Qcd Research Papers - Academia.edu (original) (raw)

We study the nucleon and diquarks in a non-local Nambu-Jona-Lasinio model. For certain parameters the model exhibits quark confinement, in the form of a propagator without real poles. After truncation of the two-body channels to the... more

We study the nucleon and diquarks in a non-local Nambu-Jona-Lasinio model. For certain parameters the model exhibits quark confinement, in the form of a propagator without real poles. After truncation of the two-body channels to the scalar and axial-vector diquarks, a relativistic Faddeev equation for nucleon bound states is solved in the covariant diquark-quark picture. The dependence of the nucleon mass on diquark masses is studied in detail. We find parameters that lead to a simultaneous reasonable description of pions and nucleons. Both the diquarks contribute attractively to the nucleon mass. Axial-vector diquark correlations are seen to be important, especially in the confining phase of the model. We study the possible implications of quark confinement for the description of the diquarks and the nucleon. In particular, we find that it leads to a more compact nucleon.

Memoria de tesis doctoral dirigida por Ángel Gómez NIcola.
Departamento de Física Teórica II,
Universidad Complutense de Madrid.

We discuss the stringy properties of high-energy QCD using its hidden integrability in the Regge limit and on the light-cone. It is shown that multi-colour QCD in the Regge limit belongs to the same universality class as superconformal... more

We discuss the stringy properties of high-energy QCD using its hidden integrability in the Regge limit and on the light-cone. It is shown that multi-colour QCD in the Regge limit belongs to the same universality class as superconformal Script N = 2 SUSY YM with Nf = 2Nc at the strong coupling orbifold point. The analogy with integrable structure governing

We discuss recent advances on QCD chiral symmetry restoration at finite temperature , within the theoretical framework of Effective Theories. U(3) Ward Identities are derived between pseudoscalar susceptibilities and quark condensates,... more

We discuss recent advances on QCD chiral symmetry restoration at finite temperature , within the theoretical framework of Effective Theories. U(3) Ward Identities are derived between pseudoscalar susceptibilities and quark condensates, allowing to explain the behaviour of lattice meson screening masses. Unitarized interactions and the generated f 0 (500) thermal state are showed to play an essential role in the description of the transition through the scalar susceptibility.

In this work we estimate the heavy quark production in the interaction of ultra high energy cosmic rays in the atmosphere, considering that the primary cosmic ray is a proton or a photon. At these energies the saturation momentum... more

In this work we estimate the heavy quark production in the interaction of ultra high energy cosmic rays in the atmosphere, considering that the primary cosmic ray is a proton or a photon. At these energies the saturation momentum Q_{sat}^2 stays above the hard scale \mu_c^2=4m_c^2, implying charm production probing the saturation regime. In particular, we show that the ep HERA data presents a scaling on \tau_c = (Q^2+\mu_c^2)/Q_{sat}^2. We derive our results considering the dipole picture and the Color Glass Condensate formalism, which one shows to be able to describe the heavy quark production in photon-proton and proton-proton collisions. Nuclear effects are considered in computation of cross sections for scattering on air nuclei. Implications on the flux of prompt leptons at the earth are analyzed and a large suppression is predicted.

The Generalized Uncertainty Principle (GUP), which has been predicted by various theories of quantum gravity near the Planck scale is implemented on deriving the thermodynamics of ideal Quark-Gluon Plasma (QGP) consisting of two massless... more

The Generalized Uncertainty Principle (GUP), which has been predicted by various theories of quantum gravity near the Planck scale is implemented on deriving the thermodynamics of ideal Quark-Gluon Plasma (QGP) consisting of two massless quark flavors at the hadron-QGP phase equilibrium and at a vanishing chemical potential. The effective degrees of freedom and MIT bag pressure are utilized to distinguish between the hadronic and partonic phases. We find that GUP makes a non-negligible contribution to all thermodynamic quantities, especially at high temperatures. The asymptotic behavior of corresponding QGP thermodynamic quantities characterized by the Stephan-Boltzmann limit would be approached, when the GUP approach is taken into consideration.

In this paper it has been tried to propose a hypothesis for Universe life cycle from its birth to death along with a cyclic view into its rebirth referring to the concept of Cosmic Microwave Background Radiation, Spiral Structure of... more

In this paper it has been tried to propose a hypothesis for Universe life cycle from its birth to death along with a cyclic view into its rebirth referring to the concept of Cosmic Microwave Background Radiation, Spiral Structure of Galaxies and Spiral Structure of Elementary Particles. It has been tried to inherit the behaviour of Big Bang in consensus with the proposals of Steady State Cosmology within the vicinity of all modern ongoing researches. It also provides a unified approach for various force interactions of particles through the intrinsic behaviours of Spiral Structure of Elementary Particles. The inverse relation between mass of particle and rate of change of cross section of spiral arms gives us a distinct view of gravitational interactions. Also the orientation of the curl of spiral differentiate the electromagnetic interaction when has revolution and electroweak interaction when has rotational curl. Strong interaction can be described through the phase differences of particles with charge not in multiple of ½. This paper also describes the process for formation off composite particles and the atomic structure through various dynamics of interactions by spiral structured particles.

We discuss non-perturbative QCD contributions to jet observables, computing their dependence on the jet radius R, and on the colour and transverse momentum of the parton initiating the jet. We show, using analytic QCD models of power... more

We discuss non-perturbative QCD contributions to jet observables, computing their dependence on the jet radius R, and on the colour and transverse momentum of the parton initiating the jet. We show, using analytic QCD models of power corrections as well as Monte Carlo simulations, that hadronisation corrections grow at small values of R, behaving as 1/R, while underlying event contributions grow with the jet area as R^2. We highlight the connection between hadronisation corrections to jets and those for event shapes in e^+e^- and DIS; we note the limited dependence of our results on the choice of jet algorithm; finally, we propose several measurements in the context of which to test or implement our predictions. The results presented here reinforce the motivation for the use of a range of R values, as well as a plurality of infrared-safe jet algorithms, in precision jet studies at hadron colliders.

Two technical and two physics analyses are reported in this thesis, which were carried out using data recorded by CMS at √s = 8 TeV. The first technical contribution is related to the improvement of the performance of the CMS tracking... more

Two technical and two physics analyses are reported in this thesis, which were carried out using data recorded by CMS at √s = 8 TeV. The first technical contribution is related to the improvement of the performance of the CMS tracking detector, which provides measurements of trajectories of charged particles, and is relevant fornearly every physics analysis at CMS. A new method was studied for Lorentz-angle estimation and correction for the lost signal due to the short readout time between subsequent proton-bunch crossings. Such parameters are determined simultaneously with the tracker geometry, which allows to include correlations between different effects and to even absorb unknown or mismodelled ones. The obtained results show an improvement of hit-position resolution, which is more stable in time compared to standalone measurements. Possible ways of further improvement of the methodare also proposed.In the second technical contribution, a standalone software package was developed for the identification of the origin of jets initiated by bottom quarks (b jets)in Monte Carlo (MC) simulations. It allows to differentiate at generator level between b jets originating from decays of e.g. a top-quark, or a Higgs boson, or a Zboson, based on the actual particle relations stored in the simulated event. This functionality is crucial for the presented physics analyses, and it did not exist inCMS before. Its generic implementation provides equally high performance with allparton-shower generators that are used at CMS, and was chosen as a recommendedway of heavy-flavour-jet definition in future CMS analyses.As one of the primary results of this thesis, the cross sections of top-quark-pairproduction in association with at least one (ttb(b)) or at least two (ttbb) b jets with pT > 20 GeV were measured differentially as functions of transverse momentum (pT ) and absolute pseudorapidity (|η|) of the first or the second additional b jetrespectively. The ttbb cross section was also measured as a function of the angulardistance (∆Rbb ) and of the invariant mass (mbb ) of the two additional b jets. Thelatter provides substantial sensitivity to the ttH process, to which ttbb is an almostirreducible background, therefore the data is blinded in the ttH-enhanced invariantmass region. The dileptonic final state of the tt process is considered to minimisethe probability of possible jet misassignments. The measured ttb(b) (ttbb) crosssection is about 1.9 (1.3) times higher than predicted by MC simulations, which isin agreement with the previous inclusive ttbb cross-section measurement by CMS.The shapes of the measured cross sections are well modelled by MC predictions,except for the ∆Rbb spectrum, which shows a tendency towards smaller simulatedseparation between additional b jets than measured in the data.The measured ttb(b) and ttbb cross sections were used to estimate the sensitivityto the ttH(bb) process based on MC simulations, without systematic-uncertaintiestreatment. Several approaches of candidate jet-pair selection were studied, whichaim at the extraction of the ttH signal from the mbb distribution, which is a wellunderstood physical quantity. The highest signal-over-background ratio reached is 1/9, at which the ttH-signal significance is 0.18σ for the available 19.7 fb−1 of data.√A rough estimate of the sensitivity with future data recorded at s = 14 TeV showedthat about 130 fb−1 of data should be sufficient to see a mass peak from H → bbdecays with a significance of 2σ.

We compute the potential between a pair of nucleons in the D4-D8 holographic QCD. In the large 't Hooft coupling limit, lambdagg1\lambda \gg 1lambdagg1, the hadronic size of the baryon is small sim1/sqrtlambdaMKK\sim 1/\sqrt{\lambda}M_{KK}sim1/sqrtlambdaMKK, and their interaction with... more

We compute the potential between a pair of nucleons in the D4-D8 holographic QCD. In the large 't Hooft coupling limit, lambdagg1\lambda \gg 1lambdagg1, the hadronic size of the baryon is small sim1/sqrtlambdaMKK\sim 1/\sqrt{\lambda}M_{KK}sim1/sqrtlambdaMKK, and their interaction with mesons are well approximated by a set of dimension four and five operators. The nucleon-nucleon potential emerges from one-boson exchange picture involving massless pseudo-scalars and an infinite tower of spin one mesons. We find in particular that rho\rhorho meson exchanges are dominated by a dimension five derivative coupling of tensor type, whereas for omega\omegaomega mesons and axial mesons, such tensor couplings are completely absent. The potential is universally repulsive sim1/r2\sim 1/r^2sim1/r2 at short distance, and has the usual long-distance attractive behavior sim−1/r3\sim -1/r^3sim−1/r3 along a isosinglet and spin triplet channel. Both the large NcN_cNc form and the finite NcN_cNc form are given. In the former, a shallow classical minimum of depth sim0.1MKKNc/lambda\sim 0.1M_{KK}{N_c/\lambda}sim0.1MKKNc/lambda forms at around rMKKsimeq5.5rM_{KK}\simeq 5.5rMKKsimeq5.5.

Mass- and wave-function renormalization is calculated to order p4p^4p4 in heavy baryon chiral perturbation theory. Two different schemes used in the literature are considered. Several technical issues like field redefinitions,... more

Mass- and wave-function renormalization is calculated to order p4p^4p4 in heavy baryon chiral perturbation theory. Two different schemes used in the literature are considered. Several technical issues like field redefinitions, non-transformation of sources as well as subtleties related to the definition of the baryon propagator are discussed. The nucleon axial-vector coupling constant gAg_AgA is calculated to order p4p^4p4 as an illustrative example.

In this article we propose the calculation of the unconditional Wiener measure functional integral with a term of the fourth order in the exponent by an alternative method as in the conventional perturbative approach. In contrast to the... more

In this article we propose the calculation of the unconditional Wiener measure functional integral with a term of the fourth order in the exponent by an alternative method as in the conventional perturbative approach. In contrast to the conventional perturbation theory, we expand into power series the term linear in the integration variable in the exponent. In such a case we can profit from the representation of the integral in question by the parabolic cylinder functions. We show that in such a case the series expansions are uniformly convergent and we find recurrence relations for the Wiener functional integral in the NNN - dimensional approximation. In continuum limit we find that the generalized Gelfand - Yaglom differential equation with solution yields the desired functional integral (similarly as the standard Gelfand - Yaglom differential equation yields the functional integral for linear harmonic oscillator).

Starting from the observation that colour charge is only well defined on gauge invariant states, we construct perturbatively gauge invariant, dynamical dressings for individual quarks. Explicit calculations show that an infra-red finite... more

Starting from the observation that colour charge is only well defined on gauge invariant states, we construct perturbatively gauge invariant, dynamical dressings for individual quarks. Explicit calculations show that an infra-red finite mass-shell renormalisation of the gauge invariant, dressed propagator is possible and, further, that operator product effects, which generate a running mass, may be included in a gauge invariant way in the propagator. We explain how these fields may be combined to form hadrons and show how the interquark potential can now be directly calculated. The onset of confinement is identified with an obstruction to building a non-perturbative dressing. We propose several methods to extract the hadronic scale from the interquark potential. Various extensions are discussed.

Abstract This paper discusses and applies a basis for modeling elementary forces and particles. We show that models based on isotropic quantum harmonic oscillators describe aspects of the four traditional fundamental physics forces and... more

Abstract This paper discusses and applies a basis for modeling elementary forces and particles. We show that models based on isotropic quantum harmonic oscillators describe aspects of the four traditional fundamental physics forces and point to some known and possible elementary particles. We summarize results from models based on solutions to equations featuring isotropic pairs of isotropic quantum harmonic oscillators. Results include predictions for new elementary particles and possible descriptions of dark matter and dark energy.