Canan Nurhan Karahan

In this paper, we study the cosmological inflation phenomenon in symmergent gravity theory. Symmergent gravity is a novel framework which merges gravity and the standard model (SM) so that the gravity emerges from the matter loops and restores the broken gauge symmetries along the way. Symmergent gravity is capable of inducing the gravitational constant G and the quadratic curvature coefficient c O from the loop corrections of the matter sector in a flat space-time. In the event that all the matter fields, including the beyond the standard model (BSM) sector, are mass degenerate, the vacuum energy can be expressed in terms of G and c O. The parameter which measures the deviation from the mass degeneracy is dubbed hat alpha. The parameters, c O and hat alpha, of symmergent gravity convey the information about the fermion and boson balance in the matter (SM+ BSM) sector in number and in mass …

In view of various field-theoretic reasons, in the present work, we study the question of if the usual dimensional regularization can be extended to quantum field theories with an ultraviolet cutoff (Poincare-breaking scale) in a way that preserves all the properties of the dimensional regularization. And we find that it can indeed be achieved. The resulting extension gives a framework in which the power-law and logarithmic divergences get detached to involve different scales. This new regularization scheme, the detached regularization as we call it, enables one to treat the power-law and logarithmic divergences differently and independently. We apply the detached regularization to the computation of the vacuum energy and to two well-known quantum field theories, namely the scalar and spinor electrodynamics. As a case study, we consider Fujikawa's subtractive renormalization in the framework of the detached …

Recently proposed Type-3/2 seesaw mechanism is an alternative model to the Type-I seesaw. In this novel mechanism the light neutrino masses are induced via a vector-spinor, which keeps the Higgs mass stabilized at one loop. Here, in this letter, radiative corrections to the light neutrino masses via this vector spinor is studied. It is shown that the active neutrinos get trivial correction from the vector spinor loop as long as the mass of vector spinor is at the order of 2.8×10^12 GeV or higher. This is in agreement with the minimum mass value required for inducing active neutrino masses (M_ψ≈10^14 GeV) and naturalness criteria of Higgs field (M_ψ≈10^16 GeV) in Type-3/2 seesaw mechanism.

The Palatini gravitational action is enlarged by an arbitrary function f (X) of the determinants of the Ricci tensor and the metric, X=| det. R|/| det. g|. The resulting Ricci-determinant theory exhibits novel deviations from general relativity. We study a particular realization where the extension is characterized by the square-root of the Ricci determinant, f (X)= λ Edd X, which corresponds to the famous Eddington action. We analyze the obtained equations for perfect fluid source and show that the affine connection can be solved in terms of the energy density and pressure of the fluid through an obtained disformal metric. As an application, we derive the hydrostatic equilibrium equations for relativistic stars and inspect the significant effects induced by the square-root of the Ricci tensor. We find that an upper bound on λ Edd, at which deviations from the predictions of general relativity on neutron stars become prominent …

The type-I seesaw mechanism provides a natural explanation for tiny neutrino masses. The right-handed neutrino masses it requires are, however, too large to keep the Higgs boson mass at its measured value. We show that vector spinors, singlet leptons that are like right-handed neutrinos, generate tiny neutrino masses naturally through the exchange of spin-1/2 and spin-3/2 components. This one-step seesaw mechanism, which we call the type-3/2 seesaw, keeps the Higgs boson mass unchanged at one loop and gives cause therefore to no fine-tuning problem. If the on-shell vector spinor is a pure spin-3/2 particle, then it becomes a potential candidate for hidden dark matter which gets diluted due only to the expansion of the Universe. The type-3/2 seesaw provides a natural framework for the neutrino, Higgs boson, and dark matter sectors, with overall agreement with current experiments and observations.

The type-I seesaw mechanism provides a natural explanation for tiny neutrino masses. The right-handed neutrino masses it requires are, however, too large to keep the Higgs boson mass at its measured value. We show that vector spinors, singlet leptons that are like right-handed neutrinos, generate tiny neutrino masses naturally through the exchange of spin-1/2 and spin-3/2 components. This one-step seesaw mechanism, which we call the type-3/2 seesaw, keeps the Higgs boson mass unchanged at one loop and gives cause therefore to no fine-tuning problem. If the on-shell vector spinor is a pure spin-3/2 particle, then it becomes a potential candidate for hidden dark matter which gets diluted due only to the expansion of the Universe. The type-3/2 seesaw provides a natural framework for the neutrino, Higgs boson, and dark matter sectors, with overall agreement with current experiments and observations.

What is the luminosity needed for discovering new physics if the electroweak scale is to remain stable? In this work we study this question, with the pertinent example of a real singlet scalar which couples to the Higgs field at the renormalizable level. Observing that the electroweak scale remains stable if the two scalars couple in a see-sawic fashion through a mass-degeneracy-driven unification linkup among quartic couplings at a given scale, we show by detailed simulation studies of the channel that the HL-LHC, which is expected to deliver an integrated luminosity of , has no significant excess of signal over the background in the 800–2000 GeV mass range. The FCC-hh, on the other hand, can discover scalars up to a mass of 870 GeV with an integrated luminosity . Observation at (discovery at ) of a new scalar with a minimum mass 800 GeV requires at least  …

Since the current evidence of the existence of dark matter is revealed only through its gravitational influence, the way it couples to gravity must be then of primary importance. Here, unlike the standard model sector, which is typically coupled to a metric, dark matter is supposed to couple to a spacetime affine connection only through a Z 2-symmetry breaking term. We show that this structure leads to a coupling between dark matter, which is considered scalar, and the standard model Higgs potential. This induces dark matter decays into standard model particles through the Higgs boson, which acts as a portal between the visible and the dark sectors. We study thoroughly the resulting decay modes for various mass ranges and provide relevant bounds on the nonminimal coupling to affine gravity in line with observational data. Moreover, we find that the coupling to a Higgs boson can be sufficiently large to facilitate the …