Non-linear effects in hadronic interactions are treated by means of enhanced pomeron diagrams, assuming that pomeron-pomeron coupling is dominated by soft partonic processes. It is shown that the approach allows to resolve a seeming contradiction between realistic parton momentum distributions, measured in deep inelastic scattering experiments, and the energy behavior of total proton-proton cross section. Also a general consistency with both ``soft'' and ``hard'' diffraction data is demonstrated. An important feature of the proposed scheme is that the contribution of semi-hard processes to the interaction eikonal contains a significant non-factorizable part. On the other hand, the approach preserves the QCD factorization picture for inclusive high p_t jet production.
In hadronic collisions, the mini-jet cross section is formally divergent in the limit pT -> 0. We argue that this divergence is tamed by some effective colour correlation length scale of the hadron. A toy model of the hadronic structure is introduced, that allows an estimate of the screening effects, and especially their energy dependence.
We present our results on meson and nucleon screening masses in finite temperature two flavour QCD using smeared staggered valence quarks and staggered thin-link sea quarks with different lattice spacings and quark masses. We investigate optimization of smearing by observing its effects on the infrared (IR) and ultraviolet (UV) components of gluon and quark fields. The application of smearing to screening at finite temperature also provides a transparent window into the mechanism of the interplay of smearing and chiral symmetry. The improved hadronic operators show that above the finite temper…
We recently proposed a new approach to high energy nuclear scattering, which treats hadronic collisions in a sophisticated way. Demanding theoretical consistency as a minimal requirement for a realistic model, we provide a solution for the energy conservation, screening problems and identical elementary interactions, the so-called "Parton-Based Gribov-Regge Theory" including enhanced diagrams. We can now present some of our results for SPS and RHIC energies.
The Bloch-Nordsieck model for the parton distribution of hadrons in impact parameter space, constructed using soft gluon summation, is investigated in detail. Its dependence upon the infrared structure of the strong coupling constant $α_s$ is discussed, both for finite as well as singular, but integrable, $α_s$. The formalism is applied to the prediction of total proton-proton and proton-antiproton cross-sections, where screening, due to soft gluon emission from the initial valence quarks, becomes evident.
One year ago, we presented a new approach to treat hadronic interactions for the initial stage of nuclear collisions. It is an effective theory based on the Gribov-Regge formalism, where the internal structure of the Pomerons at high energies is governed by perturbative parton evolution, therefore the name "Parton-Based Gribov-Regge Theory". The main improvement compared to models used so-far is the appropriate treatment of the energy sharing between the different elementary interactions in case of multiple scattering. It is clear that the above formalism is not yet complete. At high energies …
Using an unquenched lattice potential to calculate the spectrum of the bottomonium system, we demonstrate numerically that the effect of pair creation is to produce termination of hadronic Regge trajectories, in contrast to the Veneziano model and the vast majority of phenomenological generalizations. Termination of Regge trajectories may have significant experimental consequences.
The influence of non-linear interaction effects on the characteristics of hadronic collisions and on the development of extensive air showers (EAS) is investigated. Hadronic interactions are treated phenomenologically in the framework of Gribov's Reggeon approach with non-linear corrections being described by enhanced (Pomeron-Pomeron interaction) diagrams. A re-summation algorithm for higher order enhanced graphs is proposed. The approach is applied to develop a new hadronic interaction model QGSJET-II, treating non-linear effects explicitely in individual hadronic and nuclear collisions. The…
The effects of color screening on the hadronization of a parton plasma into a hadron gas are examined at the energies of the relativistic heavy ion collider. It is found to have the tendency to prevent hadronization and therefore delaying the conversion of the partons into a hadron gas. Because of the continual expansion, the resulting hadron gas number densities are lower when screening is included. This should reduce the hadronic noise to genuine signals of the quark-gluon plasma. In this sense, color screening is favorable and should be included in numerical models. In any case, we advocate…
In this talk, multiquarks are studied microscopically in a standard quark model. In pure ground-state pentaquarks the short-range interaction is computed and it is shown to be repulsive, a narrow pentaquark cannot be in the groundstate. As a possible excitation, an additional quark-antiquark pair is then considered, and this is suggested to produce linear molecular system, with a narrow decay width. This excitation may be energetically favourable to the p-wave excitation suggested by the other pentaquark models. Here, the quarks assemble in three hadronic clusters, and the central hadron provi…
A feasible mechanism of unitarization of amplitudes of deep inelastic scattering at small values of Bjorken $x$ is the gluon fusion. However, its efficiency depends crucially on the vacuum color screening effect which accompanies the multiplication and the diffusion of BFKL gluons from small to large distances. From the fits to lattice data on field strength correlators the propagation length of perturbative gluons is $R_c\simeq 0.2-0.3$ fermi. The probability to find a perturbative gluon with short propagation length at large distances is suppressed exponentially. It changes the pattern of (d…
In this note we address the issue of measurability of the hadronic cross-sections at a future photon collider as well as for the two-photon processes at a future high energy linear $e^+e^-$ collider. We extend, to higher energy, our previous estimates of the accuracy with which the \gamgam\ cross-section needs to be measured, in order to distinguish between different theoretical models of energy dependence of the total cross-sections. We show that the necessary precision to discriminate among these models is indeed possible at future linear colliders in the Photon Collider option. Further we n…
Modelling multiple partonic interactions in hadronic events is vital for understanding minimum-bias physics, as well as the underlying event of hard processes. A brief overview of the current Pythia 8 multiple interactions (MI) model is given, before looking at two additional effects which can be included in the MI framework. With rescattering, a previously scattered parton is allowed to take part in another subsequent scattering, while with enhanced screening, the effects of varying initial-state fluctuations are modelled.
Using non-perturbative lattice method we studied hadronic screening correlators above and immediately below the deconfinement transition temperature, Tc, in the quenched approximation with lattice spacing of 1/(8T) using clover improved Wilson fermions. Simulations were performed at temperatures T /Tc = 0, 0.95 and 1.5. Mesonic screening correlators show no statistically significant thermal effects below Tc, and clear evidence for weakly interacting quarks above Tc . Baryon screening correlators yield similar physics above Tc, but show precursor effects for chiral symmetry restoration below Tc…
In a simplified model we study how close can the result of a fast, non-equilibrium hadronization of quark matter in an expanding fireball come to hadronic composition in equilibrium. We present a chemical approach to the simple A+B --> C quark fusion, showing ideal equilibrium constrained by conservation laws, the fugacity parametrization, as well as linear and non-linear quark coalescence models as different approximations to this chemistry. It is shown that color confinement requires a quark density dependent hadronization cross section.
The recently suggested interpretation of the universal hadronic freeze-out temperature T_f ~ 170 Mev - found for all high energy scattering processes that produce hadrons: e+ e-, p p, p anti-p, pi p, etc. and N N' (heavy-ion collisions) - as a Unruh temperature triggers here the search for the gravitational black-hole that in its near-horizon approximation better simulates this hadronic phenomenon. To identify such a black-hole we begin our gravity-gauge theory phenomenologies matching by asking the question: which black-hole behind that Rindler horizon could reproduce the experimental behavio…
In this note we address the issue of theoretical estimates of the hadronic cross-sections for \gamgam processes. We compare the predictions of the minijet model with data as well as other models, highlighting the band of uncertainties in the theoretical predictions as well as those in the final values of the $σ(\gamgam \go {\rm hadrons})$ extracted from the data. We find that the rise of $σ_{γγ}^{\rm tot}$ with energy shown in the latest \gamgam data is in tune with the faster rise expected in the Eikonal Minijet Models (EMM). We present an estimate of the accuracy with which this cross-sectio…
The study aims to investigate the observability of pseudoscalar Higgs boson $A$ and neutral heavy CP even Higgs boson $H$, at different benchmark points, in the framework of type-I 2HDM. The study is done for $e^{-}e^{+}$ collisions at $\sqrt{s}$ = 1000 GeV centre of mass energy (c.o.m.) a possible scenario in future lepton collider. The associated production of $A$ and $H$ in $e+ e-$ collisions are investigated in fully hadronic final state in two different channels. The first one is $AH \to ZHH \to j\bar{j} b \bar{b}b\bar{b}$ while the other one is $AH \to b \bar{b}b\bar{b}$. The observabili…
We calculate target fragmentation in $p p \to n X$ and $γp \to n X $ reactions in the meson cloud picture of the nucleon. The $p p \to n X$ reaction is used to fix the $pnπ^+$ form factor for two different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small $x_{Bj}$ electroproduction of forward neutrons at HERA. In photoproduction we observe about the same amount of absorption as in the hadronic reaction. For deep inelastic events ($Q^2>10$ GeV$^2$) screening is …
We consider the impact of O(alpha^2) hadronic corrections to the energy spectrum of the decay electron in muon decay. We find that the correction can be described, within good approximation, by a linear function in the electron energy. Explicit expressions for the form factors needed in an approach based on dispersion integrals are given.
It is proposed that soft particle production in hadronic collisions is dominated by multiple gluon exchanges between partons from the colliding hadrons, followed by radiation of hadronic clusters from the coloured partons distributed uniformly in rapidity. This explains naturally two dominant features of the data: (a) The linear increase of rapidity spectra in the regions of limiting fragmentation and, (b) the proportionality between the increasing width of the limiting fragmentation region and the height of the central plateau.
I present an overview of the ridge phenomenon in proton-proton and proton-lead collisions. This novel collimation between rapidity separated hadron pairs is a consequence of non-linear gluon dynamics within the small-x wave-function of the colliding hadrons.
We calculate target fragmentation in $p p \to n X$ and $γp \to n X $ reactions in the meson cloud picture of the nucleon. The $p p \to n X$ reaction is used to fix the $pnπ^+$ form factor for three different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small $x_{Bj}$ electroproduction of forward neutrons at HERA. Here the $q \bar q$ dipoles in the photon can rescatter on the residual neutron. In photoproduction we observe slightly less absorption than in the had…
Since a number of years the QGSJET model has been successfully used by different groups in the field of high energy cosmic rays. Current work is devoted to the first general update of the model. The key improvement is connected to an account for non-linear interaction effects which are of crucial importance for reliable model extrapolation into ultra-high energy domain. The proposed formalism allows to obtain a consistent description of hadron-hadron cross sections and hadron structure functions and to treat non-linear effects explicitely in individual hadronic and nuclear collisions. Other am…
We consider the O(alpha^2) hadronic corrections to the energy spectrum of the decay electron in muon decay. We find that the correction can be described, within good approximation, by a linear function in the electron energy. Explicit expressions for the form factors needed in an approach based on dispersion integrals are given.
High energy hadronic and nuclear interactions are described within Gribov's Reggeon scheme. An approach to re-summation of enhanced Pomeron graphs is proposed. The latter is applied to develop a new Monte Carlo model which treats non-linear interaction effects explicitely in individual hadronic collisions. On the other hand, we discuss a possible generalization of the scheme, which allows to account also for pQCD effects. In particular, this offers a possibility to fix model parameters on the basis of data on hadron-hadron cross sections, hadronic multi-particle production, and on total and di…
We study basic properties of scalar hadronic resonances within the so-called extended Linear Sigma Model (eLSM), which is an effective model of QCD based on chiral symmetry and dilatation invariance. In particular, we focus on the mass and decay width of the scalar isovector state $a_{0}(1450)$ and perform a numerical study of the propagator pole(s) on the unphysical Riemann sheets. In this work, this meson is understood as a seed state explicitly included in the eLSM. Our results show that the inclusion of hadronic loops does not modify much the previously obtained tree-level results. Moreove…
At high temperatures or densities, hadronic matter shows different forms of critical behaviour: colour deconfinement, chiral symmetry restoration, and diquark condensation. I first discuss the conceptual basis of these phenomena and then consider the description of colour deconfinement in terms of symmetry breaking, through colour screening and as percolation transition.
A specific value for the cosmological constant, Λ, can account for late-time cosmic acceleration. However, motivated by the so-called cosmological constant problem(s), several alternative mechanisms have been explored. To date, a host of well-studied dynamical dark energy and modified gravity models exists. Going beyond ΛCDM often comes with additional degrees of freedom (dofs). For these to pass existing observational tests, an efficient screening mechanism must be in place. The linear and quasi-linear regimes of structure formation are ideal probes of such dofs and can capture the onset of s…
We calculate the particle ratios for a strongly interacting hadronic matter matter using non-linear Walecka model (NLWM) in relativistic mean-field approximation. A comparison with Hadron Resonance Gas Model is made.
Within the Hadron-String Dynamics (HSD) transport approach we study the suppression pattern of charmonia at RHIC with respect to centrality and rapidity employing various model concepts such as variants of the 'comover absorption' model or the 'charmonium melting' scenario. We find that especially the ratio of the forward to mid-rapidity nuclear modification factors of J/Psi (R_AA (forward) / R_AA (mid)) cannot be explained by the interactions with 'formed' comoving mesons or by the 'color screening mechanism' alone. Only when incorporating interactions of the c or c-bar quark with a pre-hadro…
Scalar field theories that possess a Vainshtein mechanism are able to dynamically suppress the associated fifth forces in the presence of massive sources through derivative non-linearities. The resulting equations of motion for the scalar are highly non-linear and therefore very few analytic solutions are known. Here we present a brief investigation of the structure of Vainshtein screening in symmetrical configurations, focusing in particular on the spherical, cylindrical and planar solutions that are relevant for observations of the cosmic web. We consider Vainshtein screening in both the Gal…
New fifth forces have not yet been detected in the laboratory or in the solar system, hence it is typically difficult to introduce new light scalar fields that would mediate such forces. In recent years it has been shown that a number of non-linear scalar field theories allow for a dynamical mechanism, such as the Vainshtein and chameleon ones, that suppresses the strength of the scalar fifth force in experimental environments. This is known as screening, however it is unclear how common screening is within non-linear scalar field theories. k-essence models are commonly studied examples of non…
We investigate general frameworks for calculating transport coefficients for quasiparticle theories at finite temperature. Hadronic transport coefficients are then computed using the linear sigma model (LSM). The bulk viscosity over entropy density ($ζ/s$) is evaluated in the relaxation time approximation (RTA) and the specific shear viscosity ($η/s$) and static electrical conductivity ($σ_{el}/T$) are both obtained in the RTA and using a functional variational approach. Results are shown for different values of the scalar-isoscalar hadron vacuum mass with in-medium masses for the interacting …
Applying the HSD transport approach to charmonium dynamics within the 'hadronic comover model' and the 'QGP melting scenario', we show that the suppression pattern seen at RHIC cannot be explained by the interaction with baryons, comoving mesons and/or by color screening mechanism. The interaction with hadrons in the late stages of the collision (when the energy density falls below the critical) gives a sizable contribution to the suppression. On the other hand, it does not account for the observed additional charmonium dissociation and its dependence on rapidity. Together with the failure of …
The formation and suppression dynamics of J/Psi, Chi_c and Psi-Prime mesons is studied within the HSD transport approach for Au+Au reactions at the top RHIC energy of sqrt(S)=200 GeV. Two prominent models, which have been discussed for more than a decade, are incorporated, i.e. the 'hadronic comover absorption and reformation' model as well as the 'QGP threshold' scenario, and compared to available experimental data. Our studies demonstrate that both scenarios - compatible with experimental observation at SPS energies - fail severely at RHIC energies. This combined analysis - together with the…
The theoretical framework of the neutrino electron excitation at low energies including the screening effect in semiconductor detectors is developed for the first time, both in the Standard Model and in the presence of the neutrino magnetic moment. We explore the contribution of the screening effect of semiconductors to the neutrino electron excitation based on the linear response theory and calculate the corresponding numerical results. We show that excitation rates from the neutrino magnetic moment are dramatically enhanced {by} the screening effect and the sensitivity can be significantly i…
A future e+e- collider, such as the ILC or CLIC, would allow the Higgs sector to be probed with a precision significantly beyond that achievable at the High-Luminosity LHC. A central part of the Higgs programme at an e+e- collider is the model-independent determination of the absolute Higgs couplings to fermions and to gauge bosons. Here the measurement of the e+e-->HZ Higgsstrahlung cross section, using the recoil mass technique, sets the absolute scale for all Higgs coupling measurements. Previous studies have considered e+e- ->ZH with Z->l+l-, where l = electron or muon. In this paper it is…
Within the standard V - A theory of weak interactions, Quantum Electrodynamics (QED) and the linear sigma-model (LsM) of strong low-energy hadronic interactions we analyse gauge and infrared properties of hadronic structure of the neutron and proton in the neutron beta decay to leading order in the large nucleon mass expansion. We show that the complete set of Feynman diagrams describing radiative corrections of order O(α/π), induced by hadronic structure of the nucleon, to the rate of the neutron beta decay is gauge non-invariant and unrenormalisable. We show that a gauge non-invariant contri…
Many non-linear scalar field theories possess a screening mechanism that can suppress any associated fifth force in dense environments. As a result, these theories can evade local experimental tests of new forces. Chameleon-like screening, which occurs because of non-linearities in the scalar potential or the coupling to matter, is well understood around extended objects. However, many experimental tests of these theories involve objects with spatial extent much smaller than the scalar field's Compton wavelength, and which could therefore be considered point-like. In this work, we determine ho…
In 1998, J. M. Maldacena conjectured a precise duality in the low-energy (or decoupling) regime between a large N strongly-coupled SU(N) super-Yang-Mills theory defined in the four-dimensional Minkowski world-volume M^4 of a stack of N coincident D3-branes and the supergravity limit of a weakly-coupled type IIB closed superstring theory on AdS_5*S^5. This communication aims at introducing concepts and methods used to derive, in the gauge/string correspondence framework, the interaction potentials of mesons and baryons at zero and finite temperature. Especially, emphasize will be made on the li…
The formulation of the real and virtual photon production rate from strongly interacting matter is presented in the framework of finite temperature field theory. The changes in the hadronic spectral function induced by temperature are discussed within the ambit of the Walecka type model, gauged linear and non-linear sigma models, hidden local symmetry approach and QCD sum rule approach. Possibility of observing the direct thermal photon and lepton pair from quark gluon plasma has been contrasted with those from hot hadronic matter with and without medium effects for various mass variation scen…
Within the standard V - A theory of weak interactions, Quantum Electrodynamics (QED) and the linear sigma-model (LsM) of strong low-energy hadronic interactions we analyse infrared properties of hadronic structure of the neutron and proton in the neutron beta decays to leading order in the large nucleon mass expansion. We confirm validity and high confidence level of contributions of hadronic structure of the nucleon to the radiative corrections, calculated by Sirlin (Phys. Rev. 164, 1767 (1967)) to leading order in the large nucleon mass expansion. At the level of order 10^{-5} relative to Si…
We analyze the screening and bulk energy of a classical and strongly interacting plasma of color charges, a model we recently introduced for the description of a quark-gluon plasma at T=(1-3)Tc. The partition function is organized around the Debye-Huckel limit. The linear Debye-Huckel limit is corrected by a virial expansion. For the pressure, the expansion is badly convergent even in the dilute limit. The non-linear Debye-Huckel theory is studied numerically as an alternative for moderately strong plasmas. We use Debye theory of solid to extend the analysis to the crystal phase at very strong…
We consider how the occurrence of first-order phase transitions in non-constant pressure differs from those at constant pressure. The former has shown the non-linear phase structure of mixed matter, which implies a particle number dependence of the binding energies of the two species. If the mixed matter is mixed hadron-quark phase, nucleon outgoing from hadronic phase and ingoing to quark phase probably reduces the system to a non-equilibrium state, in other words, there exists the imbalance of the two phases when deconfinement takes place. This novel non-equilibrium process is very analogous…
We discuss the effect of dynamical charged particles in U(1)^{N-1} Abelian effective theories of QCD. Screening and confinement at zero temperature are explained qualitatively. The effect of dynamically charged particle is expressed in terms of an effective action of integer electric currents. When a screening is expected, the static potential shows a flattening in the long-range region and a linear behavior in the intermediate region. We show why the screening is better observed in the Polyakov-loop correlators than in the Wilson loops. The breaking of the adjoint string is explained without …
In order to characterize the higher order moments of the particle multiplicity, we implement the linear-sigma model with Polyakov-loop correction. We first studied the critical phenomena and estimated some thermodynamic quantities. Then, we compared all these results with the first--principle lattice QCD calculations. Then, the extensive study of non-normalized four moments is followed by investigating their thermal and density dependence. We repeat this for moments normalized to temperature and chemical potential. The fluctuations of the second order moment is used to estimate the chiral phas…
Within the standard V - A theory of weak interactions, Quantum Electrodynamics (QED) and the linear sigma-model (LsM) of strong low-energy hadronic interactions we analyse gauge properties of hadronic structure of the neutron and proton in the neutron radiative beta-decay. We show that the Feynman diagrams, describing contributions of hadronic structure to the amplitude of the neutron radiative beta-decay in the tree-approximation for strong low-energy interactions in the LsM, are gauge invariant. In turn, the complete set of Feynman diagrams, describing the contributions of hadron-photon inte…
We demonstrate that the instabilities in linear cosmological perturbations in bimetric theory are the manifestation of the non-linear Vainshtein mechanism on an FRW background. The spin-2 mass serves as the cosmological Vainshtein scale in this case. This allows us to quantitatively address early universe cosmology. In particular, in a global analysis, we study data from the cosmic microwave background radiation and local measurements of the Hubble flow. We show that bimetric cosmology resolves the discrepancy in the local and early-time measurements of the Hubble scale via an effective phanto…
