Welcome to the Journal of Holography Applications in Physics (JHAP). It covers all areas related to the holographic principle in physics, a new place of communication for research. Holographic principle prepares the powerful tools to study several phenomena in various branches of physics. However, there is no specialized journal on these topics. The aim of JHAP is to collect all applications of holography for the theoretical and experimental communities. A variety of formats, including Regular Articles, Reviews, Scientific Notes, and Letters, are accepted. We would like to publish high-quality peer-reviewed papers, free of charge and open access for all readers. JHAP is fully sponsored by Damghan University. The reviewing and publishing process is completely free of charge.

     Holography is indeed one of the main consequences of the string theory, which relates two different theories, for example, the quantum theory of gravity to the gauge field theory. The holographic principle has two sides, the firsts are quantum theories without gravity which are indeed experimentally relevant theories, and the others are classical theories of gravity, so applications in both (field theory and topology) are important. Applications of holography can relate some physics branches to each other like elementary particle physics, condensed matter physics, nuclear physics, astrophysics, and cosmology.

     The most famous application of holography well-known as AdS/CFT conjecture which suggests a relation between a conformal field theory (CFT) in d-dimensional space and a supergravity theory in (d+1)-dimensional anti-de Sitter (AdS) space. It is indeed usage of topology to study strongly coupled systems like quantum chromodynamics (QCD) at finite temperature or condensed matter theory (CMT). The former includes the study of the quark-gluon plasma (QGP) in four-dimensional space-time by using the string theory in five-dimensional AdS space-time. It is an elementary particle physics application (sometimes called the AdS/QCD correspondence), which is tested in modern particle accelerators. The latter includes a field theory description of a system with the chemical potential at a finite temperature which is the holographic dual of a charged black hole. It is a condensed matter application that includes holographic models of superconductor and superfluid (sometimes called the AdS/CMT correspondence), thermal behaviors of Fermi liquids, holographic model of Weyl semimetal states, or study of field theory hydrodynamics using a gravitational solution. This aspect of holography some time called gauge/gravity duality. As mentioned above, having temperature on the gauge field theory side is corresponding to have a black hole on the gravity side. Therefore, the study of black hole dynamics is important for holographic studies. Black holes also are important from another holographic point of view. The event horizon area of the black hole is as the holographic dual of the black hole entropy, and the black hole surface gravity is as the holographic dual of the black hole temperature. So, it helps us to study the black hole thermodynamics. It is indeed like a hologram where the maximum information of bulk is proportional to its area.

     At low (intermediate) temperatures physics where the theory is in confinement state, the only configuration is a connected eight-brane, there is a second-order phase transition at finite chemical potential (vacuum) to a nuclear matter phase. Moreover, chiral dynamics of hadrons, like baryons at low energy physics which are typical of strongly coupled QCD (bound state of 3 quarks via strong coupling) can be investigated using holography to calculate corresponding binding energy which also may test in experiments. Studying the nuclear force using string theory is one of the most important applications of holography. These are some applications of holography in nuclear physics which are another aspect of AdS/QCD.

     Application of the holographic principle to the dark energy problem in cosmology has been known as holographic dark energy. The study of de Sitter (dS) space-time and inflation is also important from dS/CFT as well as AdS/CFT correspondence point of view. Holographic descriptions of inflationary universes can relate the cosmological observables, like the primordial power spectrum, to the correlation functions of a quantum field theory (QFT).

     Neutron stars are interesting systems for the holographic application in astronomy and astrophysics. These systems include matter at low temperature while very high density (which yields to the existence of a deconfined quark phase), however, it is not so hot for application of perturbative QCD. Hence, AdS/CFT correspondence can help to study the neutron star equation of state. In that case, it has been suggested that degenerate composite operators of CFT are considered as holographic dual to degenerate stars in AdS space.

     The applications of holography in laser and photonics are also broad interesting, such as the image reconstruction of objects, the generation of novel laser beams, and new designs in photonic micro- and nano-structures, etc.

     All the above motivations say that holography applications in physics are an interesting and important field of research for more than two decades, in which hundreds of papers have been published. In this way, and considering the importance of the holography and its applications, we decided to publish the JHAP, which covers all areas related to holography.

Prof. S A Ketabi

Editor-in-Chief