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Citation - WoS: 6
Citation - Scopus: 6
Bound Free Electron-Positron Pair Production Accompanied by Giant Dipole Resonances
(Amer Physical Soc., 2011) Şengül, Metin Y.; Guclu, Mehmet C.
At the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) for example virtual photons produce many particles. At small impact parameters where the colliding nuclei make peripheral collisions photon fluxes are very large and these are responsible for the multiple photonuclear interactions. Free pair productions bound free pair productions and nuclear Coulomb excitations are important examples of such interactions and these processes play important roles in the beam luminosity at RHIC and LHC. Here we obtained the impact parameter dependence of bound free pair production cross sections and by using this probability we obtained bound free electron-positron pair production with nuclear breakup for heavy ion collisions at RHIC and LHC. We also compared our results to the other calculations.
Citation - WoS: 12
Citation - Scopus: 10
Bound-Free Electron-Positron Pair Production in Relativistic Heavy-Ion Collisions
(Amer Physical Soc., 2009) Şengül, Metin Y.; Güçlü, Mehmet C.; Fritzsche, S.
The bound-free electron-positron pair production is considered for relativistic heavy ion collisions. In particular cross sections are calculated for the pair production with the simultaneous capture of the electron into the 1s ground state of one of the ions and for energies that are relevant for the relativistic heavy ion collider and the large hadron colliders. In the framework of perturbation theory we applied Monte Carlo integration techniques to compute the lowest-order Feynman diagrams amplitudes by using Darwin wave functions for the bound states of the electrons and Sommerfeld-Maue wave functions for the continuum states of the positrons. Calculations were performed especially for the collision of Au+Au at 100 GeV/nucleon and Pb+Pb at 3400 GeV/nucleon.
Citation - WoS: 3
Citation - Scopus: 2
Coulomb Corrections in the Lepton-Pair Production in Ultrarelativistic Nuclear Collisions
(Amer Physical Soc., 2005) Güçlu, Mehmet C.; Kovankaya, G.; Yılmaz, Melek
We solve the perturbative electron-positron pair production exactly by calculating the second-order Feynman diagrams. We compare our result with Born methods that include Coulomb corrections. We find that a small-momentum approximation is not adequate to obtain exact Coulomb corrections and higher-order terms should also be included. We also compare the impact parameter dependence cross sections.
Citation - WoS: 51
Citation - Scopus: 55
Crossover From Vibrational To Rotational Collectivity in Heavy Nuclei in the Shell-Model Monte Carlo Approach
(Amer Physical Soc., 2013) Özen, Cem; Alhassid, Yoram; Nakada, Hitoshi
Heavy nuclei exhibit a crossover from vibrational to rotational collectivity as the number of neutrons or protons increases from shell closure towards midshell but the microscopic description of this crossover has been a major challenge. We apply the shell model Monte Carlo approach to families of even-even samarium and neodymium isotopes and identify a microscopic signature of the crossover from vibrational to rotational collectivity in the low-temperature behavior of < J(2)>(T) where J is the total spin and T is the temperature. This signature agrees well with its values extracted from experimental data. We also calculate the state densities of these nuclei and find them to be in very good agreement with experimental data. Finally we define a collective enhancement factor from the ratio of the total state density to the intrinsic state density as calculated in the finite-temperature Hartree-Fock-Bogoliubov approximation. The decay of this enhancement factor with excitation energy is found to correlate with the pairing and shape phase transitions in these nuclei. DOI: 10.1103/PhysRevLett.110.042502
Citation - WoS: 11
Citation - Scopus: 11
Devil's Staircase Continuum in the Chiral Clock Spin Glass With Competing Ferromagnetic-Antiferromagnetic and Left-Right Chiral Interactions
(Amer Physical Soc., 2017) Caglar, Tolga; Berker, A. Nihat
The chiral clock spin-glass model with q = 5 states with both competing ferromagnetic-antiferromagnetic and left-right chiral frustrations is studied in d = 3 spatial dimensions by renormalization-group theory. The global phase diagram is calculated in temperature antiferromagnetic bond concentration p random chirality strength and right-chirality concentration c. The system has a ferromagnetic phase a multitude of different chiral phases a chiral spin-glass phase and a critical (algebraically) ordered phase. The ferromagnetic and chiral phases accumulate at the disordered phase boundary and form a spectrum of devil's staircases where different ordered phases characteristically intercede at all scales of phase-diagram space. Shallow and deep reentrances of the disordered phase bordered by fragments of regular and temperature-inverted devil's staircases are seen. The extremely rich phase diagrams are presented as continuously and qualitatively changing videos.
Citation - WoS: 14
Citation - Scopus: 14
Lower Lower-Critical Spin-Glass Dimension From Quenched Mixed-Spatial Spin Glasses
(Amer Physical Soc., 2018) Atalay, Bora; Berker, A. Nihat
By quenched-randomly mixing local units of different spatial dimensionalities we have studied Ising spin-glass systems on hierarchical lattices continuously in dimensionalities 1 <= d <= 3. The global phase diagram in temperature antiferromagnetic bond concentration and spatial dimensionality is calculated. We find that as dimension is lowered the spin-glass phase disappears to zero temperature at the lower-critical dimension d(c) = 2.431. Our system being a physically realizable system this sets an upper limit to the lower-critical dimension in general for the Ising spin-glass phase. As dimension is lowered towards d(c) the spin-glass critical temperature continuously goes to zero but the spin-glass chaos fully subsists to the brink of the disappearance of the spin-glass phase. The Lyapunov exponent measuring the strength of chaos is thus largely unaffected by the approach to d and shows a discontinuity to zero at d(c.)
Citation - WoS: 2
Citation - Scopus: 2
Maximally Random Discrete-Spin Systems With Symmetric and Asymmetric Interactions and Maximally Degenerate Ordering
(Amer Physical Soc., 2018) Atalay, Bora; Berker, A. Nihat
Discrete-spin systems with maximally random nearest-neighbor interactions that can be symmetric or asymmetric ferromagnetic or antiferromagnetic including off-diagonal disorder are studied for the number of states q = 34 in d dimensions. We use renormalization-group theory that is exact for hierarchical lattices and approximate (Migdal-Kadanoff) for hypercubic lattices. For all d > 1 and all nonmfimte temperatures the system eventually renormalizes to a random single state thus signaling q x q degenerate ordering. Note that this is the maximally degenerate ordering. For high-temperature initial conditions the system crosses over to this highly degenerate ordering only after spending many renormalization-group iterations near the disordered (infinite-temperature) fixed point. Thus a temperature range of short-range disorder in the presence of long-range order is identified as previously seen in underfrustrated Ising spin-glass systems. The entropy is calculated for all temperatures behaves similarly for ferromagnetic and antiferromagnetic interactions and shows a derivative maximum at the short-range disordering temperature. With a sharp immediate contrast of infinitesimally higher dimension 1 + epsilon the system is as expected disordered at all temperatures for d = 1.
Citation - WoS: 20
Citation - Scopus: 21
Multifaceted Dynamics of Janus Oscillator Networks
(Amer Physical Soc., 2019) Nicolaou, Zachary G.; Eroğlu, Deniz; Motter, Adilson E.
Recent research has led to the discovery of fundamental new phenomena in network synchronization including chimera states explosive synchronization and asymmetry-induced synchronization. Each of these phenomena has thus far been observed only in systems designed to exhibit that one phenomenon which raises the questions of whether they are mutually compatible and if so under what conditions they co-occur. Here we introduce a class of remarkably simple oscillator networks that concurrently exhibit all of these phenomena. The dynamical units consist of pairs of nonidentical phase oscillators which we refer to as Janus oscillators by analogy with Janus particles and the mythological figure from which their name is derived. In contrast to previous studies these networks exhibit (i) explosive synchronization with identical oscillators, (ii) extreme multistability of chimera states including traveling intermittent and bouncing chimeras, and (iii) asymmetry-induced synchronization in which synchronization is promoted by random oscillator heterogeneity. These networks also exhibit the previously unobserved possibility of inverted synchronization transitions in which a transition to a more synchronous state is induced by a reduction rather than an increase in the coupling strength. These various phenomena are shown to emerge under rather parsimonious conditions and even in locally connected ring topologies which has the potential to facilitate their use to control and manipulate synchronization in experiments.
Citation - WoS: 12
Citation - Scopus: 12
Phase Transitions Between Different Spin-Glass Phases and Between Different Chaoses in Quenched Random Chiral Systems
(Amer Physical Soc., 2017) Çağlar, Tolga; Berker, A. Nihat
The left-right chiral and ferromagnetic-antiferromagnetic double-spin-glass clock model with the crucially even number of states q = 4 and in three dimensions d = 3 has been studied by renormalization-group theory. We find for the first time to our knowledge four spin-glass phases including conventional chiral and quadrupolar spin-glass phases and phase transitions between spin-glass phases. The chaoses in the different spin-glass phases and in the phase transitions of the spin-glass phases with the other spin-glass phases with the non-spin-glass ordered phases and with the disordered phase are determined and quantified by Lyapunov exponents. It is seen that the chiral spin-glass phase is the most chaotic spin-glass phase. The calculated phase diagram is also otherwise very rich including regular and temperature-inverted devil's staircases and reentrances.

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