22 results on '"de Carvalho, C. A. A."'
Search Results
2. Negative refraction and rotons in the relativistic Bose gas
- Author
-
Reis, D. M., Cavalcanti, S. B., and de Carvalho, C. A. A.
- Subjects
Condensed Matter - Quantum Gases ,High Energy Physics - Theory - Abstract
We investigate the dispersion of a classical electromagnetic field in a relativistic ideal gas of charged bosons using scalar quantum electrodynamics at finite temperature and charge density. We derive the effective electromagnetic responses and the electromagnetic propagation modes that characterize the gas as a left-handed material with negative effective index of refraction $n_{\rm eff}=-1$ below the transverse plasmon frequency. In the condensed phase, we show that the longitudinal plasmon dispersion relation exhibits a roton-type local minimum that disappears at the transition temperature., Comment: 6 pages, 5 figures
- Published
- 2020
- Full Text
- View/download PDF
3. The relativistic electron gas: a candidate for nature's left-handed material
- Author
-
de Carvalho, C. A. A.
- Subjects
Quantum Physics ,Condensed Matter - Other Condensed Matter ,High Energy Physics - Theory - Abstract
The electric permittivities and magnetic permeabilities for a relativistic electron gas are calculated from quantum electrodynamics at finite temperature and density as functions of temperature, chemical potential, frequency, and wavevector. The polarization and the magnetization depend linearly on both electric and magnetic fields, and are the sum of a zero-temperature and zero-density vacuum part with a temperature- and chemical potential-dependent medium part. Analytic calculations lead to generalized expressions that depend on three scalar functions. In the nonrelativistic limit, results reproduce the Lindhard formula. In the relativistic case, and in the long wavelength limit, we obtain: i) for $\omega=0$, generalized susceptibilities that reduce to known nonrelativistic limits; ii) for $\omega \neq 0$, Drude-type responses at zero and at high temperatures. The latter implies that one may have both $\epsilon$ and $\mu$ simultaneously negative, a behavior characteristic of metamaterials. This unambiguously indicates that the relativistic electron plasma is one of nature's candidates for the realization of a negative index of refraction system. Moreover, Maxwell's equations in the medium yield the dispersion relation and the index of refraction of the electron plasma. Present results should be relevant for plasma physics, astrophysical observations, synchrotrons, and other environments with fast moving electrons., Comment: Submitted to PRD
- Published
- 2015
- Full Text
- View/download PDF
4. Effective potential in the BET formalism
- Author
-
Bessa, A., de Carvalho, C. A. A., Fraga, E. S., and Gelis, F.
- Subjects
High Energy Physics - Phenomenology ,High Energy Physics - Theory - Abstract
We calculate the one-loop effective potential at finite temperature for a system of massless scalar fields with quartic interaction $\lambda\phi^4$ in the framework of the boundary effective theory (BET) formalism. The calculation relies on the solution of the classical equation of motion for the field, and Gaussian fluctuations around it. Our result is non-perturbative and differs from the standard one-loop effective potential for field values larger than $T/\sqrt{\lambda}$., Comment: 10 pages, 3 figures
- Published
- 2011
- Full Text
- View/download PDF
5. Quantum statistical correlations in thermal field theories: boundary effective theory
- Author
-
Bessa, A., Brandt, F. T., de Carvalho, C. A. A., and Fraga, E. S.
- Subjects
High Energy Physics - Phenomenology ,High Energy Physics - Theory - Abstract
We show that the one-loop effective action at finite temperature for a scalar field with quartic interaction has the same renormalized expression as at zero temperature if written in terms of a certain classical field $\phi_c$, and if we trade free propagators at zero temperature for their finite-temperature counterparts. The result follows if we write the partition function as an integral over field eigenstates (boundary fields) of the density matrix element in the functional Schr\"{o}dinger field-representation, and perform a semiclassical expansion in two steps: first, we integrate around the saddle-point for fixed boundary fields, which is the classical field $\phi_c$, a functional of the boundary fields; then, we perform a saddle-point integration over the boundary fields, whose correlations characterize the thermal properties of the system. This procedure provides a dimensionally-reduced effective theory for the thermal system. We calculate the two-point correlation as an example., Comment: 13 pages, 1 figure
- Published
- 2010
- Full Text
- View/download PDF
6. Zero-mode analysis of quantum statistical physics
- Author
-
Bessa, A., de Carvalho, C. A. A., and Fraga, E. S.
- Subjects
Quantum Physics ,Condensed Matter - Statistical Mechanics ,High Energy Physics - Phenomenology ,High Energy Physics - Theory - Abstract
We present a unified formulation for quantum statistical physics based on the representation of the density matrix as a functional integral. We identify the stochastic variable of the effective statistical theory that we derive as a boundary configuration and a zero mode relevant to the discussion of infrared physics. We illustrate our formulation by computing the partition function of an interacting one-dimensional quantum mechanical system at finite temperature from the path-integral representation for the density matrix. The method of calculation provides an alternative to the usual sum over periodic trajectories: it sums over paths with coincident endpoints, and includes non-vanishing boundary terms. An appropriately modified expansion into Matsubara modes provides a natural separation of the zero-mode physics. This feature may be useful in the treatment of infrared divergences that plague the perturbative approach in thermal field theory., Comment: 9 pages, 5 figures
- Published
- 2008
- Full Text
- View/download PDF
7. Primitively divergent diagrams in $\kappa$-deformed scalar field with quartic self-interaction
- Author
-
Neves, M. J., de Carvalho, C. A. A., Farina, C., and Cougo-Pinto, M. V.
- Subjects
High Energy Physics - Theory - Abstract
We obtain the primitively divergent diagrams in $\kappa$-deformed scalar field in four-dimensional spacetime with quartic self-interaction in order to investigate the effect of the fundamental length $q=1/(2\kappa)$ on such diagrams. Thanks to $\kappa$-deformation, we find that the dimensionally regularized forms of the diagrams lead to finite results in the limit of space-time dimension four. The effect of the deformation appears as a displacement of the poles in the complex plane.
- Published
- 2008
- Full Text
- View/download PDF
8. Correlations around an interface
- Author
-
Bessa, A., de Carvalho, C. A. A., and Fraga, E. S.
- Subjects
High Energy Physics - Phenomenology ,Condensed Matter - Statistical Mechanics ,High Energy Physics - Theory - Abstract
We compute one-loop correlation functions for the fluctuations of an interface using a field theory model. We obtain them from Feynman diagrams drawn with a propagator which is the inverse of the Hamiltonian of a Poschl-Teller problem. We derive an expression for the propagator in terms of elementary functions, show that it corresponds to the usual spectral sum, and use it to calculate quantities such as the surface tension and interface profile in two and three spatial dimensions. The three-dimensional quantities are rederived in a simple, unified manner, whereas those in two dimensions extend the existing literature, and are applicable to thin films. In addition, we compute the one-loop self-energy, which may be extracted from experiment, or from Monte Carlo simulations. Our results may be applied in various scenarios, which include fluctuations around topological defects in cosmology, supersymmetric domain walls, Z(N) bubbles in QCD, domain walls in magnetic systems, interfaces separating Bose-Einstein condensates, and interfaces in binary liquid mixtures., Comment: RevTeX, 13 pages, 6 figures
- Published
- 2004
- Full Text
- View/download PDF
9. Alternative dimensional reduction via the density matrix: A test
- Author
-
de Carvalho, C. A. A. and Cavalcanti, R. M.
- Subjects
High Energy Physics - Theory ,Condensed Matter - Statistical Mechanics ,Quantum Physics - Abstract
We derive and analyze the perturbation series for the classical effective action in quantum statistical mechanics, treated as a toy model for the dimensionally reduced effective action in quantum field theory at finite temperature. The first few terms of the series are computed for the harmonic oscillator and the quartic potential., Comment: 7 pages. Published in the Proceedings of the XXIII Brazilian National Meeting on Particles and Fields (October 15-19, Aguas de Lindoia, SP, Brazil), http://www.sbf1.if.usp.br/eventos/enfpc/xxiii/procs/RES191.pdf Eqs.(21) and (23) corrected
- Published
- 2002
10. Improved semiclassical density matrix: taming caustics
- Author
-
de Carvalho, C. A. A., Cavalcanti, R. M., Fraga, E. S., and Joras, S. E.
- Subjects
Quantum Physics ,Condensed Matter - Statistical Mechanics ,High Energy Physics - Phenomenology ,High Energy Physics - Theory - Abstract
We present a simple method to deal with caustics in the semiclassical approximation to the thermal density matrix of a particle moving on the line. For simplicity, only its diagonal elements are considered. The only ingredient we require is the knowledge of the extrema of the Euclidean action. The procedure makes use of complex trajectories, and is applied to the quartic double-well potential., Comment: 20 pages, 7 figures. Revised version, accepted for publication in Phys. Rev. E
- Published
- 2001
- Full Text
- View/download PDF
11. Alternative Dimensional Reduction via the Density Matrix
- Author
-
de Carvalho, C. A. A., Cornwall, John M., and da Silva, A. J.
- Subjects
High Energy Physics - Theory ,Condensed Matter - Statistical Mechanics - Abstract
We give graphical rules, based on earlier work for the functional Schrodinger equation, for constructing the density matrix for scalar and gauge fields at finite temperature T. More useful is a dimensionally-reduced effective action (DREA) constructed from the density matrix by further functional integration over the arguments of the density matrix coupled to a source. The DREA is an effective action in one less dimension which may be computed order by order in perturbation theory or by dressed-loop expansions; it encodes all thermal matrix elements. The DREA is useful because it gives a dimensionally-reduced field theory usable at any T including infinity, where it yields the usual dimensionally-reduced field theory (DRFT). However, it cannot and does not have spurious infinities which sometimes occur in the density matrix or the DRFT; these come from ln T factors at infinite temperature. An example of spurious divergences in the DRFT occurs in d 2+1 $\phi^4$ theory dimensionally reduced to d=2. We show that the rules for the DREA replace these "wrong" divergences in physical parameters by calculable powers of ln T; we also compute the phase transition temperature of this theory at one loop order., Comment: 23 pages, LaTeX, no figures
- Published
- 2001
- Full Text
- View/download PDF
12. Uniform semiclassical approximation in quantum statistical mechanics
- Author
-
de Carvalho, C. A. A., Cavalcanti, R. M., Fraga, E. S., and Joras, S. E.
- Subjects
Condensed Matter - Statistical Mechanics ,High Energy Physics - Theory ,Quantum Physics - Abstract
We present a simple method to deal with caustics in the semiclassical approximation to the partition function of a one-dimensional quantum system. The procedure, which makes use of complex trajectories, is applied to the quartic double-well potential., Comment: 5 pages, 1 figure, Latex. Contribution to the Proceedings of the XXI Brazilian National Meeting on Particles and Fields (Sao Lourenco, October 23-27, 2000)
- Published
- 2000
13. Semiclassical approximation to the partition function of a particle in D dimensions
- Author
-
de Carvalho, C. A. A., Cavalcanti, R. M., Fraga, E. S., and Jorás, S. E.
- Subjects
Quantum Physics ,Condensed Matter - Statistical Mechanics ,High Energy Physics - Phenomenology ,High Energy Physics - Theory - Abstract
We use a path integral formalism to derive the semiclassical series for the partition function of a particle in D dimensions. We analyze in particular the case of attractive central potentials, obtaining explicit expressions for the fluctuation determinant and for the semiclassical two-point function in the special cases of the harmonic and single-well quartic anharmonic oscillators. The specific heat of the latter is compared to precise WKB estimates. We conclude by discussing the possible extension of our results to field theories., Comment: REVTEX,14 pages, 2 figures, final version to appear in Phys. Rev. E
- Published
- 1999
- Full Text
- View/download PDF
14. Semiclassical Series from Path Integrals
- Author
-
de Carvalho, C. A. A. and Cavalcanti, R. M.
- Subjects
Quantum Physics ,Condensed Matter - Statistical Mechanics ,High Energy Physics - Theory - Abstract
We derive the semiclassical series for the partition function in Quantum Statistical Mechanics (QSM) from its path integral representation. Each term of the series is obtained explicitly from the (real) minima of the classical action. The method yields a simple derivation of the exact result for the harmonic oscillator, and an accurate estimate of ground-state energy and specific heat for a single-well quartic anharmonic oscillator. As QSM can be regarded as finite temperature field theory at a point, we make use of Feynman diagrams to illustrate the non-perturbative character of the series: it contains all powers of $\hbar$ and graphs with any number of loops; the usual perturbative series corresponds to a subset of the diagrams of the semiclassical series. We comment on the application of our results to other potentials, to correlation functions and to field theories in higher dimensions., Comment: 18 pages, 4 figures. References updated
- Published
- 1999
- Full Text
- View/download PDF
15. Semiclassical Series at Finite Temperature
- Author
-
de Carvalho, C. A. A., Cavalcanti, R. M., Fraga, E. S., and Joras, S. E.
- Subjects
Quantum Physics ,Condensed Matter - Statistical Mechanics ,High Energy Physics - Theory - Abstract
We derive the semiclassical series for the partition function of a one-dimensional quantum-mechanical system consisting of a particle in a single-well potential. We do this by applying the method of steepest descent to the path-integral representation of the partition function, and we present a systematic procedure to generate the terms of the series using the minima of the Euclidean action as the only input. For the particular case of a quartic anharmonic oscillator, we compute the first two terms of the series, and investigate their high and low temperature limits. We also exhibit the nonperturbative character of the terms, as each corresponds to sums over infinite subsets of perturbative graphs. We illustrate the power of such resummations by extracting from the first term an accurate nonperturbative estimate of the ground-state energy of the system and a curve for the specific heat. We conclude by pointing out possible extensions of our results which include field theories with spherically symmetric classical solutions., Comment: 25 pages + 5 figures
- Published
- 1998
- Full Text
- View/download PDF
16. Perturbative Evidence of Non-Universality in the Quantized Hall Conductivity of a Disordered Relativistic 2D Electron Gas
- Author
-
Bralic, N., de Carvalho, C. A. A., Cavalcanti, R. M., and Donatis, P.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,High Energy Physics - Theory - Abstract
We study a relativistic two-dimensional electron gas in the presence of a uniform external magnetic field and a random static scalar potential. We compute, in first order perturbation theory, the averages of the charge density and of the transverse conductivity for a white-noise potential, and show that, within this treatment, their quantized values are modified by the disorder., Comment: ReVTeX, 7 pages, 1 ps figure. To appear in Mod. Phys. Lett. B. The last reference was corrected
- Published
- 1998
- Full Text
- View/download PDF
17. The weakly disordered 2D electron gas in a magnetic field
- Author
-
Bralic, N., Cavalcanti, R. M., de Carvalho, C. A. A., and Donatis, P.
- Subjects
High Energy Physics - Theory ,Condensed Matter - Abstract
We study a relativistic two-dimensional free electron gas in the presence of a uniform external magnetic field and a random static scalar potential. We compute the expectation values of the charge density and the conductivity tensor, averaged over the random potential in first order perturbation theory. We discuss the effect of a zero vs. finite range correlation length of the random potential., Comment: 9 pages, 4 figures, REVTEX. Last paragraph of section IV removed, references updated
- Published
- 1997
18. Subtleties in Quantum Mechanical Metastability
- Author
-
Cavalcanti, R. M. and de Carvalho, C. A. A.
- Subjects
Quantum Physics ,Condensed Matter ,High Energy Physics - Theory - Abstract
We present a detailed discussion of some features of quantum mechanical metastability. We analyze the nature of decaying (quasistationary) states and the regime of validity of the exponencial law, as well as decays at finite temperature. We resort to very simple systems and elementary techniques to emphasize subtle aspects of the problem., Comment: 8 pages, revtex, a few minor changes, some references added
- Published
- 1996
19. The Role of Fermions in Bubble Nucleation
- Author
-
Barci, D. G., Fraga, E. S., and de Carvalho, C. A. A.
- Subjects
High Energy Physics - Theory ,Condensed Matter ,High Energy Physics - Phenomenology - Abstract
We present a study of the role of fermions in the decay of metastable states of a scalar field via bubble nucleation. We analyze both one and three-dimensional systems by using a gradient expansion for the calculation of the fermionic determinant. The results of the one-dimensional case are compared to the exact results of previous work., Comment: 15 pages, revtex, 9 figures
- Published
- 1996
- Full Text
- View/download PDF
20. Tunnelings as Catastrophes
- Author
-
de Carvalho, C. A. A. and Cavalcanti, R. M.
- Subjects
High Energy Physics - Theory ,Condensed Matter - Abstract
We use path-integrals to derive a general expression for the semiclassical approximation to the partition function of a one-dimensional quantum-mechanical system. Our expression depends solely on ordinary integrals which involve the potential. For high temperatures, the semiclassical expression is dominated by single closed paths. As we lower the temperature, new closed paths appear, including tunneling paths. The transition from single to multiple-path regime corresponds to well-defined catastrophes. Tunneling sets in whenever they occur. (Our formula fully accounts for this feature.), Comment: 5 pages, revtex, 5 figures, uuencoded tar-compressed
- Published
- 1995
21. Thermal Decays in a Hot Fermi Gas
- Author
-
Fraga, E. S. and De Carvalho, C. A. A.
- Subjects
High Energy Physics - Theory ,Condensed Matter ,High Energy Physics - Phenomenology - Abstract
We present a study of the decay of metastable states of a scalar field via thermal activation, in the presence of a finite density of fermions. The process we consider is the nucleation of ``{\it droplets}'' of true vacuum inside the false one. We analyze a one-dimensional system of interacting bosons and fermions, considering the latter at finite temperature and with a given chemical potential. As a consequence of a non-equilibrium formalism previously developed, we obtain time-dependent decay rates., Comment: 18 pages, REVTEX, 9 figures available upon request
- Published
- 1994
- Full Text
- View/download PDF
22. Real Time Analysis of Thermal Activation via Sphaleron Transitions
- Author
-
Boyanovsky, D. and de Carvalho, C. A.
- Subjects
High Energy Physics - Phenomenology ,High Energy Physics - Theory - Abstract
We study the process of thermal activation mediated by sphaleron transitions by analyzing the real-time dynamics of the decay out of equilibrium in a $1+1$ dimensional field theory with a metastable state. The situation considered is that of a rapid supercooling in which the system is trapped in a metastable state at a temperature larger than the mass of the quanta, but smaller than the energy to create a critical droplet. The initial density matrix is evolved in time and the nucleation rate (probability current at the saddle point) is computed. The nucleation rate is {\it time dependent}, vanishing at early times, reaching a maximum at a time $t \approx 1/m$ with $m$ the mass of quanta in the metastable state, and decreasing at long times as a consequence of unitarity. An estimate for the average number of particles of ``true vacuum'' produced as a function of time during the nucleation process is obtained., Comment: 26 pages 6 figures (available upon request), PITT-93-06, LATEX
- Published
- 1993
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.