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Articles de revues sur le sujet "Interacting Bosons (two Spin State)"
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Quintero Angulo, G., A. Pérez Martínez, H. Pérez Rojas et D. Manreza Paret. « (Self-)Magnetized Bose–Einstein condensate stars ». International Journal of Modern Physics D 28, no 10 (juillet 2019) : 1950135. http://dx.doi.org/10.1142/s0218271819501359.
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We study magnetic field effects on the Equations-of-State (EoS) and the structure of Bose–Einstein Condensate (BEC) stars, i.e. a compact object composed by a gas of interacting spin-one bosons formed up by the pairing of two neutrons. To include the magnetic field in the thermodynamic description, we assume that particle–magnetic field and particle–particle interactions are independent. We consider two configurations for the magnetic field: one where it is constant and externally fixed, and another where it is produced by the bosons through self-magnetization. Stable configurations of self-magnetized and magnetized nonspherical BEC stars are studied using structure equations that describe axially symmetric objects. In general, the magnetized BEC stars are spheroidal, less massive and smaller than the nonmagnetic ones, being these effects more relevant at low densities. Nevertheless, star masses around two solar masses are obtained by increasing the strength of the boson–boson interaction. The inner magnetic field profiles of the self-magnetized BEC stars can be computed as a function of the equatorial radii. The values obtained for the core and surface magnetic fields are in agreement with those typically found in compact objects.
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Hamber, Herbert W., et Reiko Toriumi. « Composite leptons at the LHC ». Modern Physics Letters A 29, no 07 (7 mars 2014) : 1450034. http://dx.doi.org/10.1142/s0217732314500345.
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In some models of electroweak interactions the W and Z bosons are considered composites, made up of spin-[Formula: see text] subconstituents. In these models a spin-0 counterpart of the W and Z boson naturally appears, whose higher mass can be attributed to a particular type of hyperfine spin interaction among the various subconstituents. Recently, it has been argued that the scalar state could be identified with the newly discovered Higgs (H) candidate. Here, we use the known spin splitting between the W/Z and H states to infer, within the framework of a purely phenomenological model, the relative strength of the spin–spin interactions. The results are then applied to the lepton sector, and used to crudely estimate the relevant spin splitting between the two lowest states. Our calculations in many ways parallels what is done in the SU(6) quark model, where most of the spin splittings between the lowest lying baryon and meson states are reasonably well-accounted for a simple color hyperfine interaction, with constituent (color-dressed) quark masses.
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Ozansoy, A., V. Arı et V. Çetinkaya. « Search for Excited Spin-3/2 Neutrinos at LHeC ». Advances in High Energy Physics 2016 (2016) : 1–10. http://dx.doi.org/10.1155/2016/1739027.
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We study the potential of the nextepcollider, namely, LHeC, with two optionss=1.3 TeV ands=1.98 TeV, to search for excited spin-1/2 and spin-3/2 neutrinos. We calculate the single production cross-section of excited spin-1/2 and spin-3/2 neutrinos according to their effective currents describing their interactions between gauge bosons and SM leptons. We choose theν⋆→eWdecay mode of excited neutrinos andW→jjdecay mode ofW-boson for the analysis. We put some kinematical cuts for the final state detectable particles and plot the invariant mass distributions for signal and the corresponding backgrounds. In order to obtain accessible limits for excited neutrino couplings, we show thef-f′andciV-ciAcontour plots for excited spin-1/2 and excited spin-3/2 neutrinos, respectively.
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YANG, ZHENWEI, JIANPING CHENG et XIANGMING SUN. « SPIN INTERACTION EFFECTS ON MOMENTUM CORRELATIONS FOR IDENTICAL FERMIONS EMITTED IN RELATIVISTIC HEAVY-ION COLLISIONS ». Modern Physics Letters A 22, no 02 (20 janvier 2007) : 131–39. http://dx.doi.org/10.1142/s0217732307020920.
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The Hanbury-Brown and Twiss (HBT) effects predict a Bose–Einstein enhancement of the two-particle momentum correlations of identical bosons at small relative momentum. However, the parallel momentum correlations between identical fermions are less argued. The momentum correlations can be altered by many factors, among which the spin interaction effects are discussed in this paper. It is found that the spin interaction plays an important role on the momentum correlations of identical fermions. For spin triplet state, a full Fermi–Dirac suppression represents as expected. On the contrary, a fake Bose–Einstein enhancement shows up for spin singlet state. The measured momentum correlations of fermions could hence provide some hints of spin interactions between them if all other factors such as Coulomb interactions were removed. Spin interactions make it more complicated to extract physical information from momentum correlations between fermions.
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VORRATH, TILL, TOBIAS BRANDES et BERNHARD KRAMER. « DYNAMICS OF A LARGE-SPIN-BOSON SYSTEM IN THE STRONG COUPLING REGIME ». International Journal of Modern Physics B 17, no 28 (10 novembre 2003) : 5489–93. http://dx.doi.org/10.1142/s0217979203020624.
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We investigate collective effects of an ensemble of biased two-level systems interacting with a bosonic bath in the strong coupling regime. The two level systems are described by a large pseudo-spin J. An equation for the expectation value M(t) of the z-component of the pseudo spin is derived and solved numerically for an ohmic bath at T=0. In case of a large cut-off frequency of the spectral function, a Markov approximation is justified and an analytical solution is presented. We find that M(t) relaxes towards a highly correlated state with maximum value ±J for large times. However, this relaxation is extremely slow for most parameter values so as if the system was "frozen in" by interaction with the bosonic bath.
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LEMKE, E. H. « PHOTOPRODUCTION OF WEAK VECTOR BOSONS IN A SPINOR THEORY ». International Journal of Modern Physics A 08, no 22 (10 septembre 1993) : 3883–908. http://dx.doi.org/10.1142/s0217751x93001570.
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We put forward the hypothesis that the weak W boson be a compound of two 2-component Lorentz spinors. The resulting novel γWW vertex is no gauge field structure. Nevertheless, the Born amplitude of γγ→WLWL respects partial-wave unitarity. As in the Yang-Mills case, the amplitude consists of a direct term, a crossed term, and a sea-gull term, and no unobserved particles are to be involved to get the “good” high-energy behavior. This is due to an imaginary pseudoscalar γWW interaction term. Significant differences between angular distributions and total cross sections of the non-Abelian case and the case of the composite bosons are displayed. The unitarity constraint applied to the reaction γγ→WTWT leads to the prediction of the existence of a composite charged weak scalar Φ±. It constitutes the spin 0 state of the constituents forming W±. Furthermore, the existence of a second and heavy scalar-vector pair ω-X is predicted. These weak boson states are found to exclude the presence of a seagull graph. In the threshold region, the total cross section of γγ→WW in the compositeness case is smaller than in the non-Abelian case. In a broad intermediate energy region it can be larger. Upper unitarity mass-bounds are estimated. They suggest mΦ≈mw so that Φ± might be discovered by forthcoming experiments. The structure of the γΦW, γXW and γωW transition vertices can be inferred without making recourse to unitarity. However, unitarity requires that the mass relation mΦ/mW=mω/mX be valid.
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KOTA, V. K. B. « TWO-BODY ENSEMBLES WITH GROUP SYMMETRIES FOR CHAOS AND REGULAR STRUCTURES ». International Journal of Modern Physics E 15, no 08 (novembre 2006) : 1869–83. http://dx.doi.org/10.1142/s0218301306005241.
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The simplest of the two-body random matrix ensembles (TBRE) is the embedded Gaussian orthogonal ensemble of two-body interactions [EGOE(2)] for spinless fermion systems. With m fermions in N single particle states, EGOE(2) and similarly EGUE(2) [the embedded Gaussian unitary ensemble] are generated by the SU(N) algebra. For these ensembles results, obtained using SU(N) Wigner-Racah algebra, for lower order cross correlations between spectra with different particle numbers are given. For fermions with spin degree of freedom one has EGOE(2)-s and similarly EGUE(2)-s, both generated by U(2Ω) ⊃ U(Ω) ⊗ SU(2) algebra with SU(2) generating m particle spins S and 2Ω = N. For these ensembles numerical and first analytical results for cross correlations between spectra with different particle numbers and spins are given. As further extensions, it is possible to construct EGOE(2)-(s,p) generated by U(2Ω) ⊃ [U(Ω) ⊃ SO(Ω)] ⊗ SU(2) where SO(Ω) corresponds to pairing, for nuclear shell model the EGOE(2)-JT generated by U(N) ⊃ SOJ(3) ⊗ SUT(2) algebra etc. On the other hand EGOE's with extended group symmetries of the shell model and the interacting boson models of nuclei, in particular via trace propagation for energy centroids give new insights into regular structures seen in the ground state region of nuclei. Several new examples for energy centroids generated by random 2 and 3-body interactions are given.
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BARENTZEN, HEINZ, et VIKTOR OUDOVENKO. « A SELF-CONSISTENT ANALYTIC THEORY OF THE SPIN BIPOLARON IN THE t–J MODEL ». International Journal of Modern Physics B 14, no 08 (30 mars 2000) : 809–35. http://dx.doi.org/10.1142/s0217979200000674.
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The spin bipolaron in the t–J model, i.e., two holes interacting with an antiferromagnetic spin background, is treated by an extension of the self-consistent Born approximation (SCBA), which has proved to be very accurate in the single-hole (spin polaron) problem. One of the main ingredients of our approach is the exact form of the bipolaron eigenstates in terms of a complete set of two-hole basis vectors. This enables us to eliminate the hole operators and to obtain the eigenvalue problem solely in terms of the boson (magnon) operators. The eigenvalue equation is then solved by a procedure similar to Reiter's construction of the single-polaron wave function in the SCBA. As in the latter case, the eigenvalue problem comprises a hierarchy of infinitely many coupled equations. These are brought into a soluble form by means of the SCBA and an additional decoupling approximation, whereupon the eigenvalue problem reduces to a linear integral equation involving the bipolaron self-energy. The numerical solutions of the integral equation are in quantitative agreement with the results of previous numerical studies of the problem. The d-wave bound state is found to have the lowest energy with a critical value J/t| c ≈ 0.4. In contrast to recent claims, we find no indication for a crossover between the d-wave and p-wave bound states.
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ADLER, STEPHEN L. « FERMION-SECTOR FRUSTRATED SU(4) AS A PREONIC PRECURSOR OF THE STANDARD MODEL ». International Journal of Modern Physics A 14, no 12 (10 mai 1999) : 1911–34. http://dx.doi.org/10.1142/s0217751x99000968.
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We give a model for composite quarks and leptons based on the semisimple gauge group SU(4), with the preons in the 10 representation; this choice of gauge gluon and preon multiplets is motivated by the possibility of embedding them in an N=6 supergravity multiplet, with the preons and antipreons both in the 20 of SU(6). Hypercolor singlets are forbidden in the fermionic sector of this theory; we propose that the SU(4) symmetry spontaneously breaks to SU (3)× U (1), with the binding of triality nonzero preons and gluons into composites, and with the formation of a color singlet condensate that breaks the initial Z12 vacuum symmetry to Z6. The spin ½ fermionic composites have the triality structure of a quark–lepton family, and the initial Z12 symmetry implies that there are six massless families, which mix to give three distinct families below the scale of the condensate. The spin 1 triality zero composites of the color triplet SU(4) gluons, when coupled to the condensate and with the color singlet representation of the 10 acting as a doorway state, lead to weak interactions of the fermionic composites through an SU(2) gauge algebra. The initial Z12 symmetry implies that this SU(2) gauge algebra structure is doubled, which in turn permits the corresponding independent gauge bosons to couple to chiral components of the composite fermions. Since the U(1) couples to the 10 representation as B-L, an effective SU (2)L× SU (2)R × U (1)B-L electroweak theory arises at the condensate scale, with all composites having the correct electric charge structure. Assuming a mechanism for forming composite Higgs bosons, the Z12→ Z6 symmetry breaking chain implies that below the condensate scale there can be two sets of discrete chiral Z6 triplets of Higgs doublets, as required by a phenomenological model for the CKM matrix that we have analyzed in detail elsewhere. A renormalization group analysis of the SU(4) model shows that the conversion by binding of one 10 of SU(4) to 12 triplets of SU(3) can give a very large, calculable hierarchy ratio between the SU(4) and the hadronic mass scales.
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Winterberg, F. « Substratum Approach to a Unified Theory of Elementary Particles ». Zeitschrift für Naturforschung A 43, no 12 (1 décembre 1988) : 1131–50. http://dx.doi.org/10.1515/zna-1988-1219.
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If special relativity is a dynamic symmetry caused by true physical deformations of bodies in absolute motion through a substratum or ether, the question if all interactions and elementary particles arc excitations of this ether must be raised. The ether being the cause of all the observed relativistic effects should then obey an exactly nonrelativistic law of motion, and which permits it to consist of positive and negative masses. The fundamental constants of nature, which according to Planck are 1) Newton's constant (G), 2) the velocity of light (c) and 3) Planck’s constant (ћ), suggest that the ether is made up of densely packed positive and negative Planck masses (Planckions), each with a diameter equaling the Planck length. Symmetry demands that the number of positive and negative Planck masses should be equal, making the cosmological constant equal to zero. Because the Planckions are nonrelativistic spin-zero bosons, the ether would therefore consist of two superfluids, one for the positive mass Planckions, and the other one for the negative mass Planckions. By spontaneous symmetry breaking this superfluid ether can in its ground state form a lattice of small vortex rings, with the vortex core radius equaling the Planck length. Force fields of massless vector gauge bosons can be interpreted as quantized transverse vortex waves propagating through this lattice. Because the smallest wave length would be about equal the ring radius of the circular vortices, the ring radius would assume the role of a unification scale. The ring radius is estimated to be about 103 times the Planck length, in fairly good agreement with the empirical evidence for the value of the grand unification scale of the standard model.Charge is explained by the zero point fluctuations of the Planckions attached to the vortex rings, wrhich thereby become the source of virtual phonons. Charge quantization is explained as the result of circulation quantization. Spinors result from bound states of the positive and negative masses of the substratum, and special relativity as a dynamic symmetry would be valid for all those objects. Quantum electrodynamics is derived as a low energy approximationIf spinors are made up from the positive and negative masses of the vortex ring resonance energy, whereby the spinors would assume the character of excitons, the spinor mass can be computed in terms of the Planck mass. Vice versa, with the lowest quark mass m given, a value for the gravitational constant in terms of m, ћ, and c can be obtained. The existence of different particle families can be understood by internal excitations of the spinors, and parity violation may find its explanation in a small nonzero vorticity of the ether. Bacause of its simple fundamental symmetry the theory is unique, it is always finite and has no anomalies.In the proposed theory all fields and interactions are explained in a completely mechanistic way by the Planck masses and their contact interactions. With special relativity as a derived dynamic symmetry and space remaining euclidean, the proposed approach can be seen as an alternative to Einstein’s program to explain all fields and their interactions by symmetries and singularities of a noneuclidean spacetime manifold.In Part I, the fundamental equation for the substratum, which has the form of a nonrelativistic nonlinear Heisenberg equation, is formulated. It is shown how it leads to a Maxwell-type set of equations for the gauge bosons. In Part II, Dirac-type spinors and quantum electrodynamics are derived. These results are then applied to obtain the lowest quark mass in terms of the Planck mass.
Livres sur le sujet "Interacting Bosons (two Spin State)"
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Glazov, M. M. Electron & ; Nuclear Spin Dynamics in Semiconductor Nanostructures. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198807308.001.0001.
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In recent years, the physics community has experienced a revival of interest in spin effects in solid state systems. On one hand, solid state systems, particularly semicon- ductors and semiconductor nanosystems, allow one to perform benchtop studies of quantum and relativistic phenomena. On the other hand, interest is supported by the prospects of realizing spin-based electronics where the electron or nuclear spins can play a role of quantum or classical information carriers. This book aims at rather detailed presentation of multifaceted physics of interacting electron and nuclear spins in semiconductors and, particularly, in semiconductor-based low-dimensional structures. The hyperfine interaction of the charge carrier and nuclear spins increases in nanosystems compared with bulk materials due to localization of electrons and holes and results in the spin exchange between these two systems. It gives rise to beautiful and complex physics occurring in the manybody and nonlinear system of electrons and nuclei in semiconductor nanosystems. As a result, an understanding of the intertwined spin systems of electrons and nuclei is crucial for in-depth studying and control of spin phenomena in semiconductors. The book addresses a number of the most prominent effects taking place in semiconductor nanosystems including hyperfine interaction, nuclear magnetic resonance, dynamical nuclear polarization, spin-Faraday and -Kerr effects, processes of electron spin decoherence and relaxation, effects of electron spin precession mode-locking and frequency focusing, as well as fluctuations of electron and nuclear spins.
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Kenyon, Ian R. Quantum 20/20. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198808350.001.0001.
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This text reviews fundametals and incorporates key themes of quantum physics. One theme contrasts boson condensation and fermion exclusivity. Bose–Einstein condensation is basic to superconductivity, superfluidity and gaseous BEC. Fermion exclusivity leads to compact stars and to atomic structure, and thence to the band structure of metals and semiconductors with applications in material science, modern optics and electronics. A second theme is that a wavefunction at a point, and in particular its phase is unique (ignoring a global phase change). If there are symmetries, conservation laws follow and quantum states which are eigenfunctions of the conserved quantities. By contrast with no particular symmetry topological effects occur such as the Bohm–Aharonov effect: also stable vortex formation in superfluids, superconductors and BEC, all these having quantized circulation of some sort. The quantum Hall effect and quantum spin Hall effect are ab initio topological. A third theme is entanglement: a feature that distinguishes the quantum world from the classical world. This property led Einstein, Podolsky and Rosen to the view that quantum mechanics is an incomplete physical theory. Bell proposed the way that any underlying local hidden variable theory could be, and was experimentally rejected. Powerful tools in quantum optics, including near-term secure communications, rely on entanglement. It was exploited in the the measurement of CP violation in the decay of beauty mesons. A fourth theme is the limitations on measurement precision set by quantum mechanics. These can be circumvented by quantum non-demolition techniques and by squeezing phase space so that the uncertainty is moved to a variable conjugate to that being measured. The boundaries of precision are explored in the measurement of g-2 for the electron, and in the detection of gravitational waves by LIGO; the latter achievement has opened a new window on the Universe. The fifth and last theme is quantum field theory. This is based on local conservation of charges. It reaches its most impressive form in the quantum gauge theories of the strong, electromagnetic and weak interactions, culminating in the discovery of the Higgs. Where particle physics has particles condensed matter has a galaxy of pseudoparticles that exist only in matter and are always in some sense special to particular states of matter. Emergent phenomena in matter are successfully modelled and analysed using quasiparticles and quantum theory. Lessons learned in that way on spontaneous symmetry breaking in superconductivity were the key to constructing a consistent quantum gauge theory of electroweak processes in particle physics.
Chapitres de livres sur le sujet "Interacting Bosons (two Spin State)"
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Nitzan, Abraham. « The Spin–Boson Model ». Dans Chemical Dynamics in Condensed Phases. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780198529798.003.0018.
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In a generic quantum mechanical description of a molecule interacting with its thermal environment, the molecule is represented as a few level system (in the simplest description just two, for example, ground and excited states) and the environment is often modeled as a bath of harmonic oscillators. The resulting theoretical framework is known as the spin–boson model, a term that seems to have emerged in the Kondo problem literature (which deals with the behavior of magnetic impurities in metals) during the 1960s, but is now used in a much broader context. Indeed, it has become one of the central models of theoretical physics, with applications in physics, chemistry, and biology that range far beyond the subject of this book. Transitions between molecular electronic states coupled to nuclear vibrations, environmental phonons, and photon modes of the radiation field fall within this class of problems. The present chapter discusses this model and some of its mathematical implications. The reader may note that some of the subjects discussed in Chapter 9 are reiterated here in this more general framework. In Sections 2.2 and 2.9 we have discussed the dynamics of the two-level system and of the harmonic oscillator, respectively. These exactly soluble models are often used as prototypes of important classes of physical system. The harmonic oscillator is an exact model for a mode of the radiation field and provides good starting points for describing nuclear motions in molecules and in solid environments. It can also describe the short-time dynamics of liquid environments via the instantaneous normal mode approach. In fact, many linear response treatments in both classical and quantum dynamics lead to harmonic oscillator models: Linear response implies that forces responsible for the return of a system to equilibrium depend linearly on the deviation from equilibrium—a harmonic oscillator property! We will see a specific example of this phenomenology in our discussion of dielectric response in Section 16.9.
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Mota, Fernando, Juan J. Novoa et Joel S. Miller. « Long, Multicenter Bonds in Radical Anion π-dimers ». Dans Intermolecular Interactions in Crystals : Fundamentals of Crystal Engineering, 595–613. The Royal Society of Chemistry, 2017. http://dx.doi.org/10.1039/bk9781782621737-00595.
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Long, multicenter C–C bonds (LMBs) are a new sub-class of bonds that can occur between a pair of neutral or charged radicals, and, similar to covalent bonds, result in a diamagnetic compound. LMBs were first established for the eclipsed, cofacial π-[TCNE]22− (TCNE=tetracyanoethylene). A systematic analysis of the properties of the long multicenter bond in the prototypical π-[TCNE]22− dimer, where the long, multicenter bond connects two radical anions, has been established by using high level ab initio methods. The results obtained show that LMBs share the most fundamental properties of intermolecular bonds (namely, their strength and equilibrium distance, their dependence on electrostatic and dispersion components). Additionally, they have a weak bonding component that provides characteristics of covalent bonds (namely, their origin results from the overlap of the orbitals of the interacting fragments, as well as their dependence on the spin multiplicity of the aggregate.) As a result, it is possible to talk about a n-electron m-centered intermolecular bonds, in a given state spin multiplicity. LMBs are not van der Waals bonds as they lack a bonding component. Also, they cannot be electrostatic bonds (due to the presence of an important bonding and dispersion components).
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Toroczkai, Zoltan, et György Korniss. « Scalability, Random Surfaces, and Synchronized Computing Networks ». Dans Computational Complexity and Statistical Physics. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780195177374.003.0020.
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In most cases, it is impossible to describe and understand complex system dynamics via analytical methods. The density of problems that are rigorously solvable with analytic tools is vanishingly small in the set of all problems, and often the only way one can reliably obtain a system-level understanding of such problems is through direct simulation. This chapter broadens the discussion on the relationship between complexity and statistical physics by exploring how the computational scalability of parallelized simulation can be analyzed using a physical model of surface growth. Specifically, the systems considered here are made up of a large number of interacting individual elements with a finite number of attributes, or local state variables, each assuming a countable number (typically finite) of values. The dynamics of the local state variables are discrete events occurring in continuous time. Between two consecutive updates, the local variables stay unchanged. Another important assumption we make is that the interactions in the underlying system to be simulated have finite range. Examples of such systems include: magnetic systems (spin states and spin flip dynamics); surface growth via molecular beam epitaxy (height of the surface, molecular deposition, and diffusion dynamics); epidemiology (health of an individual, the dynamics of infection and recovery); financial markets (wealth state, buy/sell dynamics); and wireless communications or queueing systems (number of jobs, job arrival dynamics). Often—as in the case we study here—the dynamics of such systems are inherently stochastic and asynchronous. The simulation of such systems is nontrivial, and in most cases the complexity of the problem requires simulations on distributed architectures, defining the field of parallel discrete-event simulations (PDES) [186, 367, 416]. Conceptually, the computational task is divided among n processing elements (PEs), where each processor evolves the dynamics of the allocated piece. Due to the interactions among the individual elements of the simulated system (spins, atoms, packets, calls, etc.) the PEs must coordinate with a subset of other PEs during the simulation. For example, the state of a spin can only be updated if the state of the neighbors is known. However, some neighbors might belong to the computational domain of another PE, thus, message passing will be required in order to preserve causality.
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Oomes, Nienke A. « Emerging Markets and Persistent Inequality in a Nonlinear Voting Model ». Dans New Constructions in Cellular Automata. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195137170.003.0014.
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Since it is one of the few spin systems that can be studied analytically, the Voter Model has been extensively discussed in the interacting particle systems literature. In the original interpretation of this model, voters choose their political positions with probabilities equal to the voting frequency of their friends. One of the main results is that, in one and two dimensions, the system clusters—i.e., converges to a homogeneous steady state—while heterogeneity can persist only in dimensions higher than two. This chapter develops an economic model that is similar to the Voter Model, in that agents decide between economic positions, conditional on the economic choices of their trade partners. The choices considered here are market production and nonmarket production, where the payoffs associated with market production for a given agent are a function of the amount of market goods produced by others. Intuitively, the more people are producing for the market, the more potential trade partners exist, hence the higher the expected payoff associated with market production. Similarly, the smaller the extent of the market, the lower the expected gains from trade, hence the smaller the incentive to produce for the market. When each agent is assumed to have an equal probability of trading with any other agent in his or.her trade network, the payoffs associated with market production are linearly increasing in the network’s total market output. However, this linearity in payoffs does not necessarily imply that the conditional probability of working for the market is linearly increasing in total market production, as the Voter Model would have it. As it turns out, this follows only if agents believe, mistakenly, that their trade partners will decide to work for the market with a probability that is exactly proportional to their current market output. Clearly, a more general approach is obtained by allowing for different types of expectations agents may have about the production decisions of their trade partners. A model that allows for such an approach is the so-called Nonlinear Voter Model (NLVM), studied by Molofsky et al.
Actes de conférences sur le sujet "Interacting Bosons (two Spin State)"
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Mulhall, D. « Randomly interacting bosons on two spin levels ». Dans PROCEEDINGS OF THE 43RD INTERNATIONAL CONFERENCE APPLICATIONS OF MATHEMATICS IN ENGINEERING AND ECONOMICS : (AMEE’17). Author(s), 2017. http://dx.doi.org/10.1063/1.5016138.
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Fukuzawa, T., S. Y. Kim, T. K. Gustafson, E. E. Haller et E. Yamada. « Anomalous Diffusion of Repulsive Bosons in a Two-Dimensional Random Potential ». Dans Quantum Optoelectronics. Washington, D.C. : Optica Publishing Group, 1997. http://dx.doi.org/10.1364/qo.1997.qthb.2.
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Two-dimensional (2D) bosons can undergo a Kosterlitz-Thouless transition[1], which does not involve macroscopic occupation of a single quantum state, but which can still result in superfluidity. In addition, strongly interacting bosons subject to a random potential can also exhibit superfluidity, as in the case of charged superfluidity that occurs in high-T c superconductors. Competition between the strength of the interaction and the degree of potential disorder are among the many complicated and competing factors which determine whether superfluidity is promoted or supressed in a Bose system[2]. Strong potential disorder forces bosons to localize and can result in an insulating Bose glass phase. Alternatively, repulsive interactions among bosons act to release them from their traps, to keep their inter-particle distances as uniform as the potential allows, and to arrange the flow direction. An appropriate interaction strength can thus promote superfluidity.
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Cano-Andrade, Sergio, Michael R. von Spakovsky et Gian Paolo Beretta. « Steepest-Entropy-Ascent Quantum Thermodynamic Non-Equilibrium Modeling of Decoherence of a Composite System of Two Interacting Spin-½ Systems ». Dans ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-63596.
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The equation of motion of steepest-entropy-ascent quantum thermodynamics (SEA-QT) was first postulated in the early 1980s with the intent of modeling the non-linear dynamic behavior encountered in nature, which the unitary (linear) dynamics of the Schrödinger-von Neumann equation cannot. The SEA-QT equation is used here to model the decoherence phenomenon between two distinguishable and indivisible elementary constituents of type spin–½ (e.g., quantum bits or qubits). The resulting set of non-linear, first-order differential equations is solved with a fourth-order-Runge-Kutta routine provided by Matlab®. The time evolution of the state of the composite system as well as that of the reduced and locally-perceived states of the two constituents are traced from an initial non-equilibrium state of the composite along its relaxation towards stable equilibrium at constant system energy. An entangled and generally coherent, initial non-equilibrium state of the composite quantum system is prepared using a heuristic approach, which consists of randomly and homogeneously generating an initial point on the Bloch sphere for each of the constituents and then using a weighted average of their projections to arrive at an initial state for the composite. Results show how the initial entanglement and coherence between the two spin–½ constituents are reduced during relaxation towards a state of stable equilibrium. When the two particles are non-interacting, the initial coherence is lost once stable equilibrium is reached. When they are interacting, the coherence in the final stable equilibrium state is only that due to the interaction.
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Bochove, E. J., et P. W. Milonni. « Radiative Momentum Transfer to Atoms by a Phase-Conjugate Mirror ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.pd8.
Texte intégralRésumé :
We demonstrate, by solution of the Heisenberg equations of motion of the pseudo-spin and momentum operators of a two-level atom interacting with a phase- conjugate mirror (PCM) and a quantized radiation field, that a force is exerted by the PCM on the ground state atom. The expression found for the force is F=gRA(P1-P2)pvn̂, where P1 and P2 are the ground and excited state occupation probabilities, A=Einstein A-coefficient, pv=photon momentum at resonance, R=PCM reflectivity, n̂=unit outward normal to the PCM, and g=an aperture factor (g=9/64 for a dipole parallel to the plane of the PCM and solid angle=Ω= 2╔) . This result has a simple physical interpretation in terms of vacuum fields that are conjugated or amplified by the PCM (1,2).
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Kuhl, J., E. J. Mayer, G. O. Smith, D. Bennhardt, T. Meier, A. Schulze, P. Thomas, R. Hey et K. Ploog. « Contributions of Bound and Unbound Two-Exciton States to the Nonlinear Optical Response of GaAs Quantum Wells ». Dans International Conference on Ultrafast Phenomena. Washington, D.C. : Optica Publishing Group, 1994. http://dx.doi.org/10.1364/up.1994.md.5.
Texte intégralRésumé :
The strong influence of exciton/exciton interaction on the nonlinear optical response of the 2D exciton in GaAs quantum wells has been demonstrated in several recent experimental studies. The theoretical model for the microscopic coupling mechanism is still the subject of controversy, however. In ref. [1], we have presented a model including a density dependent coupling between opposite spin excitons which assumes that the interaction results in a renormalization of the matrix elements, dephasing rates and energies of the transition from the single-exciton state to the two-exciton state with respect to the corresponding quantities for the single exciton transitions. In contrast, Wang et al. claim that all experimental observations are explained by a density induced dephasing rate and that biexciton states play no role [2]. Here we present a new 3-pulse degenerate-four-wave-mixing (DFWM) configuration which is able to differentiate between pure local field effects and biexcitonic contributions to the time-integrated signal. Experiments were performed on an almost homogeneously broadened GaAs/Al0.3Ga0.7As single QW (well width 20 nm, photoluminescence line 0.3 meV, homogenous linewidth 0.15 meV) in the backward reflection geometry. The sample was cooled to 10 K and excited by a sequence of three pulses (1.1 ps duration) with equal intensity, wave vectors k→1,k→2,k→3 and delays τ12 and τ13 between the second and first and the third and first pulse, respectively. The signal was monitored in the direction k→ s =k→1+k→2−k→3 which provides no signal for the chosen pulse length if local field and renormalization effects are negligible. The peak intensity of the time-integrated DFWM signal has been calculated by solving the optical Bloch for a system of two non-interacting two-level systems (2LS) with opposite circular polarization selection rules (local field effect) and for the renormalized four-level system (4LS) depicted in Fig. 1 which assumes the formation of biexcitons between excitons with opposite spins. The signal strength is proportional to the strength of the local field in the case of the 2LS and to the renormalization for the 4LS. The peak signal intensities expected for pure local field and pure biexction contributions are summarized in the second and third column of Table 1 for eight experimental configurations applying different linear and circularly polarized pulses. The values are normalized to the signal strength predicted for three parallel linearly polarized pulses. Close inspection of the data reveals remarkable differences of the peak amplitude with polarization geometry for the two coupling models.