Table of contents

Once upon a time, the world was simple: the proton contained three quarks, two ups and a down. How these give the proton its mass and its spin seemed obvious. Over the past 40 years the proton has become more complicated, and how even these most obvious of its properties is explained in a universe of quarks, antiquarks and gluons remains a challenge. That this should be so should come as no surprise. Quantum chromodynamics, the theory of the strong interaction, is seemingly simple, and its consequences are straightforward in the domain of hard scattering where perturbation theory applies. However, the beauty of the hadron world is its diversity. The existence of hadrons, their properties, and their binding into nuclei do not appear in the Lagrangian of QCD. They all emerge as a result of its strong coupling. Strong coupling QCD creates complex phenomena, much richer than known 40 years ago: a richness that ensures colour confinement and accounts for more than 95% of the mass of the visible Universe. How strong coupling QCD really works requires a synergy between experiment and theory. A very personal view of these fascinating developments in cold QCD is presented.

We present a comparative analysis of the impact of the non-perturbative intrinsic charm quark content of a proton on the differential cross section of a $\gamma + c$-jet in pp and $p\bar{p}$ collisions, for the kinematic regions that are sensitive to this contribution. We discuss the Q² evolution of intrinsic quark distributions at the next-to-leading order (NLO) and present a code which provides these distributions as a function of x and Q² for any arbitrary Fock state probability. For the $p\bar{p}$ collisions at the Tevatron, the results are compared with recent experimental data at $\sqrt{s}=1.96$ TeV and also predictions for pp collisions at $\sqrt{s}=8$ TeV and $\sqrt{s}=13$ TeV for the Large Hadron Collider.

We investigate the mass and residue of Σ, Λ and Ξ hyperons at finite temperature in the framework of thermal QCD sum rules. In our calculation, we take into account the additional operators coming up at finite temperature. We find the temperature-dependent continuum threshold for each hyperon using the obtained sum rules for their mass and residue. The numerical results demonstrate that the mass and residue of the particles under consideration remain stable up to a certain temperature, after which they decrease by increasing the temperature.

Many data in the high energy physics are, in fact, sample means. It is shown that when this exact meaning of the data is taken into account and the most weakly bound states are removed from the hadron resonance gas, the acceptable fit to the whole spectra of pions, kaons and protons measured at midrapidity in central Pb–Pb collisions at $\sqrt{{s}_{{NN}}}=2.76$ TeV (2012 Phys. Rev. Lett. 109 252301) is obtained. The invariant distributions are predicted with the help of the single-freeze-out model in the chemical equilibrium framework. Low p_T pions and protons are reproduced simultaneously as well as the  $p/\pi$ ratio. Additionally, correct predictions extend over lower parts of large p_T data. Some more general, possible implications of this approach are pointed out.

Having in mind its future extension for theoretical investigations related to charmed nuclei, we develop a relativistic formalism for the nonmesonic weak decay (NMWD) of single-Λ hypernuclei in the framework of the independent-particle shell model and with the dynamics represented by the $(\pi ,K)$ one-meson-exchange model. Numerical results for the one-nucleon-induced transition rates of ${}_{{\rm{\Lambda }}}^{12}{\rm{C}}$ are presented and compared with those obtained in the analogous nonrelativistic calculation. There is satisfactory agreement between the two approaches, and the only noteworthy difference is that the ratio ${{\rm{\Gamma }}}_{n}/{{\rm{\Gamma }}}_{p}$ is appreciably higher and closer to the experimental value in the relativistic calculation. The ability of describing existing data, including the most recent ones, on NMWD of Λ-hypernuclei, warrants application of the formalism to evaluate similar decay processes in charmed nuclei.

The reaction of ⁷Li+¹²⁰Sn has been measured at bombarding energies of 21, 24 and 27 MeV. The ${2}^{+}\to {0}^{+}\;\gamma$-ray transition in ¹²⁰Sn was observed and the angular distribution for the 2⁺ excited state was obtained. Coupled channels and coupled-reaction channels calculations, including the dynamical polarization potential due to the projectile break-up, obtained from continuum discretized coupled channel calculations, were performed. The comparison between the existing experimental elastic angular distribution with the coupled-reaction channels calculations indicates that the 1n stripping transfer is the most intense channel to be coupled and the 2n stripping reaction occurs sequentially rather than directly, however, further data must be analyzed to confirm this indication. The experimental elastic and inelastic scattering data were well described by the calculations, but some discrepancies in these channels may indicate the need for corrections to the nuclear potential and/or the necessity to incorporate further channels.

The scattering of electrons off nuclei is one of the best methods of probing nuclear structure. In this paper we focus on electron scattering off nuclei with spin and isospin zero within the Skyrme model. We consider two distinct methods and simplify our calculations by use of the Born approximation. The first method is to calculate the form factor of the spherically averaged Skyrmion charge density; the second uses the Patterson function to calculate the scattering intensity off randomly oriented Skyrmions, and spherically averages at the end. We compare our findings with experimental scattering data. We also find approximate analytical formulae for the first zero and first stationary point of a form factor.

Utilizing the in-medium Lorentz decomposition of operators generating QCD condensates we derive general constraints among the latter ones by the requirement of a smooth transition from medium to vacuum. In this way we relate the vacuum limits of heretofore unrelated condensates and provide consistency checks for the vacuum saturation hypothesis and the heavy quark mass expansion. The results are general and depend only on the rank and symmetry of the Lorentz tensors to be decomposed. The derived prescription enables to uniquely and directly identify operator product expansion contributions which are algebraically specific for in-medium situations and in particular useful for operators with a higher rank, i.e. larger than three. Four-quark condensates in mass dimension six are exemplified.

We present a new perturbative expansion for pionless effective field theory with Coulomb interactions in which at leading order (LO) the spin-singlet nucleon–nucleon channels are taken in the unitarity limit. Presenting results up to next-to-leading order for the Phillips line and the neutron–deuteron doublet-channel phase shift, we find that a perturbative expansion in the inverse ${}^{1}{S}_{0}$ scattering lengths converges rapidly. Using a new systematic treatment of the proton–proton sector that isolates the divergence due to one-photon exchange, we renormalize the corresponding contribution to the ${}^{3}{\rm{H}}$ –${}^{3}\mathrm{He}$ binding energy splitting and demonstrate that the Coulomb force in pionless EFT is a completely perturbative effect in the trinucleon bound-state regime. In our new expansion, the LO is exactly isospin-symmetric. At next-to-leading order, we include isospin breaking via the Coulomb force and two-body scattering lengths, and find for the energy splitting ${({E}_{B}{(}^{3}\mathrm{He})-{E}_{B}{(}^{3}{\rm{H}}))}^{\mathrm{NLO}}\quad =(-0.86\pm 0.17)\quad \mathrm{MeV}$.

Over the past few years, there has been a hint of the γ-ray excess observed by the Fermi-LAT satellite-borne telescope from the regions surrounding the galactic centre (GC) at an energy range of ∼1–3 GeV. The nature of this excess γ-ray spectrum is found to be consistent with the γ-ray emission expected from dark matter (DM) annihilation at the GC while disfavouring other known astrophysical sources as the possible origin of this phenomena. It is also reported that the spectrum and morphology of this excess γ-rays can well be explained by the DM particles having mass in the range $30\mbox{--}40\;{\rm{GeV}}$ annihilating significantly into $b\bar{b}$ final state with an annihilation cross section $\sigma v\sim (1.4$–$2.0)\times {10}^{-26}$ cm${}^{3}\;{{\rm{s}}}^{-1}$ at the GC. In this work, we propose a two-component DM model where two different types of DM particles, namely a complex scalar and a Dirac fermion are considered. The stability of both the dark sector particles are maintained by virtue of an additional local ${\rm{U}}{(1)}_{X}$ gauge symmetry. We find that our proposed scenario can provide a viable explanation for this anomalous excess γ-rays besides satisfying all the existing relevant theoretical as well as experimental and observational bounds from LHC, PLANCK and LUX collaborations. The allowed range of 'effective annihilation cross section' of lighter DM particle for the $b\bar{b}$ annihilation channel thus obtained is finally compared with the limits reported by the Fermi-LAT and DES collaborations using data from various dwarf spheroidal galaxies.