Dear Colleagues,

The birth of the universe out of the M-theory landscape remains an important question in modern cosmology. Questions such as “Why are the only three large spatial dimensions?”, “What drives inflation?”, and “Is there observable evidence of the birth of the universe out of the M-theory landscape?” are subjects of active debate. We invite colleagues to submit papers on the following topics:

Trans-Plankian inflation
Models of inflation
Constraints on Inflation effective potentials
Brane-world inflation
Constraints on Inflation initial conditions
Primordial gravitational waves
Cosmic dark flow and large-scale structure
Origin of the cold spot in the CMB
Anomalies in the CMB from inflation and the M-theory landscape
Supersymmetric Inflation
Primordial nucleosynthesis constraints on the birth of the universe
Constraints on time-varying fundamental constants
Constraints on anisotropic cosmological models
Why are there three large dimensions

Prof. Dr. Grant J. Mathews
Prof. Dr. Laura Mersini Houghton
Guest Editors

Dear Colleagues,

It is a pleasure to announce the Special Issue “Quantum Field Theory XXI”. Since its first applications in the XX century, and the crowning with the formulation of the Standard Model of electroweak and strong interactions, quantum field theory has evolved, both in meaning and intention. Its perturbative and nonperturbative incarnations have been playing an undisputed role in modern theoretical physics, not only in the refinement of the Standard Model and of its supersymmetric extensions, but also in the quest for a quantum theory of gravitation, carried on in the programs of string theory, supergravity, and many other quantum gravities (nonlocal quantum gravity, asymptotic safety, group field theory, and so on), and in our understanding of astrophysical and cosmological processes, ranging from the Big Bang to stellar evolution, and from the cosmological constant to gravitational waves.

This Special Issue aims to recapitulate part of these achievements and offer a perspective on near- and far-future applications of quantum field theory in the present century. Review and perspective papers are especially welcome.
Gianluca Calcagni
Guest Editor

Dear Colleagues,

Quantum Chromodynamics (QCD) encodes a large richness of physical phenomena, and is intensively studied theoretically and experimentally. However, in spite of its success, some of its aspects are not yet fully understood; there remain open questions that demand answers. Most of these questions have important implications in cosmology and astroparticle physics.

The QCD Lagrangian contains ingredients that can clarify key questions concerning cosmology. The term, which breaks conformal symmetry, even in the massless case, is related to the axion field and its search concerns the nature of dark matter and also could contribute to the cosmological constant. Other possibilities of dark matter have been speculated, such as the existence of exotic hadrons made of color-octet complexes. The mentioned term, which is not CP invariant, plays an important role in the equation of the state of the deconfinement transition from hadronic matter to quark gluon matter, such as what happened in the first moments of the Universe after the Big Bang. This term is proportional to the trace anomaly, which measures the departure from a free quark-gluon gas of the obtained strongly-coupled quark gluon matter, and is also related to vacuum structure.

The experiments of the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) have created strongly-coupled quark gluon matter in nucleus–nucleus collisions. Most of the observed collective effects have also been seen in pp collisions. In this case, it is not clear how hydrodynamic models can be applied. There is not a unified picture of the transverse momentum distribution of pp data, as well as its azimuthal distribution. The interplay between soft and hard collisions can show interesting relationships between parton entanglement and thermalization. On the other hand, the forward LHC detectors provide important information on elastic and diffractive scattering, which play important roles in determining the hadronic cascade produced in ultrarelativistic cosmic rays. Usual hadronic models, previously-matched to LHC data, are not able to describe some of the cosmic ray data at higher energies, such as the excess of muons and the energy dependence of the distribution of the length of maximum depth. Phenomena like gluon saturation, color reconnection, string interactions, percolation, and string junction working at LHC energies could have implications in the hadronic cascade.

The QCD conformal breaking term, the axion field and the relation to dark matter and the cosmological constant, the strong CP problem, the dependence on the temperature of the trace anomaly, the equation of state close to the deconfinement phase transition, the collective effects produced in colliding small systems and its thermalization, the transverse momentum distributions, including azimuthal distributions and the interplay between soft and hard interactions, the elastic and diffractive scatterings and in general forward physics at LHC and ultrahigh cosmic ray energies, models of hadronic cascade are the subject of special interest at an interplay of QCD with two related fields: Cosmology and Astroparticle Physics.

Prof. Dr. Carlos Pajares
Guest Editor

Dear Colleagues,

F(R) gravity plays a prominent role in the description of gravitational phenomena at large and astrophysical scales. Among the various modified gravity proposals, the F(R) gravity framework is the conceptually simplest generalization of Einstein’s gravity, and has attracted the interest of many cosmologists. In this special issue, the focus will be on applications of F(R) gravity at large and astrophysical scales. We aim to highlight a plethora of theoretical proposals that find explanation in the context of F(R) gravity, both in cosmology and in astrophysics. In view of the current observational data and also due to the upcoming observations, this issue aims to gather all the up to date facts with regard to F(R) gravity applications. All the above problems maybe also be considered in frames of other modified gravities, like modified Gauss-Bonnet gravity, string-inspired theory, teleparallel gravity, Born-Infeld type gravity or non-minimal modified gravity.

Dr. Vasilis K. Oikonomou
Prof. Dr. Sergei D. Odintsov
Guest Editors