Browsing by Author "Loewe, M"

Now showing 1 - 7 of 7
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    Axial anomaly, vector meson dominance and π0 → γγ at finite temperature
    (2000) Dominguez, CA; Loewe, M
    A thermal Finite Energy QCD Sum Rule is used to determine the temperature behaviour of the omega rho pi strong coupling. This coupling decreases with increasing T and vanishes at the critical temperature, a likely signal for quark deconfinement. This is then used in the Vector Meson Dominance (VMD) expression for the pi(0) --> gamma gamma amplitude, which is also found to vanish at the critical temperature, as expected. This result supports the validity of VMD at T not equal 0. However, if VMD would not hold at finite temperature, then there is no prediction for the pi(0) --> gamma gamma amplitude. (C) 2000 Elsevier Science B.V. All rights reserved.
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    Finite density and temperature in hybrid bag models
    (1999) De Francia, M; Falomir, H; Loewe, M
    We introduce the chemical potential in a system of two-flavored massless fermions in a chiral bag, with an external Skyrmion, by imposing boundary conditions in the Euclidean time direction. We express the fermionic mean number in terms of a functional trace involving the Green function of the boundary value problem, which is studied analytically. Numerical evaluations for the fermionic number are presented. [S0556-2813(99)04310-1].
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    Massless fermions in a bag at finite density and temperature
    (1997) DeFrancia, M; Falomir, H; Loewe, M
    We introduce the chemical potential in a system of massless fermions in a bag by imposing boundary conditions in the Euclidean time direction. We express the fermionic mean number in terms of a functional trace involving the Green's function of the boundary value problem, which we study analytically. Numerical evaluations are made, and an application to a simple hadron model is discussed.
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    Noncommutative quantum mechanics
    (2002) Gamboa, J; Méndez, F; Loewe, M; Rojas, JC
    Quantum mechanics in a noncommutative plane is considered. For a general two-dimensional central field, we find that the theory can be perturbatively solved for large values of the noncommutative parameter (theta) and explicit expressions for the eigenstates and eigenvalues are given. The Green function is explicitly obtained and we show that it can be expressed as an infinite series. For polynomial type potentials, we found a smooth limit for small values of theta and for nonpolynomial ones this limit is necessarily abrupt. The Landau problem, as a limit case of a noncommutative system, is also considered.
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    Quantum theory of tensionless noncommutative p-branes -: art. no. 106006
    (2004) Gamboa, J; Loewe, M; Méndez, F
    The quantum theory involving noncommutative tensionless p-branes is studied following path integral methods. Our procedure allows a simple treatment for generally covariant noncommutative extended systems and it contains, as a particular case, the thermodynamics and the quantum tensionless string theory. The effect induced by noncommutativity in the field space is to produce a confinement among pairing of null p-branes.
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    Testing spatial noncommutativity via the Aharonov-Bohm effect -: art. no. 045018
    (2002) Falomir, H; Gamboa, J; Loewe, M; Méndez, F; Rojas, JC
    The possibility of detecting noncommutative space relics is analyzed using the Aharonov-Bohm effect. We show that, if space is noncommutative, the holonomy receives nontrivial kinematical corrections that will produce a diffraction pattern even when the magnetic flux is quantized. The scattering problem is also formulated, and the differential cross section is calculated. Our results can be extrapolated to high energy physics and the bound thetasimilar to[10 TeV](-2) is found. If this bound holds, then noncommutative effects could be explored in scattering experiments measuring differential cross sections for small angles. The bound state Aharonov-Bohm effect is also discussed.
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    Vector meson dominance and g(rho pi pi) at finite temperature from QCD sum rules
    (1997) Dominguez, CA; Fetea, MS; Loewe, M
    A Finite Energy QCD sum rule at non-zero temperature is used to determine the q(2)- and the T-dependence of the rho pi pi vertex function in the space-like region, A comparison with an independent QCD determination of the electromagnetic pion form factor F-pi at T not equal 0 indicates that Vector Meson Dominance holds to a very good approximation at finite temperature. At the same time, analytical evidence for deconfinement is obtained from the result that g(rho pi pi)(q(2),T) vanishes at the critical temperature T-c, independently of q(2). Also, by extrapolating the rho pi pi form factor to q(2) = 0, it is found that the pion radius increases with increasing T, and it diverges at T = T-c. (C) 1997 Elsevier Science B.V.