M. Loewe | Pontificia Universidad Catolica de Chile (original) (raw)

Papers by M. Loewe

Alejandro Ayala, L. A. Hernández, M. Loewe, Alfredo Raya J. C. Rojas, R. Zamora Instituto de Cien... more Alejandro Ayala, L. A. Hernández, M. Loewe, Alfredo Raya J. C. Rojas, R. Zamora Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, México Distrito Federal 04510, Mexico. Centre for Theoretical and Mathematical Physics, and Department of Physics, University of Cape Town, Rondebosch 7700, South Africa. Instituto de F́ısica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile. Centro Cient́ıfico-Tecnológico de Valparáıso, Casilla 110-V, Valparáıso, Chile. Instituto de F́ısica y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio C-3, Ciudad Universitaria, Morelia, Michoacán 58040, Mexico. Departamento de F́ısica, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile, Instituto de Ciencias Basicas, Universidad Diego Portales, Casilla 298-V, Santiago, Chile, Centro de Investigación y Desarrollo en Ciencias Aeroespaciales (CIDCA), Fuerza Aérea de Chile, Santiago, Chile.

Nuclear and Particle Physics Proceedings, 2015

Physical Review D, 2009

Quantum fluctuations in the QED vacuum generate non-linear effects, such as peculiar induced elec... more Quantum fluctuations in the QED vacuum generate non-linear effects, such as peculiar induced electromagnetic fields. In particular, we show here that an electrically neutral particle, possessing a magnetic dipole moment, develops an induced electric dipole-type moment with unusual angular dependence, when immersed in a quasistatic, constant external electric field. The calculation of this effect is done in the framework of the Euler-Heisenberg effective QED Lagrangian, corresponding to the weak field asymptotic expansion of the effective action to one-loop order. It is argued that the neutron might be a good candidate to probe this signal of non-linearity in QED.

Journal of Physics A: Mathematical and General, 1990

... 560 M Loewe and M Sanhueza behaviour of the ground-state energy as a function of a. If ro dim... more ... 560 M Loewe and M Sanhueza behaviour of the ground-state energy as a function of a. If ro diminishes, a larger value of a is required to induce a bound state. ... [SI Gotfried K 1966 Quantum Mechanics (New York: Benjamin) Peccei RD 1988 A new phase for an old theory? ...

Nuclear Physics B - Proceedings Supplements, 2010

We present a modification of the standard method of evaluating the semihadronic tau decay width. ... more We present a modification of the standard method of evaluating the semihadronic tau decay width. The method is based on a derivative expansion for the Adler function rather than the standard series in powers of the strong coupling. The extracted QCD coupling at the tau mass scale is by 2% lower than the "contour improved" value. We find α s (M 2 Z) = 0.1211 ± 0.0010.

Nuclear Physics B - Proceedings Supplements, 2000

A thermal QCD Finite Energy Sum Rule (FESR) allows us to obtain the temperature dependence of the... more A thermal QCD Finite Energy Sum Rule (FESR) allows us to obtain the temperature dependence of the axial vector coupling of the nucleon, gA(T). It turns out that this coupling is essentially constant for the wide range 0 _< T < 0.9T~, being T~ the critical deconfining temperature. In contrast to other effective hadronic couplings, gA(T) diverges when T ~ Tc. At finite temperature, gA developes also a q2 dependence. This led us to explore the mean squared radius associated to gA, finding that it diverges at the critical temperature, thus signalling quark deconfinement. Finally, as a byproduct of our analysis, we study the thermal evolution of the Goldberger-Treiman relation.

For the lowest Landau level, noncommutative quantum mechanics and the Landau Hamiltonian are equi... more For the lowest Landau level, noncommutative quantum mechanics and the Landau Hamiltonian are equivalent theories. Using this fact, we find that the parameter that measures the noncommutative effects is given by θ = 4¯ h 2 c 2 eH 0. From this formula we can infer a numerical estimate for θ using the data for the magnetic field used in the quantum Hall effect (H 0 ∼ 12T) and we get that the θ = 0.6 nb. Note that this value corresponds to a typical cross section in neutrino interactions.

Modern Physics Letters A, 1994

In the scalar ɸ4 theory we discuss the behavior of the thermal four-point amplitude, after making... more In the scalar ɸ4 theory we discuss the behavior of the thermal four-point amplitude, after making a resumation of an infinite chain of loops. The calculation is presented in the thermofield dynamics formalism. It is shown that the zero temperature contribution to the real part of the amplitude has no differences with respect to the usual one-loop result. This is not the case, however, for the temperature-dependent part, where the loop resumation implies a completely different behavior of the amplitude, for the real as well as for the imaginary parts, compared to the one-loop result.

Zeitschrift f�r Physik C: Particles and Fields, 1993

It is shown, to leading order in the virial expansion, that unitarity of the rcn scattering ampli... more It is shown, to leading order in the virial expansion, that unitarity of the rcn scattering amplitude implies that if the p-meson width Fp(T) increases with temperature, then the p-meson mass Mp(T) must also increase. The temperature dependence of Mp(T) is explicitly obtained from a simple, but physically motivated, parametrization of the I = J = 1 nn scattering amplitude.

Physical Review D, 1985

We calculate light-quark mass differences in the framework of the Laplace-transform QCD sum rules... more We calculate light-quark mass differences in the framework of the Laplace-transform QCD sum rules using an improved parametrization of the hadronic spectral functions. Our results are (tn,m"}~|o,v-185+15 MeV and (mdm")~1 o, v=4+1 MeV. Using an earlier determination of the quark-mass sums based on similar techniques, these results lead to: m"(1 GeV) =6+1 MeV, md(1 GeV) =10+I MeV, and m, (1 GeV) =192+15 MeV. Next, we estimate the difference of the light-quark vacuum condensates in the framework of the Laplace-transform QCD sum rules. Our results are g(0}'"=-{0-3.5}X10 GeV and g(0}""=-(0-2.4)X 10 GeV", where /{0}; are the renormalization-group-invariant quantities li(0};=-(mJm;) (pjpi p;f;).-These values imply a small flavor symmetry breaking in the QCD nonperturbative vacuum, i.e. , (ss)/(uu) =0.9+0.1 and 1-(dd) /(uu) =(0-6) X 10

Physics Letters B, 1997

A Finite Energy QCD sum rule at non-zero temperature is used to determine the q 2-and the T-depen... more A Finite Energy QCD sum rule at non-zero temperature is used to determine the q 2-and the T-dependence of the ρππ vertex function in the space-like region. A comparison with an independent QCD determination of the electromagnetic pion form factor F π at T = 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 ρππ (q 2 , T) vanishes at the critical temperature T c , independently of q 2. Also, by extrapolating the ρππ form factor to q 2 = 0, it is found that the pion radius increases with increasing T , and it diverges at T = T c .

Nuclear Physics B - Proceedings Supplements, 2009

The renormalizable Abelian quantum field theory model of Kroll, Lee, and Zumino is used at the on... more The renormalizable Abelian quantum field theory model of Kroll, Lee, and Zumino is used at the one loop level to compute vertex corrections to the tree-level, Vector Meson Dominance (VMD) electromagnetic pion form factor. These corrections, together with the one-loop vacuum polarization contribution, imply a resulting electromagnetic pion form factor in excellent agreement with data in the whole range of accessible momentum transfers in the space-like region. The time-like form factor, which reproduces the Gounaris-Sakurai formula at and near the rho-meson peak, is unaffected by the vertex correction at order O(g 2). The KLZ model is also used to compute the scalar radius of the pion at the one loop level, finding r 2 π S = 0.40f m 2. This value implies for the low energy constant of chiral perturbation theoryl 4 = 3.4.

Physics Letters B, 1994

The University of Cape Town has been given the right to re?toduce this thesis in whole or In part... more The University of Cape Town has been given the right to re?toduce this thesis in whole or In part. Copyright is held by the author.

AIP Conference Proceedings, 2010

At the one loop level, we make use of the renormalizable Abelian quantum field theory model of Kr... more At the one loop level, we make use of the renormalizable Abelian quantum field theory model of Kroll, Lee, and Zumino (KLZ) in order to compute the vertex corrections to the tree-level, Vector Meson Dominance (VMD) electromagnetic pion form factor. This result, together with the one-loop vacuum polarization contribution, implies an electromagnetic pion form factor which is in outstanding agreement with data in the whole range of accessible momentum transfers in the space-like region. The time-like form factor, which reproduces the Gounaris-Sakurai formula at and near the rho-meson peak, remains unaffected by the vertex correction at order (g2). We also use the KLZ model to compute the pion scalar radius at the one loop level, finding <rpi2>S = 0.40 fm2. From this value we find for the low energy constant of chiral perturbation theory l4 = 3.4.

Physics Letters B, 1996

The temperature corrections to the current algebra Gell-Mann, Oakes, and Renner (GMOR) relation i... more The temperature corrections to the current algebra Gell-Mann, Oakes, and Renner (GMOR) relation in SU (2) ⊗ SU (2) are investigated in the framework of QCD sum rules. There are no corrections at leading order in the quark masses. At the next to leading order we find corrections of the form m 2 q T 2 , which are small except near the critical temperature. As a by-product we obtain the temperature behaviour of the pion mass, which is essentially constant, except near the critical temperature where it increases with T .

Physics Letters B, 2000

A thermal Finite Energy QCD Sum Rule is used to determine the temperature behaviour of the ωρπ st... more A thermal Finite Energy QCD Sum Rule is used to determine the temperature behaviour of the ωρπ 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 π 0 → γγ amplitude, which is also found to vanish at the critical temperature, as expected. This result supports the validity of VMD at T = 0. However, if VMD would not hold at finite temperature, then there is no prediction for the π 0 → γγ amplitude.

Physical Review D, 2010

The semihadronic tau decay width allows a clean extraction of the strong coupling constant at low... more The semihadronic tau decay width allows a clean extraction of the strong coupling constant at low energies. We present a modification of the standard "contour improved" method based on a derivative expansion of the Adler function. The new approach has some advantages compared to contour improved perturbation theory. The renormalization scale dependence is weaker by more than a factor two and the last term of the expansion is reduced by about 10%, while the renormalization scheme dependence remains approximately equal. The extracted QCD coupling at the tau mass scale is by 2% lower than the "contour improved" value. We find αs(M 2 Z) = 0.1211 ± 0.0010.

Physical Review D, 2011

The real time formalism at finite temperature and chemical potential for the nonlocal Nambu-Jona-... more The real time formalism at finite temperature and chemical potential for the nonlocal Nambu-Jona-Lasinio model is developed in the presence of a Gaussian covariant regulator. We construct the most general thermal propagator, by means of the spectral function. As a result, the model involves the propagation of massive quasiparticles. The appearance of complex poles is interpreted as a confinement signal, and, in this case, we have unstable quasiparticles with a finite decay width. An expression for the propagator along the critical line, where complex poles start to appear, is also obtained. A generalization to other covariant regulators is proposed.