A unique signal of excited bosons in dijet data from <Emphasis Type="Italic">pp</Emphasis> collisions

With this note we would like to draw attention to a possible novel signal of new physics in dijet data at the hadron colliders. Usually it is accepted that almost all exotic models predict that these two jets populate the central (pseudo)rapidity region where y _1,2 ≅ 0. Contrary, the excited bosons do not contribute into this region, but produce an excess of dijet events over the almost flat QCD background in χ = exp|y ₁−y ₂| away from this region. For the special choice of parameters this could lead to a dip in the centrality ratio distribution over the dijet invariant mass instead of a bump, expected for the most exotic models.     

Neutral-meson production in <Emphasis Type="Italic">pp</Emphasis> collisions at RHIC and QCD test of <Emphasis Type="Italic">z</Emphasis> scaling

New experimental data on inclusive cross section of neutral-vector-meson (ω ⁰, ϕ, K _S ⁰) production in proton-proton collisions at = 200 GeV obtained at RHIC are analyzed in the framework of z scaling. Properties of z-presentation are used to predict hadron yields over a wide range of transverse momentum p _T and collisions energy . The next-to-leading-order perturbative QCD calculations of inclusive cross sections of π ⁰ mesons produced in pp and collisions over a wide range of and p _T are compared with ISR, S pS, RHIC data and predictions of z scaling. The dependence of the spectra in p _T and z presentations for different parton distribution and fragmentation functions is studied. The sensitivity of the obtained results to the choice of the renormalization (μ _R ), initial-state factorization (μ _F ), and final-state factorization (fragmentation) (μ _H ) scales is verified. It is shown that self-similar features of particle production dictated by the z scaling give strong restriction on the asymptotic behavior of the inclusive spectra in high-p _T region. The text was submitted by the author in English.     

Observables for possible QGP signatures in central <Emphasis Type="Italic">pp</Emphasis> collisions

Proton–proton (pp) data show collective effects, such as long-range azimuthal correlations and strangeness enhancement, which are similar to phenomenology observed in heavy ion collisions. Using simulations with and without explicit existing models of collective effects, we explore new ways to probe pp collisions at high multiplicity, in order to suggest measurements that could help identify the similarities and differences between large- and small-scale collective effects. In particular, we focus on the properties of jets produced in ultra-central pp collisions in association with a Z boson. We consider observables such as jet energy loss and jet shapes, which could point to the possible existence of an underlying quark-gluon plasma, or other new dynamical effects related to the presence of large hadronic densities.     

Corona effect in <Emphasis Type="Italic">AA</Emphasis> collisions at the LHC

Following our earlier finding based on RHIC data on the dominant jet production from nucleus corona region, we reconsider this effect in nucleus–nucleus collisions at the LHC energies. Our hypothesis was based on experimental data, which raised the idea of a finite formation time for the produced medium. At the RHIC energy and in low-density corona region, this time reaches about 2 fm/c. Following this hypothesis, the nuclear modification factor R _AA at high p _t should be independent on particle momentum, and the azimuthal anisotropy of high p _t particles, v ₂, should be finite. A separate prediction held that, at the LHC energy, the formation time in the corona region should be about 1 fm/c. New LHC data show that R _AA is not flat and is rising with p _t . We add to our original hypothesis an assumption that a fast parton traversing the produced medium loses the fixed portion of its energy. A shift of about 7 GeV from the original power law p ^?6 production cross section in pp explains well all the observed R _AA dependencies. The shift of about 7 GeV is also valid at the RHIC energy. We also show that the observed at the LHC dependence of v ₂ at high p _t and our previous predictions agree.     

Heavy-flavor production in <Emphasis Type="Italic">pp</Emphasis> and heavy-ion collisions in QCD up-to-LHC energies

Charm production in pp collisions is considered in the framework of perturbative QCD. The values of two parameters, the charm quark mass m _c and the QCD scale μ², are determined from the comparison of the theoretical calculations with experimental data. The RHIC data on charm and beauty production are compared with the k _T -factorization approach predictions and with standard NLO QCD. The calculated results underestimate the STAR Collaboration data. The role of possible nuclear effects is discussed. The predictions for LHC energies are also given.     

Scaling of semi-inclusive events in <Emphasis Type="Italic">pp</Emphasis> interactions

The normalized single-particle semi-inclusive double-differential spectrum of π^t- mesons from pp interactions at 6.6–400 GeV/c and the relative concentration of π⁰ and K _S ⁰ mesons in such events of fixed multiplicity of π^? mesons are completely determined by specifying any feature of this spectrum—for example, 〈y²〉 _n or 〈E〉 _n . Therefore, a two-parameter sample of semi-inclusive events that depends on the energy and the multiplicity reduces to a one-parameter sample.     

<Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) Cosmology from <Emphasis Type="Italic">q</Emphasis>-theory

From a macroscopic theory of the quantum vacuum in terms of conserved relativistic charges (generically denoted by q ^(a) with label a), we have obtained, in the low-energy limit, a particular type of f(R) model relevant to cosmology. The macroscopic quantum-vacuum theory allows us to distinguish between different phenomenological f(R) models on physical grounds. The text was submitted by the authors in English.     

Energy dependence of Cronin momentum in saturation model for <Emphasis Type="Italic">p</Emphasis> + <Emphasis Type="Italic">A</Emphasis> and <Emphasis Type="Italic">A</Emphasis> + <Emphasis Type="Italic">A</Emphasis> collisions

The energy dependence of the Cronin momentum for p + A and A + A collisions in the saturation model are calculated. This dependence is consistent with simple dimensional considerations and can be used to test the validity of the saturation model. It gives the possibility to distinguish the different variants of the saturation model with precise experimental data and to measure the x dependence of the saturation momentum.     

<Emphasis Type="Italic">B</Emphasis> decays into light scalar particles and glueball

The recent observations of f ₀(980) in charmless B decays motivate further studies of scalar particle and glueball production in these processes. Amplitudes for charmless two-body B decays involving the members of the scalar nonet are presented based on the symmetries of the dominant penguin contribution. Different scenarios for the lightest scalar nonet are investigated in view of the presently available data. We describe the evidence from B decays for f ₀(1500) with a flavor octet like mixing and the hints towards the members of the nonet of lowest mass. There is further support for the hypothesis of a broad 0 ^{+ +} glueball acting as coherent background especially in . The estimated B decay rates into gluonic mesons represent a sizable fraction of the theoretically derived decay rate for .Received: 23 April 2004, Revised: 27 October 2004, Published online: 21 December 2004Work supported in part by the Schweizerischer Nationalfonds.     

Non-vacuum Bianchi types <Emphasis Type="Italic">I</Emphasis> and <Emphasis Type="Italic">V</Emphasis> in <Emphasis Type="Italic">f</Emphasis> (<Emphasis Type="Italic">R</Emphasis>) gravity

In a recent paper (Sharif and Shamir in Class. Quantum Grav. 26:235020, 2009), we have studied the vacuum solutions of Bianchi types I and V spacetimes in the framework of metric f (R) gravity. Here we extend this work to perfect fluid solutions. For this purpose, we take stiff matter to find energy density and pressure of the universe. In particular, we find two exact solutions in each case which correspond to two models of the universe. The first solution gives a singular model while the second solution provides a non-singular model. The physical behavior of these models has been discussed using some physical quantities. Also, the function of the Ricci scalar is evaluated.     

<Emphasis Type="Italic">z</Emphasis>-Scaling and high-<Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> particle production in hadron-hadron and hadron-nucleus collisions at high energies

The general features of particle production in hadron-hadron and hadron-nucleus collisions at high energy and transverse momentum using the concept of z-scaling are reviewed. z-Presentation of experimental data on the inclusive cross sections obtained at ISR, SPS, and Tevatron is presented and its properties are discussed. It is argued that the properties reflect the fundamental symmetries such as self-similarity, locality, and fractality. z-Scaling is used to predict particle yields in hadron-hadron and hadron-nucleus collisions at RHIC and LHC energies. The violation of z-scaling is considered as a signature of new physics phenomena.     

Ferromagnetism and ferroelectricity in Eu<Emphasis Type="Italic">X</Emphasis> (<Emphasis Type="Italic">X</Emphasis> = <Emphasis Type="Italic">O</Emphasis>, <Emphasis Type="Italic">S</Emphasis>): pressure effects

Ferromagnetism and ferroelectricity in Eu monochalcogenides have been investigated by ab initio density functional theory in the DFT+U approach. Exchange interaction parameters and Curie temperatures under pressure are studied and discussed using Heisenberg Hamiltonian with first and second-nearest-neighbor interactions. The calculations showed that the hydrostatic pressure perfectly improves the Curie temperature (EuO: T _C = 175 K; EuS: T _C = 33.8 K) and in the other hand it cannot induce the spontaneous polarization (P _s ). The effect of uniaxial and biaxial pressure is also studied. Although the uniaxial strains slightly increases the Curie temperature, it ensures the ferrolectricity in these systems by producing a spontaneous polarization of the order of P _s (EuO) = 57.50 μC/cm² and P _s (EuS) = 42.86 μC/cm² with pressures of 5% and 4%, respectively. The search for new model systems is a necessity to better understand the physics related to multiferroïc materials and to consider possible applications.     

Production and correlations of <Emphasis Type="Italic">b</Emphasis> quarks at the LHC energies

Processes leading to b-quark production at the LHC energies are simulated by using the Pythia generator. For proton-proton interactions at 7 and 14 TeV, the cross sections for b-quark production are evaluated for three mechanisms that are taken into account in the Pythia generator. These are quark-pair production, the excitation of sea quarks, and gluon splitting. Correlations of azimuthal angles of b-quark emission and properties of accompanying particles in events induced by the various mechanisms of b-quark production are calculated. The results are compared with data from the CDF experiment.     

Production of secondaries in high-energy <Emphasis Type="Italic">d</Emphasis>+Au collisions

In the framework of the quark–gluon string model we calculate the inclusive spectra of secondaries produced in d+Au collisions at intermediate (CERN SPS) and at much higher (RHIC) energies. The results of numerical calculations at intermediate energies are in reasonable agreement with the data. At RHIC energies numerically large inelastic screening corrections (percolation effects) should be accounted for in the calculations. We extract these effects from the existing experimental data of RHIC on minimum-bias and central d+Au collisions. The predictions for p+Au interactions at LHC energy are also given.     

<Emphasis Type="Italic">Z</Emphasis> lineshape versus fourth-generation masses

The dependence of the Z-resonance shape on the location of the threshold of the N\(\bar N\) production (N is the fourth-generation neutrino) is analyzed. The bounds on the existence of the fourth generation are derived from the comparison of the theoretical expression for the Z lineshape with the experimental data. The fourth generation is excluded at 95% C.L. for m _N <46.7±0.2 GeV.     

Reconstruction of some cosmological models in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>,<Emphasis Type="Italic">T</Emphasis>) cosmology

In this paper, we reconstruct cosmological models in the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the stress-energy tensor. We show that the dust fluid reproduces ΛCDM, phantom–non-phantom era and phantom cosmology. Further, we reconstruct different cosmological models, including the Chaplygin gas, and scalar field with some specific forms of f(R,T). Our numerical simulation for the Hubble parameter shows good agreement with the BAO observational data for low redshifts, z<2.     

Accelerating universe from <Emphasis Type="Italic">F</Emphasis>(<Emphasis Type="Italic">T</Emphasis>) gravity

It is shown that the acceleration of the universe can be understood by considering a F(T) gravity models. For these F(T) gravity models, a variant of the accelerating cosmology reconstruction program is developed. Some explicit examples of F(T) are reconstructed from the background FRW expansion history.     

Jet production in <Emphasis Type="Italic">pA</Emphasis> and <Emphasis Type="Italic">AA</Emphasis> collisions in the perturbative QCD pomeron model

Inclusive cross-sections for gluon jet production are studied numerically in the perturbative QCD pomeron model for pA and central AA collisions at high energies. Two forms for the inclusive cross-sections, with and without emission from the triple pomeron vertex, are compared. The difference was found to reduce to a numerical factor for momenta below the saturation momentum Q _s. Above Q _s no difference was found at all. For pA collisions the gluon spectrum was found to be at momenta k below Q _s and above it. For central AA collisions it was found to be at momenta k below Q _s and above it. At large k the spectrum goes like , flattening with energy. The multiplicities turned out to be proportional to A ^0.7 for pA collisions and A for central AA collisions with a good precision. In the latter case they are becoming more peaked at the center with the growth of energy. Their absolute values are high and grow rapidly with energy in accordance with the high value of the BFKL intercept.Received: 12 October 2004, Revised: 22 November 2004, Published online: 21 January 2005