Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 16Citation - Scopus: 16Riemann-Eddington Theory: Incorporating Matter, Degravitating the Cosmological Constant(American Physical Society, 2014) Demir, Durmuş AliHere we show that Eddington's pure affine gravity, when extended with Riemann curvature, leads to gravitational field equations that incorporate matter. This Riemanned Eddington gravity outfits a setup in which matter gravitates normally with Newton's constant but vacuum gravitates differently with an independent gravitational constant. This novel setup enables degravitation of the vacuum to observed level not by any fine-tuning but by a large hierarchy between its gravitational constant and its energy density. Remarkably, degravitation of the cosmological constant is local, causal and natural yet only empirical because the requisite degravitation condition is not predicted by the theory.Article Citation - WoS: 100Citation - Scopus: 81Search for Physics Beyond the Standard Model in Final States With a Lepton and Missing Transverse Energy in Proton-Proton Collisions at Root S = 8 Tev(American Physical Society, 2015) Demir, Durmuş Ali; Karapınar, GülerA search for new physics in proton-proton collisions having final states with an electron or muon and missing transverse energy is presented. The analysis uses data collected in 2012 with the CMS detector, at an LHC center-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of 19.7 fb(-1). No significant deviation of the transverse mass distribution of the charged lepton-neutrino system from the standard model prediction is found. Mass exclusion limits of up to 3.28 TeVat 95% confidence level for a W0-boson with the same couplings as that of the standard model W-boson are determined. Results are also derived in the framework of split universal extra dimensions, and exclusion limits on Kaluza-Klein Wd(KK)((2)) states are found. The final state with large missing transverse energy also enables a search for dark matter production with a recoiling W-boson, with limits set on the mass and the production cross section of potential candidates. Finally, limits are established for a model including interference between a left-handed W'-boson and the standard model W-boson and for a compositeness model.Article Citation - WoS: 315Citation - Scopus: 301Transverse-Momentum and Pseudorapidity Distributions of Charged Hadrons in Pp Collisions at Root √s=0.9 and 2.36 Tev(Springer Verlag, 2010) Karapınar, Güler; Demir, Durmuş AliMeasurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at root s = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN(ch)/d eta vertical bar(vertical bar eta vertical bar<0.5), are 3.48 +/- 0.02 (stat.) +/- 0.13 (syst.) and 4.47 +/- 0.04 (stat.) +/- 0.16 (syst.), respectively. The results at 0.9 TeV are in agreement with previous measurements and confirm the expectation of near equal hadron production in p<(p)over bar> and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date.Article Citation - WoS: 26Citation - Scopus: 26Induced Affine Inflation(American Physical Society, 2018) Azri, Hemza; Demir, Durmuş AliInduced gravity, metrical gravity in which gravitational constant arises from vacuum expectation value of a heavy scalar, is known to suffer from Jordan frame vs Einstein frame ambiguity, especially in inflationary dynamics. Induced gravity in affine geometry, as we show here, leads to an emergent metric and gravity scale, with no Einstein-Jordan ambiguity. While gravity is induced by the vacuum expectation value of the scalar field, nonzero vacuum energy facilitates generation of the metric. Our analysis shows that induced gravity results in a relatively large tensor-to-scalar ratio in both metrical and affine gravity setups. However, the fact remains that the induced affine gravity provides an ambiguity-free framework.Article Citation - WoS: 10Citation - Scopus: 12Statistical Approach To Tunneling Time in Attosecond Experiments(Academic Press Inc., 2017) Demir, Durmuş Ali; Güner, TuğrulTunneling, transport of particles through classically forbidden regions, is a pure quantum phenomenon. It governs numerous phenomena ranging from single-molecule electronics to donor–acceptor transition reactions. The main problem is the absence of a universal method to compute tunneling time. This problem has been attacked in various ways in the literature. Here, in the present work, we show that a statistical approach to the problem, motivated by the imaginary nature of time in the forbidden regions, lead to a novel tunneling time formula which is real and subluminal (in contrast to various known time definitions implying superluminal tunneling). In addition to this, we show explicitly that the entropic time formula is in good agreement with the tunneling time measurements in laser-driven He ionization. Moreover, it sets an accurate range for long-range electron transfer reactions. The entropic time formula is general enough to extend to the photon and phonon tunneling phenomena.Article Citation - WoS: 4Citation - Scopus: 4Hidden Spin-3/2 Field in the Standard Model(Springer Verlag, 2017) Demir, Durmuş Ali; Karahan, Canan; Korutlu, Beste; Sargın, OzanHere we show that a massive spin-3/2 field can hide in the SM spectrum in a way revealing itself only virtually. We study collider signatures and loop effects of this field, and determine its role in Higgs inflation and its potential as dark matter. We show that this spin-3/2 field has a rich linear collider phenomenology and motivates consideration of a neutrino–Higgs collider. We also show that the study of Higgs inflation, dark matter and dark energy can reveal more about the neutrino and dark sector. © 2017, The Author(s).Article Citation - WoS: 47Citation - Scopus: 42Affine Inflation(American Physical Society, 2017) Azri, Hemza; Demir, Durmuş AliAffine gravity, a gravity theory based on affine connection with no notion of metric, supports scalar field dynamics only if scalar fields have nonvanishing potential. The nonvanishing vacuum energy ensures that the cosmological constant is nonvanishing. It also ensures that the energy-momentum tensor of vacuum gives the dynamically generated metric tensor. We construct this affine setup and study primordial inflation in it. We study inflationary dynamics in affine gravity and general relativity, comparatively. We show that nonminimally coupled inflaton dynamics can be transformed into minimally coupled ones with a modified potential. We also show that there is one unique frame in affine gravity, as opposed to the Einstein and Jordan frames in general relativity. Future observations with higher accuracy may be able to test affine gravity.Article Citation - WoS: 2Citation - Scopus: 2Higgsed Stueckelberg Vector and Higgs Quadratic Divergence(Elsevier Ltd., 2015) Demir, Durmuş Ali; Karahan, Canan Nurhan; Korutlu, BesteHere we show that, a hidden vector field whose gauge invariance is ensured by a Stueckelberg scalar and whose mass is spontaneously generated by the Standard Model Higgs field contributes to quadratic divergences in the Higgs boson mass squared, and even leads to its cancellation at one-loop when Higgs coupling to gauge field is fine-tuned. In contrast to mechanisms based on hidden scalars where a complete cancellation cannot be achieved, stabilization here is complete in that the hidden vector and the accompanying Stueckelberg scalar are both free from quadratic divergences at one-loop. This stability, deriving from hidden exact gauge invariance, can have important implications for modeling dark phenomena like dark matter, dark energy, dark photon and neutrino masses. The hidden fields can be produced at the LHC.Article Citation - WoS: 14Citation - Scopus: 14Dark Matter From Conformal Sectors(Elsevier Ltd., 2014) Demir, Durmuş Ali; Frank, Mariana; Korutlu, BesteWe show that a conformal-invariant dark sector, interacting conformally with the Standard Model (SM) fields through the Higgs portal, provides a viable framework where cold dark matter (CDM) and invisible Higgs decays can be addressed concurrently. Conformal symmetry naturally subsumes the ℤ2 symmetry needed for stability of the CDM. It also guarantees that the weaker the couplings of the dark sector fields to the SM Higgs field, the smaller the masses they acquire through electroweak breaking. The model comfortably satisfies the bounds from Large Hadron Collider (LHC) and Planck Space Telescope (PLANCK 2013).Article Citation - WoS: 15Citation - Scopus: 16Effects of Curvature-Higgs Coupling on Electroweak Fine-Tuning(Elsevier Ltd., 2014) Demir, Durmuş AliIt is shown that nonminimal coupling between the Standard Model (SM) Higgs field and spacetime curvature, present already at the renormalizable level, can be fine-tuned to stabilize the electroweak scale against power-law ultraviolet divergences. The nonminimal coupling acts as an extrinsic stabilizer with no effect on the loop structure of the SM, if gravity is classical. This novel fine-tuning scheme, which could also be interpreted within Sakharov's induced gravity approach, works neatly in extensions of the SM involving additional Higgs fields or singlet scalars.