attention as a potential signal in the search for the boson. We present improved perturbative QCD estimates of the event rates for both the exclusive and inclusive double diffractive Higgs processes, paying particular attention to the survival probability of the rapidity gaps. We find that the major uncertainty is in the prediction for the survival probability associated with soft rescattering. We show that an analogous process, the double diffractive production of a pair of jets with large values of , has an event rate which makes it accessible at the Tevatron. Observation of this process can therefore be used as a luminosity monitor for two-gluon exchange processes, such as the production of a Higgs boson with rapidity gaps on either side. Received: 8 February 2000 / Published online: 14 April 2000     

Dark matter constraints on gaugino/Higgsino masses in split supersymmetry and their implications at colliders

In split supersymmetry, gauginos and Higgsinos are the only supersymmetric particles that are potentially accessible at soon-to-be-completed colliders. While direct experimental research, such as the LEP and Tevatron experiments, have given robust lower bounds on the masses of these particles, cosmic dark matter can give some upper bounds and thus have important implications for research at future colliders. In this work we scrutinize such dark matter constraints and show the allowed mass range for charginos and neutralinos (the mass eigenstates of gauginos and Higgsinos). We find that the lightest chargino must be lighter than about 1 TeV under the popular assumption M₁=M₂/2 and about 2 or 3 TeV in other cases. The corresponding production rates of the lightest chargino at the CERN large hadron collider (LHC) and the International Linear Collider (ILC) are also given. While in some parts of the allowed region the chargino pair production rate can be larger than 1 pb at the LHC and 100 fb at the ILC, other parts of the region correspond to very small production rates, and thus there is no guarantee of finding the charginos of split supersymmetry at future colliders. PACS 14.80.Ly, 95.35.+d     

Collider signals of unparticle physics

Phenomenology of the notion of an unparticle U, recently perceived by Georgi, to describe a scale invariant sector with a nontrivial infrared fixed point at a higher energy scale is explored in details. Behaving like a collection of d(U) (the scale dimension of the unparticle operator O(U)) invisible massless particles, this unparticle can be unveiled by measurements of various energy distributions for the processes Z-->f f U and e- e+-->gammaU at e- e+ colliders, as well as monojet production at hadron colliders. We also study the propagator effects of the unparticle through the Drell-Yan tree-level process and the one-loop muon anomaly.     

Light dark sector searches at low-energy high-luminosity <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> colliders

Although the standard model (SM) is extremely successful, there are various motivations for considering the physics beyond the SM. For example, the SM includes neither dark energy nor dark matter, which has been confirmed through astrophysical observations. Examination of the dark sector, which contains new, light, weakly-coupled particles at the GeV scale or lower, is well motivated by both theory and dark-matter detection experiments. In this mini-review, we focus on one particular case in which these new particles can interact with SM particles through a kinematic mixing term between U(1) gauge bosons. The magnitude of the mixing can be parameterized by a parameter ?. Following a brief overview of the relevant motivations and the constraints determined from numerous experiments, we focus on the light dark sector phenomenology at low-energy high-luminosity e ⁺ e ^? colliders. These colliders are ideal for probing the new light particles, because of their large production rates and capacity for precise resonance reconstruction. Depending on the details of a given model, the typical observed signatures may also contain multi lepton pairs, displaced vertices, and/or missing energy. Through the use of extremely large data samples from existing experiments, such as KLOE, CLEO, BABAR, Belle, and BESIII, the magnitude of the mixing can be parameterized by a parameter ? < 10^?4–10^?3 constraint can be obtained. Obviously, future experiments with larger datasets will provide opportunities for the discovery of new particles in the dark sector, or for stricter upper limits on ?. Once the light dark sector is confirmed, the particle physics landscape will be changed significantly.     

Exotic hadron bound state production at hadron colliders

The non-relativistic wave function framework is applied to study the production and decay of exotic hadrons, which can be effectively described as bound states of other hadrons. Employing the factorized formulation,with the help of event generators, we investigate the production of exotic hadrons in multiproduction processes at high energy hadron colliders. This study provides crucial information for the measurements of the relevant exotic hadrons.     

Light dark sector searches at low-energy high-luminosity e+e− colliders

Although the standard model (SM) is extremely successful, there are various motivations for considering the physics beyond the SM. For example, the SM includes neither dark energy nor dark matter, which has been confirmed through astrophysical observations. Examination of the dark sector, which contains new, light, weakly-coupled particles at the GeV scale or lower, is well motivated by both theory and dark-matter detection experiments. In this mini-review, we focus on one particular case in which these new particles can interact with SM particles through a kinematic mixing term between U(1) gauge bosons. The magnitude of the mixing can be parameterized by a parameter ϵ. Following a brief overview of the relevant motivations and the constraints determined from numerous experiments, we focus on the light dark sector phenomenology at low-energy high-luminosity e⁺e⁻ colliders. These colliders are ideal for probing the new light particles, because of their large production rates and capacity for precise resonance reconstruction. Depending on the details of a given model, the typical observed signatures may also contain multi lepton pairs, displaced vertices, and/or missing energy. Through the use of extremely large data samples from existing experiments, such as KLOE, CLEO, BABAR, Belle, and BESIII, the ϵ<10⁻⁴–10⁻³ constraint can be obtained. Obviously, future experiments with larger datasets will provide opportunities for the discovery of new particles in the dark sector, or for stricter upper limits on ϵ. Once the light dark sector is confirmed, the particle physics landscape will be changed significantly.     

Associated productions of the new gauge boson BH in the Littlest Higgs model with a SM gauge boson via e+e- collision

With the high energy and luminosity, the planned ILC has the considerable capability to probe the new heavy particles predicted by the new physics models. In this paper, we study the potential to discover the lightest new gauge boson BH of the Littlest Higgs model via the processes e+e- →γ(Z)BH at the ILC. The results show that the production rates of these two processes are large enough to detect BH in a wide range of the parameter spaces, specially for the process e+e- →γBH. Furthermore, there exist some decay modes for BH which can provide the typical signal and clean backgrounds. Therefore, the new gauge boson BH should be observable via these production processes with the running of the ILC if it exist.     

Getting to the top with extra dimensions

The prospect of large extra dimensions and an effective theory of gravity at around a TeV has interesting experimental consequences. In these models, the Kaluza–Klein modes interact with Standard Model particles and these interactions lead to testable predictions at present and planned colliders. We investigate the effect of virtual exchanges of the spin-2 Kaluza–Klein modes in the production cross-section of pairs at the Tevatron and the LHC and find that the cross-section can be an effective probe of the large extra dimensions. This enables us to put bounds on the effective low-energy scale.     

Mass shell technique for measuring masses of a pair of semi-invisibly decaying particles

Motivated by evidence for the existence of dark matter, many new physics models predict the pair production of new particles, followed by the decays into two invisible particles, leading to a momentum imbalance in the visible system. For the cases where all four components of the vector sum of the two "missing" momenta are measured from the momentum imbalance, we present analytic solutions of the final state system in terms of measurable momenta, with the mass shell constraints taken into account. We then introduce new variables which allow the masses involved in the new physics process, including that of the dark matter particles, to be extracted efficiently. These are compared with a selection of variables in the literature, and possible applications at lepton and hadron colliders are discussed.     

The Z′→WW→ℓ+ν+jet+jet signal at hadron colliders

We investigate the prospect of using the lepton-neutrino-jet-jet final state to examine Z′→WW production at high energy hadron colliders. We find that with a judicious selection of events the signal for a new (E₆) gauge boson is comparable to the ordinary QCD background and that, in spite of the small Z′ cross section, detection at a large luminosity super collider might be possible.     

Discovering new physics in the decays of black holes

If the scale of quantum gravity is near a TeV, the CERN Large Hadron Collider (LHC) will be producing one black hole (BH) about every second, thus qualifying as a BH factory. With the Hawking temperature of a few hundred GeV, these rapidly evaporating BHs may produce new, undiscovered particles with masses approximately 100 GeV. The probability of producing a heavy particle in the decay depends on its mass only weakly, in contrast with the exponentially suppressed direct production. Furthermore, backgrounds in the BH sample can be made small. Using the Higgs boson as an example, we show that it may be found at the LHC on the first day of its operation, even with incomplete detectors.     

Catalysis of black holes/wormholes formation in high energy collisions

The current paradigm suggests that BH/WH formation in particles collisions will happen when a center-mass energy of colliding particles is sufficiently above the Planck scale (the transplanckian region). We confirm the classical geometrical cross section of the BH production reconsidering the process of two transplanckian particles collision in the rest frame of one of incident particles. This consideration permits to use the standard Thorne’s hoop conjecture for a matter compressed into a region to prove a variant of the conjecture dealing with a total amount of compressed energy in the case of colliding particles. We briefly mention that the process of BH formation is catalyzed by the negative cosmological constant and by a particular scalar matter, namely dilaton, while it is relaxed by the positive cosmological constant and at a critical value just turns off.     

Signals of excited quarks and leptons

e⁺e^? annihilation to two photons (including beam polarization) and quark-antiquark annihilation to gluons are discussed as possible tools to investigate the existence (and handedness) of excited electrons and quarks. Properties of these particles can also be explored in eγ and ep colliders; production cross sections and the impact of these particles on structure functions are derived.     

Central exclusive particle production at high energy hadron colliders

We review the subject of central exclusive particle production at high energy hadron colliders. In particular, we consider reactions of the type A+B→A+X+B, where X is a fully specified system of particles that is well separated in rapidity from the outgoing beam particles. We focus on the case where the colliding particles are strongly interacting and mainly they will be protons (or antiprotons) as at the ISR, SS, Tevatron and LHC. The data are surveyed and placed within the context of theoretical developments.     

Searching for Top Squark at Hadron Colliders

In this talk we briefly summarise our recent study (hep-ph/0007165) on searching for top squark at hadron colliders. The light top-squark (stop) if produced in hadron colliders in the form of the t1t1 pair and decaying through the likely decay chain t1→X+b followed by X→X0ff′, can mimic closely a top quark event when the mass of the stop is close to that of the top quark. Because of the much lower production rate, the stop event can be buried under the top quark event sample. In order to uncover the stop event, specific selection cuts need to be applied. Through Monte Carlo simulation with suitable kinematic cuts, we found that such stop event can be extracted from the top quark sample and detected by the top counting experiments in the upcoming upgraded Tevatron and LHC. However, because of the small statistics of the Run 1 of the Tevatron, the stop signal remains hidden at Run 1.     

Kinematic cusps: Determining the missing particle mass at colliders

In many extensions of the SM, neutral massive stable particles (dark matter candidates) are produced at colliders in pairs due to an exact symmetry called a “parity”. These particles escape detection, rendering their mass measurement difficult. In the pair production of such particles via a specific (“antler”) decay topology, kinematic cusp structures are present in the invariant mass and angular distributions of the observable particles. Together with the end-points, such cusps can be used to measure the missing particle mass and the intermediate particle mass in the decay chain. Our simulation of a benchmark scenario in a Z^′$Z^{\prime }$ supersymmetric model shows that the cusp feature survives under the consideration of detector simulation and the standard model backgrounds. This technique for determining missing particle masses should be invaluable in the search for new physics at the LHC and future lepton colliders.     

Electron–positron annihilation into three pions and the radiative return

The Monte Carlo event generator PHOKHARA, which simulates hadron and muon production at electron–positron colliders through radiative return, has been extended to final states with three pions. A model for the form factor based on generalized vector dominance has been employed, which is consistent with presently available experimental observations.     

On physics beyond standard model

In this review we do not try to cover all the aspects of physics besnd tile standard model （BSM）, instead our latest understanding on tile BSM will be presented： i） Tile Higgs sector is likely related to BSM, which can be confirmed at current running large hadron collider （LHC） or tile fllture eolliders. Furthermore we pointed out that spontaneous CP violation can be closely related to the lightness of the Higgs boson, ii） Top quark forward-backward asymmetry, which was mea.sured by Tewttron, might be the sign of BSM.2; proposed a new color-octet particle Zcr to account fi）r the observation and Z can be fllrther studied at the LHC. iii） If dark matter （DM） is utilized to accommodate astrophysical obserwtions, it ought to be observed at the high energy LttC and DM produced at colliders should be tile slnoking gun signal, iv） Lithium puzzle might also be the sign of the BSM. We briefly review tile newly proposed solution to Lithium puzzle, i.e.. the existonce of non-thermal component during the big bang nuclei-synthesis （BBN）. The possible origins of the non-thermal coinponent can be dark matter or the new accelerating mechanism of normal particles.