arXiv subjects

K. Tuominen

Publications and source records attributed to K. Tuominen.

35 records · Page 2Linked to original sources

arXiv2005

Light Composite Higgs from Higher Representations versus Electroweak Precision Measurements -- Predictions for LHC

We investigate theories in which the technifermions in higher dimensional representations of the technicolor gauge group dynamically break the electroweak symmetry of the standard model. For the two-index symmetric representation of the gauge group the lowest number of techniflavors needed to render the underlying gauge theory quasi conformal is two. We confront the models with the recent electroweak precision measurements and demonstrate that the two technicolor theory is a valid candidate for a dynamical breaking of the electroweak symmetry. The electroweak precision measurements provide useful constraints on the relative mass splitting of the new leptons needed to cure the Witten anomaly. In the case of a fourth family of leptons with ordinary lepton hypercharge the new heavy neutrino can be a natural candidate of cold dark matter. We also propose theories in which the critical number of flavors needed to enter the conformal window is higher than the one with fermions in the two-index symmetric representation, but lower than in the walking technicolor theories with fermions only in the fundamental representation of the gauge group. Due to the near conformal/chiral phase transition, we show that the composite Higgs is very light compared to the intrinsic scale of the technicolor theory. For the two technicolor theory we predict the composite Higgs mass not to exceed 150 GeV.

hep-ph↗

arXiv2004

Deconfinement and Chiral Symmetry: Competing Orders

We investigate the interplay between chiral symmetry restoration and deconfinement both in two color QCD and adjoint QCD. In ordinary QCD we show how the behavior of the Polyakov loop near chiral phase transition is induced by the chiral order parameter, while in adjoint two color QCD one has two truly independent phase transitions. Introducing a finite baryochemical potential we find that adjoint QCD exhibits tetracritical behavior.

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arXiv2004

Subprocess Size in Hard Exclusive Scattering

The interaction region of hard exclusive hadron scattering can have a large transverse size due to endpoint contributions, where one parton carries most of the hadron momentum. The endpoint region is enhanced and can dominate in processes involving multiple scattering and quark helicity flip. The endpoint Fock states have perturbatively short lifetimes and scatter softly in the target. We give plausible arguments that endpoint contributions can explain the apparent absence of color transparency in fixed angle exclusive scattering and the dimensional scaling of transverse rho photoproduction at high momentum transfer, which requires quark helicity flip. We also present a quantitative estimate of Sudakov effects.

hep-ph↗

arXiv2004

Confinement and Chiral Symmetry

We illustrate why color deconfines when chiral symmetry is restored in gauge theories with quarks in the fundamental representation, and while these transitions do not need to coincide when quarks are in the adjoint representation, entanglement between them is still present.

hep-ph↗

arXiv2003

Connecting Polyakov Loops to Hadrons

The order parameter for the pure Yang-Mills phase transition is the Polyakov loop, which encodes the symmetries of the Z_N center of the SU(N) gauge group. The physical degrees of freedom of any asymptotically free gauge theory are hadronic states. Using the Yang-Mills trace anomaly and the exact Z_N symmetry we show that the transfer of information from the order parameter to hadrons is complete.

hep-ph↗

arXiv2002

Dynamics of Particle Production in Relativistic Nuclear Collisions

Saturation models for particle production in relativistic nuclear collisions are discussed. In particular, I show that the predictions from the high density QCD for the qualitative shape of $dN/dy$ are very sensitive to the form of the unintegrated gluon distribution.

hep-ph↗

arXiv2002

Saturation and Pion Production in Proton-Nucleus Collisions

We study the effects of gluon saturation on pion production in high energy proton-nucleus collisions using the color glass condensate model. At high p_perp, we show that the p_perp-distribution of gluons behaves as ~ 1/(p_perp^7) in accordance with both conventional perturbative QCD calculations and experiment. Fragmentation of gluons into pions leads to a rapidity dependent depletion of pions relative to the conventional perturbative QCD predictions. We argue that these clear and systematic differences provide a signal for the onset of gluon saturation which is accessible in upcoming experiments.

hep-ph↗

arXiv2002

Rapidity dependence of particle production in ultrarelativistic nuclear collisions

We compute the rapidity dependence of particle and transverse energy production in ultrarelativistic heavy ion collisions at various beam energies and atomic numbers using the perturbative QCD + saturation model. The distribution is a broad gaussian near $y=0$ but the rapid increase of particle production with the beam energy will via energy conservation strongly constrain the rapidity distribution at large $y$.

hep-ph↗

arXiv2001

Heavy ion collision multiplicities and gluon distribution functions

Atomic number ($A$) and energy ($\roots$) scaling exponents of multiplicity and transverse energy in heavy ion collisions are analytically derived in the perturbative QCD + saturation model. The exponents depend on the small-$x$ behaviour of gluon distribution functions at an $x$-dependent scale. The relation between initial state and final state saturation is also discussed.

hep-ph↗

arXiv2001

Multiplicities and Transverse Energies in Central AA Collisions at RHIC and LHC from pQCD, Saturation and Hydrodynamics

We compute the particle multiplicities and transverse energies at central and nearly central AA collisions at RHIC and LHC. The initial state is computed from perturbative QCD supplemented by the conjecture of saturation of produced partons. The expansion stage is described in terms of hydrodynamics assuming longitudinal boost invariance and azimuthal symmetry. Transverse flow effects, a realistic list of hadrons and resonance decays are included. Comparison with the data of the multiplicities at $\sqrt s=56$ AGeV and 130 AGeV from RHIC is done and predictions for the full RHIC energy and LHC energy are made for the multiplicities and transverse energies. The reduction from the initially released minijet transverse energy to the $E_T$ in the final state is less than in the one-dimensional case but still dramatic: a factor of 2.7 at RHIC, and 3.6 at the LHC.

hep-ph↗

arXiv2001

Centrality dependence of multiplicity, transverse energy, and elliptic flow from hydrodynamics

The centrality dependence of the charged multiplicity, transverse energy, and elliptic flow coefficient is studied in a hydrodynamic model, using a variety of different initializations which model the initial energy or entropy production process as a hard or soft process, respectively. While the charged multiplicity depends strongly on the chosen initialization, the p_t-integrated elliptic flow for charged particles as a function of charged particle multiplicity and the p_t-differential elliptic flow for charged particles in minimum bias events turn out to be almost independent of the initial energy density profile.

hep-ph↗

arXiv2000

Transverse energy from minijets in ultrarelativistic nuclear collisions: a next-to-leading order analysis

We compute in next-to-leading order (NLO) perturbative QCD the amount of transverse energy produced into a rapidity region $ΔY$ of a nuclear collision from partons created in the few-GeV subcollisions. The NLO formulation assumes collinear factorization and is based on the subtraction method. We first study the results as a function of the minimum transverse momentum scale and define and determine the associated $K$-factors. The dependence of the NLO results on the scale choice and on the size of $ΔY$ is also studied. The calculations are performed for GRV94 and CTEQ5 sets of parton distributions. Also the effect of nuclear shadowing to the NLO results is investigated. The main results are that the NLO results are stable relative to the leading-order (LO) ones even in the few-GeV domain and that there exists a new kinematical region not present in the LO, which is responsible for the magnitude of the $K$-factors. The dependence on the size of $ΔY$ is found to be practically linear within two central units of rapidity, and the scale dependence present at RHIC energies is seen to vanish at the LHC energies. Finally, the effect of NLO corrections to the determination of transverse energies and multiplicities in nuclear collisions is discussed within the framework of parton saturation.

hep-ph↗

arXiv2000

Centrality dependence of multiplicities in ultrarelativistic nuclear collisions

We compute the centrality dependence of multiplicities of particles produced in ultrarelativistic nuclear collisions at various energies and atomic numbers. The computation is carried out in perturbative QCD with saturated densities of produced gluons and by including effects of nuclear geometry. Numbers are given for Au+Au collisions at RHIC energies.

hep-ph↗

arXiv2000

Results from pQCD for A+A collisions at RHIC & LHC energies

This talk will discuss how to compute initial quantites in heavy ion collisions at RHIC (200 AGeV) and at LHC (5500 AGeV) using perturbative QCD (pQCD) by including the next-to-leading order (NLO) corrections and a dynamical determination of the dominant physical scale. The initial numbers are converted into final ones by assuming kinetic thermalization and adiabatic expansion.

hep-ph↗

arXiv2000

Production of transverse energy from minijets in next-to-leading order perturbative QCD

We compute in next-to-leading order (NLO) perturbative QCD the transverse energy carried into the central rapidity unit of hadron or nuclear collisions by the partons freed in the few-GeV subcollisions. The formulation is based on a rapidity window and a measurement function of a new type. The behaviour of the NLO results as a function of the minimum transverse momentum and as a function of the scale choice is studied. The NLO results are found to be stable relative to the leading-order ones even in the few-GeV domain.

hep-ph↗

arXiv1999

Scaling of transverse energies and multiplicities with atomic number and energy in ultrarelativistic nuclear collisions

We compute how the initial energy density and produced gluon, quark and antiquark numbers scale with atomic number and beam energy in ultrarelativistic heavy ion collisions. The computation is based on the argument that the effect of all momentum scales can be estimated by performing the computation at one transverse momentum scale, the saturation momentum. The initial numbers are converted to final ones by assuming kinetic thermalisation and adiabatic expansion. The main emphasis of the study is at LHC and RHIC energies but it is observed that even at SPS energies this approach leads to results which are not unreasonable: what is usually described as a completely soft nonperturbative process can also be described in terms of gluons and quarks. The key element is the use of the saturation scale.

hep-ph↗

arXiv1999

Lower limits for E_T and N_ch from pQCD & hydrodynamics at the central rapidity unit in central Au-Au collisions at RHIC

Final state average transverse energy and charged particle multiplicity at the central rapidity unit of central Au-Au collisions at RHIC are studied within a framework of lowest order perturbative QCD and Bjorken's hydrodynamical picture. In particular, effects of initial minijet production and the $pdV$ work during the subsequent evolution of the QGP are investigated. Nuclear shadowing effects are included in a consistent manner, and the dependence of the results on the minijet transverse momentum cut-off parameter $p_0$ is shown.

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