Navegando por Autor "Brandt, Fernando Tadeu Caldeira"
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Artigo Pressure of massless hot scalar theory in the boundary effective theory framework(American Physical Society, 2011-04-22) Moreira, André Bessa; Brandt, Fernando Tadeu Caldeira; Carvalho Filho, Carlos Alberto Aragão de; Fraga, Eduardo SouzaWe use the boundary effective theory approach to thermal field theory in order to calculate the pressure of a system of massless scalar fields with quartic interaction. The method naturally separates the infrared physics, and is essentially nonperturbative. To lowest order, the main ingredient is the solution of the free Euler-Lagrange equation with nontrivial (time) boundary conditions. We derive a resummed pressure, which is in good agreement with recent calculations found in the literature, following a very direct and compact procedureArtigo Quantum statistical correlations in thermal field theories: boundary effective theory(American Physical Society, 2010-09-08) Moreira, André Bessa; Brandt, Fernando Tadeu Caldeira; Carvalho Filho, Carlos Alberto Aragão de; Fraga, Eduardo SouzaWe 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 ϕc, 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 Schrödinger 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 ϕc, 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