arXiv subjects

Z. Kepuladze

Publications and source records attributed to Z. Kepuladze.

7 recordsLinked to original sources

arXiv2025

Unified Pati-Salam from Noncommutative Geometry: Overview and Phenomenological Remarks

The lack of clear new-physics signals at the LHC searches motivates models that can guide current and future collider searches. The spectral action principle within the noncommutative geometry (NCG) framework yields such models with distinctive phenomenology. This formalism derives the actions of the Standard Model, General Relativity, and beyond from the underlying algebra, putting them on a common geometric footing. Certain versions of Pati-Salam (PS) models with gauge coupling unification and limited scalar content can be derived from an appropriate noncommutative algebra. In this paper, I review these gauge-coupling-unified Pati-Salam models and discuss their phenomenological aspects, focusing on the $S_1$ scalar leptoquark.

hep-ph↗

arXiv2020

On the lightlike Lorentz violation

We consider the lightlike spontaneous Lorentz invariance violation (SLIV) appearing through the zero "length-fixing" constraint put on a gauge vector field, $A_{μ}A^{μ}=0$, and discuss its physical consequences in the framework of a conventional QED and beyond. Again, as in the timelike and spacelike SLIV cases, $A_{μ}A^{μ}=\pm M_{A}^{2}$ ($M_{A}$ is a scale of SLIV), while this constraint leads to an emergence of the Nambu-Goldstone modes collected in physical photon, the SLIV itself is still left unobservable unless gauge invariance in the theory is broken. At the same time, a crucial difference with the two former cases is that the asymmetrical vacuum corresponding to the lightlike Lorentz violation appears infinitely degenerated with all other vacua including the symmetrical one. We show that this degeneracy can be lifted out by introducing an extra gauge vector field being sterile with respect to an ordinary matter, though having some potential couplings with the basic $A_{μ}$ field. A slight mixing of them makes the underlying gauge invariance to be partially broken due to which physical Lorentz invariance occurs broken as well. This may cause a variety of the Lorentz violating processes some of which are briefly discussed.

hep-ph↗

arXiv2018

Emergent photons and gravitons

Now, it is already not a big surprise that due to the spontaneous Lorentz invariance violation (SLIV) there may emerge massless vector and tensor Goldstone modes identified particularly with photon and graviton. Point is, however, that this mechanism is usually considered separately for photon and graviton, though in reality they appear in fact together. In this connection, we recently develop the common emergent electrogravity model which would like to present here. This model incorporates the ordinary QED and tensor field gravity mimicking linearized general relativity. The SLIV is induced by length-fixing constraints put on the vector and tensor fields, $A_{μ}^{2}=\pm M_{A}^{2}$ and $H_{μν}^{2}=\pm M_{H}^{2}$ ($M_{A}$ and $M_{H}$ are the proposed symmetry breaking scales) which possess the much higher symmetry then the model Lagrangian itself. As a result, the twelve Goldstone modes are produced in total and they are collected into the vector and tensor field multiplets. While photon is always the true vector Goldstone boson, graviton contain pseudo-Goldstone modes as well. In terms of the appearing zero modes, theory becomes essentially nonlinear and contains many Lorentz and CPT violating interaction. However, as argued, they do not contribute in processes which might lead to the physical Lorentz violation. Nonetheless, how the emergent electrogravity theory could be observationally differed from conventional QED and GR theories is also briefly discussed.

physics.gen-ph↗

arXiv2018

Lorentzian Goldstone modes shared among photons and gravitons

It has long been known that photons and gravitons may appear as vector and tensor Goldstone modes caused \ by spontaneous Lorentz invariance violation (SLIV). Usually this approach is considered for photons and gravitons separately. We develop the emergent electrogravity theory consisting of the ordinary QED and the tensor field gravity model which mimics the linearized general relativity in Minkowski spacetime. In this theory, Lorentz symmetry appears incorporated into higher global symmetries of the length-fixing constraints put on the vector and tensor fields involved, $A_{μ}^{2}=\pm M_{A}^{2}$ and $H_{μν}^{2}=\pm M_{H}^{2}$ ($M_{A}$ and $M_{H}$ are the proposed symmetry breaking scales). We show that such a SLIV pattern being related to breaking of global symmetries underlying these constraints induces the massless Goldstone and pseudo-Goldstone modes shared among photon and graviton. While for a vector field case the symmetry of the constraint coincides with Lorentz symmetry $SO(1,3)$ of the electrogravity Lagrangian, the tensor field constraint itself possesses much higher global symmetry $SO(7,3)$, whose spontaneous violation provides a sufficient number of zero modes collected in a graviton. Accordingly, while photon may only contain true Goldstone modes, graviton appears at least partially composed from pseudo-Goldstone modes rather than from pure Goldstone ones. When expressed in terms of these modes, the theory looks essentially nonlinear and contains a variety of Lorentz and $CPT$ violating couplings. However, all SLIV effects turn out to be strictly cancelled in the lowest order processes that is considered in some detail. How this emergent electrogravity theory could be observationally differed from conventional QED and GR theories is also briefly discussed.

hep-th↗

arXiv2016

Gauge Symmetries Emerging from Extra Dimensions

We argue that extra dimensions with a properly chosen compactification scheme could be a natural source for emergent gauge symmetries. Actually, some proposed vector field potential terms or polynomial vector field constraints introduced in five-dimensional Abelian and non-Abelian gauge theory is shown to smoothly lead to spontaneous violation of an underlying 5D spacetime symmetry and generate pseudo-Goldstone vector modes as conventional 4D gauge boson candidates. As a special signature, there appear, apart from conventional gauge couplings, some properly suppressed direct multi-photon (multi-boson, in general) interactions in emergent QED and Yang-Mills theories whose observation could shed light on their high-dimensional nature. Moreover, in emergent Yang-Mills theories an internal symmetry G also occurs spontaneously broken to its diagonal subgroups once 5D Lorentz violation happens. This breaking origins from the extra vector field components playing a role of some adjoint scalar field multiplet in the 4D spacetime. So, one naturally has the Higgs effect without a specially introduced scalar field multiplet. Remarkably, when being applied to Grand Unified Theories this results in a fact that the emergent GUTs generically appear broken down to the Standard Model just at the 5D Lorentz violation scale M. PACS numbers: 11.15.-q, 11.30.Cp, 11.30.Pb, 11.10.Kk

hep-th↗

arXiv2012

Standard Model with Partial Gauge Invariance

We argue that an exact gauge invariance may disable some generic features of the Standard Model which could otherwise manifest themselves at high energies. One of them might be related to the spontaneous Lorentz invariance violation (SLIV) which could provide an alternative dynamical approach to QED and Yang-Mills theories with photon and non-Abelian gauge fields appearing as massless Nambu-Goldstone bosons. To see some key features of the new physics expected we propose partial rather than exact gauge invariance in an extended SM framework. This principle applied, in some minimal form, to the weak hypercharge gauge field B_{mu} and its interactions leads to SLIV with B field components appearing as the massless Nambu-Goldstone modes, and provides a number of distinctive Lorentz beaking effects. Being naturally suppressed at low energies they may become detectable in high energy physics and astrophysics. Some of the most interesting SLIV processes are considered in significant detail.

hep-ph↗

arXiv2008

Spontaneous Lorentz Violation via QED with Non-Exact Gauge Invariance

We reconsider an alternative theory of the QED with the photon as a massless vector Nambu-Goldstone boson and show that the underlying spontaneous Lorentz violation caused by the vector field vacuum expectation value, while being superficial in gauge invariant theory, becomes physically significant in the QED with a tiny gauge non-invariance. This leads, through special dispersion relations appearing for charged fermions, to a new class of phenomena which could be of distinctive observational interest in particle physics and astrophysics. They include a significant change in the GZK cutoff for UHE cosmic-ray nucleons, stability of high-energy pions and W bosons, modification of nucleon beta decays, and some others.

hep-th↗