Heavy neutral gauge bosons at the LHC in an extended MSSM

Searching for heavy neutral gauge bosons Z^′$Z^{\prime }$, predicted in extensions of the Standard Model based on a U(1)^′$\mathrm{U}{(1)}^{\prime }$ gauge symmetry, is one of the challenging objectives of the experiments carried out at the Large Hadron Collider. In this paper, we study Z^′$Z^{\prime }$ phenomenology at hadron colliders according to several U(1)^′$\mathrm{U}{(1)}^{\prime }$-based models and in the Sequential Standard Model. In particular, possible Z^′$Z^{\prime }$ decays into supersymmetric particles are included, in addition to the Standard Model modes so far investigated. We point out the impact of the U(1)^′$\mathrm{U}{(1)}^{\prime }$ group on the MSSM spectrum and, for a better understanding, we consider a few benchmarks points in the parameter space. We account for the D-term contribution, due to the breaking of U(1)^′$\mathrm{U}{(1)}^{\prime }$, to slepton and squark masses and investigate its effect on Z^′$Z^{\prime }$ decays into sfermions. Results on branching ratios and cross sections are presented, as a function of the MSSM and U(1)^′$\mathrm{U}{(1)}^{\prime }$ parameters, which are varied within suitable ranges. We pay special attention to final states with leptons and missing energy and make predictions on the number of events with sparticle production in Z^′$Z^{\prime }$ decays, for a few values of integrated luminosity and centre-of-mass energy of the LHC.     

Searching for an extra neutral gauge boson from muon pair production at LHC

We search for signatures of the extra neutral gauge boson Z^′$Z^{\prime }$, predicted in some extensions of the Standard Model, from the analysis of some distributions for p+p→μ⁺+μ⁻+X$p+p\to {\mu }^{+}+{\mu }^{-}+X$, where the only exotic particle involved is Z^′$Z^{\prime }$. In addition to the invariant mass and charge asymmetry distributions, we propose in our search to use the transverse momentum distribution (pT$p_T$) as an observable. We do our calculation for two values of the LHC center of mass energy (7 and 14 TeV), corresponding to 1 and 100 fb⁻¹ of luminosity, in order to compare our findings from some models with the distributions following from the Standard Model. By applying convenient cuts in the invariant mass, we show that the final particles pT$p_T$ distributions can reveal the presence of an extra neutral gauge boson contribution. We also claim that it is possible to disentangle the models considered here and we emphasize that the minimal version of the model, based on SUC₍₃₎×SUL₍₃₎×UX₍₁₎$\mathit{SU}{(3)}_C\times \mathit{SU}{(3)}_L\times U{(1)}_X$ symmetry, presents the more clear signatures for Z^′$Z^{\prime }$ existence.     

Anisotropic in-plane misfit strains dependence of phase diagrams and dielectric behavior in epitaxial Pb(Zr1−xTix)O3 thin films

A phenomenological Landau–Devonshire thermodynamic theory is used to describe the effects of anisotropic in-plane misfit strains on equilibrium polarization states and dielectric properties of single domain epitaxial Pb(Zr_1−xTi_x)O₃ thin films grown on dissimilar orthorhombic substrates. Compared with the “isotropic in-plane misfit strains-temperature” phase diagrams, the characteristic features of “misfit strain-misfit strain” and “misfit strain-temperature” phase diagrams under the circumstance of strain anisotropy are the presence of four different phases (a^′$a^{\prime }$, a^″$a^{″}$, a^′c$a^{\prime }c$, and a^″c$a^{″}c$) and the direct 90° polarization switching between c   phase and a^′$a^{\prime }$ phase (or a^″$a^{″}$ phase), between a^′$a^{\prime }$ phase and a^″$a^{″}$ phase. The misfit strain dependence of polarization components, the small-signal dielectric responses and the tunabilities at room temperature are also calculated. We find that the phase diagrams and dielectric properties largely depend on anisotropic in-plane misfit strains as well. Moreover, the strain anisotropy will lead to the polarization and dielectric anisotropy.     

Atomic parity violation in the economical 3–3–1 model

The deviation δQW$\delta Q_{\mathrm{W}}$ of the weak charge from its standard model prediction due to the mixing of the W boson with the charged bilepton Y as well as of the Z   boson with the neutral Z^′$Z^{\prime }$ and the real part of the non-Hermitian neutral bilepton X   in the economical 3–3–1 model is established. Additional contributions to the usual δQW$\delta Q_{\mathrm{W}}$ expression in the extra U(1)$\mathrm{U}(1)$ models and the left–right models are obtained. Our calculations are quite different from previous analyzes in this kind of the 3–3–1 models and give the limit on mass of the Z^′$Z^{\prime }$ boson, the Z–Z^′$Z\text{–}{Z}^{\prime }$ and W–Y$W\text{–}Y$ mixing angles with the more appropriate values: MZ^′>564 GeV$M_{Z^{\prime }}>564\text{GeV}$, −0.018<sinφ<0$-0.018<\sin \phi <0$ and |sinθ|<0.043$|\sin \theta |<0.043$.     

Supermodels for early LHC

We investigate which new physics signatures could be discovered in the first year of the LHC, beyond the expected sensitivity of the Tevatron data by the end of 2010. We construct “supermodels”, for which the LHC sensitivity even with only 10 pb⁻¹ useful luminosity is greater than that of the Tevatron with 10 fb⁻¹. The simplest supermodels involve s  -channel resonances in the quark–antiquark and especially in the quark–quark channels. We concentrate on easily visible final states with small standard model backgrounds, and find that there are simple searches, besides those for Z^′$Z^{\prime }$ states, which could discover new physics in early LHC data. Many of these are well-suited to test searches for “more conventional” models, often discussed for multi-fb⁻¹ data sets.     

Determining spin through quantum azimuthal-angle correlations

Determining the spin of new particles is critical in identifying the true theory among various extensions of the Standard Model at the next generation of colliders. Quantum interference between different helicity amplitudes was shown to be effective when the final state is fully reconstructible. However, many interesting new physics processes allow only for partial reconstruction. In this Letter, we show how the interference effect can be unambiguously extracted even in processes that have two-fold ambiguity, by considering the correlation between two decay planes in e⁺e⁻$e^{+}{e}^{-}$ collisions.     

QCD as a topologically ordered system

We argue that QCD belongs to a topologically ordered phase similar to many well-known condensed matter systems with a gap such as topological insulators or superconductors. Our arguments are based on an analysis of the so-called “deformed QCD” which is a weakly coupled gauge theory, but nevertheless preserves all the crucial elements of strongly interacting QCD, including confinement, nontrivial θ$\theta$ dependence, degeneracy of the topological sectors, etc. Specifically, we construct the so-called topological “BF” action which reproduces the well known infrared features of the theory such as non-dispersive contribution to the topological susceptibility which cannot be associated with any propagating degrees of freedom. Furthermore, we interpret the well known resolution of the celebrated U(1)_A$U{\left(1\right)}_A$ problem where the would be η^′${\eta }^{\prime }$ Goldstone boson generates its mass as a result of mixing of the Goldstone field with a topological auxiliary field characterizing the system. We then identify the non-propagating auxiliary topological field of the BF formulation in deformed QCD with the Veneziano ghost (which plays the crucial role in resolution of the U(1)_A$U{\left(1\right)}_A$ problem). Finally, we elaborate on relation between “string-net” condensation in topologically ordered condensed matter systems and long range coherent configurations, the “skeletons”, studied in QCD lattice simulations.     

Electroweak chiral Lagrangian for a hypercharge-universal topcolor model

Electroweak chiral Lagrangian for a hypercharge-universal topcolor model is investigated. We find that the assignments of universal hypercharge improve the results obtained previously from K. Lane's prototype natural TC2 model by allowing a larger Z^′$Z^{\prime }$ mass resulting in a very small T parameter and the S parameter is still around the order of +1.     

On climbing scalars in String Theory

In string models with “brane supersymmetry breaking” exponential potentials emerge at (closed-string) tree level but are not accompanied by tachyons. Potentials of this type have long been a source of embarrassment in flat space, but can have interesting implications for Cosmology. For instance, in ten dimensions the logarithmic slope |V^′/V|$|V^{\prime }/V|$ lies precisely at a “critical” value where the Lucchin–Matarrese attractor disappears while the scalar field is forced to climb up the potential when it emerges from the Big Bang. This type of behavior is in principle perturbative in the string coupling, persists after compactification, could have trapped scalar fields inside potential wells as a result of the cosmological evolution and could have also injected the inflationary phase of our Universe.     

U-boson and the HyperCP exotic events

We show that the very light spin-1 gauge U-boson of the extra U(1)^′$U{(1)}^{\prime }$ gauge model in the framework of the supersymmetric Standard Model extension can be a good candidate of the new light particle suggested by the HyperCP experiment. We demonstrate that the flavor changing neutral currents (FCNCs) for the HyperCP events in the decay of Σ⁺→pμ⁺μ⁻${\Sigma }^{+}\to p{\mu }^{+}{\mu }^{-}$ can be generated at both tree and loop levels. In particular, we find that the loop induced s→dU$s\to dU$ transition due to the tensor-type interaction with the dimension-5 electric dipole operator plays a very important role on the FCNCs. Our explanation of the HyperCP data with the spin-1 U-boson is different from that based on a light pseudoscalar Higgs boson or sgoldstino in the literature. In particular, the U-boson involves a rich phenomenology in particle physics as well as cosmology.     

NNLO benchmarks for gauge and Higgs boson production at TeV hadron colliders

The inclusive production cross sections for W⁺,W⁻$W^{+},W^{-}$ and Z⁰$Z^0$-bosons form important benchmarks for the physics at hadron colliders. We perform a detailed comparison of the predictions for these standard candles based on recent next-to-next-to-leading order (NNLO) parton parameterizations and new analyses including the combined HERA data, compare to all available experimental results, and discuss the predictions for present and upcoming RHIC, SPS, Tevatron and LHC energies. The rates for gauge boson production at the LHC can be rather confidently predicted with an accuracy of better than about 10% at NNLO. We also present detailed NNLO predictions for the Higgs boson production cross sections for Tevatron and LHC energies (1.96, 7, 8, 14 TeV), and propose a possible method to monitor the gluon distribution experimentally in the kinematic region close to the mass range expected for the Higgs boson. The production cross sections of the Higgs boson at the LHC are presently predicted with an accuracy of about 10–17%. The inclusion of the NNLO contributions is mandatory for achieving such accuracies since the total uncertainties are substantially larger at NLO.     

A note on embedding non-Abelian finite flavor groups in continuous groups

A non-Abelian finite flavor group G⊂SO(3)$G\subset \mathit{SO}(3)$ can have double covering G^′⊂SU(2)$G^{\prime }\subset \mathit{SU}(2)$ such that G⊄G^′$G\not\subset G^{\prime }$. This situation is not contradictory, but quite natural, and we give explicit examples such as G=Dn$G=D_n$, G^′=Q_2n$G^{\prime }=Q_{2n}$ and G=T$G=T$, G^′=T^′$G^{\prime }=T^{\prime }$. This observation can be crucial in particle theory model building.     

Unparticle physics with broken scale invariance

If scale invariance is exact, unparticles are unlikely to be probed in colliders since there are stringent constraints from astrophysics and cosmology. However these constraints are inapplicable if scale invariance is broken at a scale μ?1 GeV$\mu ?1\text{GeV}$. The case 1 GeV?μ<MZ$1\text{GeV}?\mu <M_Z$ is particularly interesting since it allows unparticles to be probed at and below the Z pole. We show that μ   can naturally be in this range if only vector unparticles exist, and briefly remark on implications for Higgs phenomenology. We then obtain constraints on unparticle parameters from e⁺e⁻→μ⁺μ⁻$e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ cross-section and forward–backward asymmetry data, and compare with the constraints from mono-photon production and the Z hadronic width.     

On search for eV hidden-sector photons in Super-Kamiokande and CAST experiments

If light hidden sector photons (γ^′${\gamma }^{\prime }$s) exist, they could be produced through kinetic mixing with solar photons in the eV energy range. We propose to search for this hypothetical γ^′${\gamma }^{\prime }$-flux with the Super-Kamiokande and/or upgraded CAST detectors. The proposed experiments are sensitive to the γ–γ^′$\gamma \text{–}{\gamma }^{\prime }$ mixing strength as small as ¹⁰⁻⁵?χ?¹⁰⁻⁹${10}^{\mathrm{-5}}?\chi ?{10}^{\mathrm{-9}}$ for the γ^′${\gamma }^{\prime }$ mass region ¹⁰⁻⁴?mγ^′?¹⁰⁻¹ eV${10}^{\mathrm{-4}}?m_{{\gamma }^{\prime }}?{10}^{\mathrm{-1}}\text{eV}$ and, in the case of non-observation, would improve limits recently obtained from photon regeneration laser experiments for this mass region.     

A light scalar in low-scale technicolor

In addition to the narrow spin-one resonances ρT${\rho }_T$, ωT${\omega }_T$ and aT$a_T$ occurring in low-scale technicolor, there will be relatively narrow scalars in the mass range 200 to 600–700 GeV. We study the lightest isoscalar state, σT${\sigma }_T$. In several important respects it is like a heavy Higgs boson with a small vev. It may be discoverable with high luminosity at the LHC where it is produced via weak boson fusion and likely has substantial W⁺W⁻$W^{+}{W}^{-}$ and Z⁰Z⁰$Z^0{Z}^0$ decay modes.     

Galactic neutrino communication

We examine the possibility to employ neutrinos to communicate within the galaxy. We discuss various issues associated with transmission and reception, and suggest that the resonant neutrino energy near 6.3 PeV may be most appropriate. In one scheme we propose to make Zo$Z^o$ particles in an overtaking e⁺−e⁻$e^{+}-e^{-}$ collider such that the resulting decay neutrinos are near the W⁻$W^{-}$ resonance on electrons in the laboratory. Information is encoded via time structure of the beam. In another scheme we propose to use a 30 PeV pion accelerator to create neutrino or anti-neutrino beams. The latter encodes information via the beam CP state as well as timing. Moreover the latter beam requires far less power, and can be accomplished with presently foreseeable technology. Such signals from an advanced civilization, should they exist, will be eminently detectable in existing neutrino detectors.