The Standard Model of elementary particles successfully describes the high energy experiments. The great leap in the recent years was the discovery of the Higgs boson at the Large Hadron Collider (LHC) at CERN. The mass of the Higgs is 125 GeV, which implies that the Standard Model could be valid up to the Planck scale, where gravity must be taken into account . Observations in astrophysics and cosmology suggest new fields or particles, as nearly seventy percent of the Universe is dark energy and approximately one quarter is non-baryonic dark matter. Particle theorists proposed a large number of dark matter models. The hypothetical new particles generally couple to the newly discovered Higgs boson, this way the Higgs opens a portal to new physics. The study of simplified models coupled to the Standard Model in field theory and phenomenology is an important and active research area. These help us to learn more about the viability, scales and parameters of complex models. The new phenomena and particles can be tested at the 13 TeV run starting in 2015 at the LHC.Selected papers: G. Cynolter, E. Lendvai, G. Pocsik: Note on unitarity constraints in a model for a singlet scalar dark matter candidate Acta Phys.Polon. B36 (2005) 827-832 G. Cynolter, J . Kovács, E. Lendvai: Diphoton excess and VV-scattering Mod.Phys.Lett. A31 (2016) no.22, 1650133
Effective field theories are important in particle physics, built on the relevant degrees of freedom. Even the Standard Model of Electroweak Interactions is generally accepted to be an effective theory. Effective field theories have a well defined range of validity, most easily taken into account by a cutoff. The naive momentum cutoff however breaks the space-time and gauge symmetries in the theory. On the other hand in the presence of gravity or supersymmetry calculations in four dimensions are preferred, as in these cases the most widely used dimensional regularization faces problems. We worked out a regularization method proposed in four dimensions, which defines a cutoff respecting the symmetries of the models. As applications of the improved symmetry preserving cutoff we studied the effects of one-loop corrections in effective and non-renormalizable models.Selected papers: G. Cynolter, E. Lendvai: Symmetry Preserving Regularization with A Cutoff Central Eur.J.Phys. 9 (2011) 1237-1247 G. Cynolter, E. Lendvai: Electroweak Precision Constraints on Vector-like Fermions Eur.Phys.J. C58 (2008) 463-469 G. Cynolter, E. Lendvai: Corrections to gauge theories in effective quantum gravity with a cutoff Mod.Phys.Lett. A29 (2014) 1450024
Laws of particle physics break down under the condition of strong gravitational fields, like for example in the physics of black holes The reason is that at very small scales the classical geometry of Einstein's general relativity is not welldefined, and looses validity. For a consistent theory of quantum gravity we need to drop a fundamental physical assumption: in string theory particles at tiny scales are not anymore point like, rather they are described by onedimensional objects, called strings. String theory today is organized by the AdS/CFT principle, which states that string theory in a given region of space can be described by a dual field theory, existing on the boundary of thiis region. So, string theory and field theories cannot be regarded as different constructions, and for field theories in the strong coupling region the gravity description may be more appropriate. Our research focuses on one hand on the mathematical structure of string theory, and on the other hand we develop string theory methods for describing strongly coupled physical systems, related those in condensed matter theory.Selected papers: S. Cremonini and A. Sinkovics: Spatially Modulated Instabilities of Geometries with Hyperscaling Violation, JHEP 1401, 099 (2014), [arXiv:1212.4172 [hepth], arXiv:1212.4172]. Z. Kökényesi, A. Sinkovics and R. J. Szabo: Refined ChernSimons theory and (q, t)deformed YangMills theory: Semiclassical expansion and planar limit, JHEP 1310, 067 (2013), [arXiv:1306.1707 [hepth]].