Browsing by ORCID "0000-0003-1218-0451"

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    Inflation in symmergent metric-Palatini gravity
    (Sissa, 2024-02-21) Bostan, Nilay; Karahan, Canan; Sargın, Ozan
    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 cO 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 cO. The parameter which measures the deviation from the mass degeneracy is dubbed ˆ α. The parameters, cO and ˆ α, of symmergent gravity convey the information about the fermion and boson balance in the matter (SM+BSM) sector in number and in mass, respectively. In our analysis, we have investigated the space of the symmergent parameters cO and ˆ α wherein they produce results that comply with the inflationary observables ns, r, and dns/dlnk. Wehaveshownthatthevacuumenergytogetherwiththequadraticcurvaturetermarising in the symmergent gravity prescription are capable of inflating the universe provided that the quadratic curvature coefficient cO is negative (which corresponds to fermion dominance in number in the matter sector) and the deviation from the mass degeneracy in the matter sector is minute for both boson mass dominance and fermion mass dominance cases.
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    Large Field Polynomial Inflation in R2 Gravity with non-minimal coupling: Palatini formalism
    (Türkiye Enerji, Nükleer ve Maden Araştırma Kurumu (TENMAK), 2024-10-11) Bostan,Nilay; Karahan, Canan; Sargın, Ozan
    In this paper, we employ the Palatini formalism to investigate the dynamics of large field inflation using a renormalizable polynomial inflaton potential in the context of quadratic gravity. Assuming instant reheating, we make a comparative analysis of Large Field Polynomial Inflation (LFPI). We first consider inflaton (i) minimally and (ii) nonminimally coupled to R gravity, and then we continue with inflaton (iii) minimally and (iv) non-minimally coupled to R + R2 gravity. We scan the parameter space for the inflationary predictions (ns and r) consistent with the Planck and BICEP/Keck 2018 results as well as the sensitivity forecast of the future CMB-S4 and depict the compliant regions in the ϕ0 −β plane where ϕ0 and β are two parameters of polynomial inflation model which control the saddle point of the potential and the flatness in that region respectively. Furthermore, for the polynomial potential, we display the behavior of the running of the spectral index αs ≡ dns/d ln k with respect to the spectral index ns itself for all the cases.