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Filipe Freire

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Papers by Filipe Freire

Remarks on the non-local gauge invariant extensions of $A^2$

In this letter, we illustrate general properties of gauge invariant extensions of the local funct... more In this letter, we illustrate general properties of gauge invariant extensions of the local functional O = 1 2 ∫ d4xA2. We show that these extensions have long range non localities which can only be “renormalised” with reference to a specific gauge. Therefore, there is no gauge independent way of claiming the renormalisability of these extensions. In particular, they are not renormalisable in the modern sense. As a consequence, if the renormalisability of an extension of O is formally redefined in any gauge by going back to the gauge where the functional takes a local form, the renormalisation procedure is tied to this gauge, and renormalisability is no longer a gauge independent property.

Phase diagram of superconductors from nonperturbative flow equations

Physical Review B, 1996

The universal behavior of superconductors near the phase transition is described by the three-dim... more The universal behavior of superconductors near the phase transition is described by the three-dimensional field theory of scalar quantum electrodynamics. We approximately solve the model with the help of nonperturbative flow equations. A first-or second-order phase transition is found depending on the relative strength of the scalar versus the gauge coupling. The region of a second-order phase transition is governed by a fixed point of the flow equations with associated critical exponents. We also give an approximate description of the tricritical behavior and briefly discuss the crossover relevant for the onset of scaling near the critical temperature. Final confirmation of a second-order transition for strong type-II superconductors requires further analysis with extended truncations of the flow equations.

On the renormalisability of gauge invariant extensions of the squared gauge potential

We show that gauge invariant extensions of the local functional $\cO = \frac12\int d^4x A^2$ have... more We show that gauge invariant extensions of the local functional $\cO = \frac12\int d^4x A^2$ have long range non localities which can only be ``renormalised'' with reference to a specific gauge. Consequently, there is no gauge independent way of claiming the perturbative renormalisability of these extensions. In particular, they are not renormalisable in the modern sense of Weinberg and Gomis. Critically, our study does not support the view that ghost fields play an indispensable role in the extension of a local operator into a non-local one as claimed recently in the literature.

We study the symmetry breaking pattern of a model with an O(4) scalar field sector, with both cha... more We study the symmetry breaking pattern of a model with an O(4) scalar field sector, with both charged and neutral fields, interacting with a photon bath. Here it is shown that a selective con-densation of the neutral fields, that are not directly coupled to photons, can be achieved in the presence of a minimal “external ” dissipation, i.e. not related to interactions with a bath. Pre-liminary results from simulations illustrating defect formation are also discussed. This should be relevant in the early universe or in heavy-ion collisions where dissipation occurs due to expansion. 29th Johns Hopkins Workshop on current problems in particle theory: strong matter in the heavens

The role of dissipation in biasing the vacuum selection in quantum field theory at finite temperature

We study the symmetry breaking pattern of an O(4) symmetric model of scalar fields, with both cha... more We study the symmetry breaking pattern of an O(4) symmetric model of scalar fields, with both charged and neutral fields, interacting with a photon bath. Nagasawa and Brandenberger argued that in favourable circumstances the vacuum manifold would be reduced from S^3 to S^1. Here it is shown that a selective condensation of the neutral fields, that are not directly coupled to photons, can be achieved in the presence of a minimal ``external'' dissipation, i.e. not related to interactions with a bath. This should be relevant in the early universe or in heavy-ion collisions where dissipation occurs due to expansion.

Charge cross-over at the U(1)-Higgs phase transition

The type-I region of phase transitions at finite temperature of the U(1)-Higgs theory in 3+1 dime... more The type-I region of phase transitions at finite temperature of the U(1)-Higgs theory in 3+1 dimensions is investigated in detail using a Wilsonian renormalisation group. We consider in particular the quantitative effects induced through the cross-over of the scale-dependent Abelian charge from the Gaussian to a non-trivial Abelian fixed point. As a result, the strength of the first-order phase transition is weakened. Analytical solutions to approximate flow equations are obtained, and all characteristics of the phase transition are discussed and compared to the results obtained from perturbation theory. In addition, we present a detailed quantitative study regarding the dependence of the physical observables on the coarse-graining scheme. This results in error-bars for the regularisation scheme (RS) dependence. We find quantitative evidence for an intimate link between the RS dependence and truncations of flow equations.

Dissipation and vacuum selection

Proceedings of 29th Johns Hopkins Workshop on current problems in particle theory: strong matter in the heavens — PoS(JHW2005)

We study the symmetry breaking pattern of a model with an O(4) scalar field sector, with both cha... more We study the symmetry breaking pattern of a model with an O(4) scalar field sector, with both charged and neutral fields, interacting with a photon bath. Here it is shown that a selective condensation of the neutral fields, that are not directly coupled to photons, can be achieved in the presence of a minimal "external" dissipation, i.e. not related to interactions with a bath. Preliminary results from simulations illustrating defect formation are also discussed. This should be relevant in the early universe or in heavy-ion collisions where dissipation occurs due to expansion. 29th Johns Hopkins Workshop on current problems in particle theory: strong matter in the heavens 1-3 August Budapest * Speaker.

Gauge symmetry breaking in compact multiply connected manifolds

Physics Letters B

Dimensional crossover and finite-size scaling belowT c

J Statist Phys, 1994

Using the formalism developed in earlier work, dimensional crossover on ad-dimensional layered Is... more Using the formalism developed in earlier work, dimensional crossover on ad-dimensional layered Ising-type system satisfying periodic boundary conditions and of sizeL is considered belowTc(L), Tc(L) being the critical temperature of the finite-size system. Effective critical exponents δeff and βeff are shown explicitly to crossover between theird- and (d−1)-dimensional values for ξL→∞ in the limitsL/ξL→∞ andL/ξL→0, respectively, ξL, being the correlation

Can Out-Of Plasma Effects Create Embedded Strings?

ABSTRACT We show that out-of-equilibrium plasma effects provide the conditions for the formation ... more ABSTRACT We show that out-of-equilibrium plasma effects provide the conditions for the formation of embedded vortex-strings. The necessary conditions are an efficient dissipation mechanism for the field modes forming the string and a not too large scalar self-coupling right below the transition scale. We discuss the cosmological implications at the chiral, electroweak and GUT symmetry breaking scales.

Can Out-Of-Equilibrium Plasma Effects Create Embedded Strings?

PASCOS 2004 Part I: Particles, Strings and Cosmology - Proceedings of the 10th International Symposium, Part II: Themes in Unification - The Pran Nath Festschrift - Proceedings of the 10th International Symposium, 2005

ABSTRACT We show that out-of-equilibrium plasma effects provide the conditions for the formation ... more ABSTRACT We show that out-of-equilibrium plasma effects provide the conditions for the formation of embedded vortex-strings. The necessary conditions are an efficient dissipation mechanism for the field modes forming the string and a not too large scalar self-coupling right below the transition scale. We discuss the cosmological implications at the chiral, electroweak and GUT symmetry breaking scales.

Specific heat of a ferromagnetic film

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1996

We analyze the specific heat for the O(N) vector model on a d-dimensional film geometry of thickn... more We analyze the specific heat for the O(N) vector model on a d-dimensional film geometry of thickness L using "environmentally friendly" renormalization. We consider periodic, Dirichlet and antiperiodic boundary conditions, deriving expressions for the specific heat and an effective specific heat exponent, α ef f .

SU(2) Abelian Projected Action for Renormalisation Group Flows

Confinement, Topology, and Other Non-Perturbative Aspects of QCD, 2002

The dual Meissner effect scenario of confinement is analysed using exact renormalisation group (E... more The dual Meissner effect scenario of confinement is analysed using exact renormalisation group (ERG) equations. In particular, the low energy regime of SU (2) Yang-Mills (YM) is studied in a maximal Abelian gauge (MAG). It is shown that under general conditions the effective action derived when integrated using ERG methods contains the relevant degrees of freedom for confinement. In addition, the physics in the confining regime is dual to that of the broken phase of an Abelian Higgs model.

Electroweak Physics and the Early Universe

NATO ASI Series, 1994

The original calculation of 'spontaneous' baryogenesis overlooked the role played by transport of... more The original calculation of 'spontaneous' baryogenesis overlooked the role played by transport of particles onto the bubbles wall. For typical 'adiabatic' wall thicknesses and velocities one can model the problem in a fluid approximation and the mechanism is best understood as another limit of 'charge transport' baryogenesis, and can produce a similar non-local effect in front of the wall.

Abelian projected SU(2) Yang–Mills action for renormalisation group flows

Physics Letters B, 2002

The dual Meissner effect scenario of confinement is discussed by studying the low energy regime o... more The dual Meissner effect scenario of confinement is discussed by studying the low energy regime of SU (2) Yang-Mills in a maximal Abelian gauge. The Abelian projected effective action is computed perturbatively. This serves as an input for a study of the non-perturbative regime, which is undertaken using exact renormalisation group methods. It is argued that the effective action derived here contains the relevant degrees of freedom for confinement if ultraviolet irrelevant vertices are retained.

Consistent non-abelian anomalies via the Fujikawa method

Physics Letters B, 1989

Abelian Ward identity from the background field dependence of the effective action

Physics Letters B, 1996

The dependence of the effective action for gauge theories on the background field obeys an exact ... more The dependence of the effective action for gauge theories on the background field obeys an exact identity. We argue that for Abelian theories the Ward identity follows from the more general background field identity. This observation is particularly relevant for the anomalous Ward identity valid for gauge theories with an effective infrared cutoff as used for flow equations.

Gauge invariance and background field formalism in the exact renormalisation group

Physics Letters B, 2000

We discuss gauge symmetry and Ward-Takahashi identities for Wilsonian flows in pure Yang-Mills th... more We discuss gauge symmetry and Ward-Takahashi identities for Wilsonian flows in pure Yang-Mills theories. The background field formalism is used for the construction of a gauge invariant effective action. The symmetries of the effective action under gauge transformations for both the gauge field and the auxiliary background field are separately evaluated. We examine how the symmetry properties of the full theory are restored in the limit where the cutoff is removed.

Renormalisability of gauge invariant extensions of the squared gauge potential

Physics Letters B, 2004

We show that gauge invariant extensions of the local functional O = 1 2 d 4 xA 2 have long range ... more We show that gauge invariant extensions of the local functional O = 1 2 d 4 xA 2 have long range non localities which can only be "renormalised" with reference to a specific gauge. Consequently, there is no gauge independent way of claiming the perturbative renormalisability of these extensions. In particular, they are not renormalisable in the modern sense of Weinberg and Gomis. Critically, our study does not support the view that ghost fields play an indispensable role in the extension of a local operator into a non-local one as claimed recently in the literature.

Unphysical nature of the SL(2,R) symmetry and its associated condensates in Yang-Mills theories

Physical Review D, 2004

BRST cohomology methods are used to explain the origin of the SL(2, R) symmetry in Yang-Mills the... more BRST cohomology methods are used to explain the origin of the SL(2, R) symmetry in Yang-Mills theories. Clear evidence is provided for the unphysical nature of this symmetry. This is obtained from the analysis of a local functional of mass dimension two and constitutes a no-go statement for giving a physical meaning to condensates associated with the symmetry breaking of SL(2, R).

Remarks on the non-local gauge invariant extensions of $A^2$

In this letter, we illustrate general properties of gauge invariant extensions of the local funct... more In this letter, we illustrate general properties of gauge invariant extensions of the local functional O = 1 2 ∫ d4xA2. We show that these extensions have long range non localities which can only be “renormalised” with reference to a specific gauge. Therefore, there is no gauge independent way of claiming the renormalisability of these extensions. In particular, they are not renormalisable in the modern sense. As a consequence, if the renormalisability of an extension of O is formally redefined in any gauge by going back to the gauge where the functional takes a local form, the renormalisation procedure is tied to this gauge, and renormalisability is no longer a gauge independent property.

Phase diagram of superconductors from nonperturbative flow equations

Physical Review B, 1996

The universal behavior of superconductors near the phase transition is described by the three-dim... more The universal behavior of superconductors near the phase transition is described by the three-dimensional field theory of scalar quantum electrodynamics. We approximately solve the model with the help of nonperturbative flow equations. A first-or second-order phase transition is found depending on the relative strength of the scalar versus the gauge coupling. The region of a second-order phase transition is governed by a fixed point of the flow equations with associated critical exponents. We also give an approximate description of the tricritical behavior and briefly discuss the crossover relevant for the onset of scaling near the critical temperature. Final confirmation of a second-order transition for strong type-II superconductors requires further analysis with extended truncations of the flow equations.

On the renormalisability of gauge invariant extensions of the squared gauge potential

We show that gauge invariant extensions of the local functional $\cO = \frac12\int d^4x A^2$ have... more We show that gauge invariant extensions of the local functional $\cO = \frac12\int d^4x A^2$ have long range non localities which can only be ``renormalised'' with reference to a specific gauge. Consequently, there is no gauge independent way of claiming the perturbative renormalisability of these extensions. In particular, they are not renormalisable in the modern sense of Weinberg and Gomis. Critically, our study does not support the view that ghost fields play an indispensable role in the extension of a local operator into a non-local one as claimed recently in the literature.

We study the symmetry breaking pattern of a model with an O(4) scalar field sector, with both cha... more We study the symmetry breaking pattern of a model with an O(4) scalar field sector, with both charged and neutral fields, interacting with a photon bath. Here it is shown that a selective con-densation of the neutral fields, that are not directly coupled to photons, can be achieved in the presence of a minimal “external ” dissipation, i.e. not related to interactions with a bath. Pre-liminary results from simulations illustrating defect formation are also discussed. This should be relevant in the early universe or in heavy-ion collisions where dissipation occurs due to expansion. 29th Johns Hopkins Workshop on current problems in particle theory: strong matter in the heavens

The role of dissipation in biasing the vacuum selection in quantum field theory at finite temperature

We study the symmetry breaking pattern of an O(4) symmetric model of scalar fields, with both cha... more We study the symmetry breaking pattern of an O(4) symmetric model of scalar fields, with both charged and neutral fields, interacting with a photon bath. Nagasawa and Brandenberger argued that in favourable circumstances the vacuum manifold would be reduced from S^3 to S^1. Here it is shown that a selective condensation of the neutral fields, that are not directly coupled to photons, can be achieved in the presence of a minimal ``external'' dissipation, i.e. not related to interactions with a bath. This should be relevant in the early universe or in heavy-ion collisions where dissipation occurs due to expansion.

Charge cross-over at the U(1)-Higgs phase transition

The type-I region of phase transitions at finite temperature of the U(1)-Higgs theory in 3+1 dime... more The type-I region of phase transitions at finite temperature of the U(1)-Higgs theory in 3+1 dimensions is investigated in detail using a Wilsonian renormalisation group. We consider in particular the quantitative effects induced through the cross-over of the scale-dependent Abelian charge from the Gaussian to a non-trivial Abelian fixed point. As a result, the strength of the first-order phase transition is weakened. Analytical solutions to approximate flow equations are obtained, and all characteristics of the phase transition are discussed and compared to the results obtained from perturbation theory. In addition, we present a detailed quantitative study regarding the dependence of the physical observables on the coarse-graining scheme. This results in error-bars for the regularisation scheme (RS) dependence. We find quantitative evidence for an intimate link between the RS dependence and truncations of flow equations.

Dissipation and vacuum selection

Proceedings of 29th Johns Hopkins Workshop on current problems in particle theory: strong matter in the heavens — PoS(JHW2005)

We study the symmetry breaking pattern of a model with an O(4) scalar field sector, with both cha... more We study the symmetry breaking pattern of a model with an O(4) scalar field sector, with both charged and neutral fields, interacting with a photon bath. Here it is shown that a selective condensation of the neutral fields, that are not directly coupled to photons, can be achieved in the presence of a minimal "external" dissipation, i.e. not related to interactions with a bath. Preliminary results from simulations illustrating defect formation are also discussed. This should be relevant in the early universe or in heavy-ion collisions where dissipation occurs due to expansion. 29th Johns Hopkins Workshop on current problems in particle theory: strong matter in the heavens 1-3 August Budapest * Speaker.

Gauge symmetry breaking in compact multiply connected manifolds

Physics Letters B

Dimensional crossover and finite-size scaling belowT c

J Statist Phys, 1994

Using the formalism developed in earlier work, dimensional crossover on ad-dimensional layered Is... more Using the formalism developed in earlier work, dimensional crossover on ad-dimensional layered Ising-type system satisfying periodic boundary conditions and of sizeL is considered belowTc(L), Tc(L) being the critical temperature of the finite-size system. Effective critical exponents δeff and βeff are shown explicitly to crossover between theird- and (d−1)-dimensional values for ξL→∞ in the limitsL/ξL→∞ andL/ξL→0, respectively, ξL, being the correlation

Can Out-Of Plasma Effects Create Embedded Strings?

ABSTRACT We show that out-of-equilibrium plasma effects provide the conditions for the formation ... more ABSTRACT We show that out-of-equilibrium plasma effects provide the conditions for the formation of embedded vortex-strings. The necessary conditions are an efficient dissipation mechanism for the field modes forming the string and a not too large scalar self-coupling right below the transition scale. We discuss the cosmological implications at the chiral, electroweak and GUT symmetry breaking scales.

Can Out-Of-Equilibrium Plasma Effects Create Embedded Strings?

PASCOS 2004 Part I: Particles, Strings and Cosmology - Proceedings of the 10th International Symposium, Part II: Themes in Unification - The Pran Nath Festschrift - Proceedings of the 10th International Symposium, 2005

ABSTRACT We show that out-of-equilibrium plasma effects provide the conditions for the formation ... more ABSTRACT We show that out-of-equilibrium plasma effects provide the conditions for the formation of embedded vortex-strings. The necessary conditions are an efficient dissipation mechanism for the field modes forming the string and a not too large scalar self-coupling right below the transition scale. We discuss the cosmological implications at the chiral, electroweak and GUT symmetry breaking scales.

Specific heat of a ferromagnetic film

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1996

We analyze the specific heat for the O(N) vector model on a d-dimensional film geometry of thickn... more We analyze the specific heat for the O(N) vector model on a d-dimensional film geometry of thickness L using "environmentally friendly" renormalization. We consider periodic, Dirichlet and antiperiodic boundary conditions, deriving expressions for the specific heat and an effective specific heat exponent, α ef f .

SU(2) Abelian Projected Action for Renormalisation Group Flows

Confinement, Topology, and Other Non-Perturbative Aspects of QCD, 2002

The dual Meissner effect scenario of confinement is analysed using exact renormalisation group (E... more The dual Meissner effect scenario of confinement is analysed using exact renormalisation group (ERG) equations. In particular, the low energy regime of SU (2) Yang-Mills (YM) is studied in a maximal Abelian gauge (MAG). It is shown that under general conditions the effective action derived when integrated using ERG methods contains the relevant degrees of freedom for confinement. In addition, the physics in the confining regime is dual to that of the broken phase of an Abelian Higgs model.

Electroweak Physics and the Early Universe

NATO ASI Series, 1994

The original calculation of 'spontaneous' baryogenesis overlooked the role played by transport of... more The original calculation of 'spontaneous' baryogenesis overlooked the role played by transport of particles onto the bubbles wall. For typical 'adiabatic' wall thicknesses and velocities one can model the problem in a fluid approximation and the mechanism is best understood as another limit of 'charge transport' baryogenesis, and can produce a similar non-local effect in front of the wall.

Abelian projected SU(2) Yang–Mills action for renormalisation group flows

Physics Letters B, 2002

The dual Meissner effect scenario of confinement is discussed by studying the low energy regime o... more The dual Meissner effect scenario of confinement is discussed by studying the low energy regime of SU (2) Yang-Mills in a maximal Abelian gauge. The Abelian projected effective action is computed perturbatively. This serves as an input for a study of the non-perturbative regime, which is undertaken using exact renormalisation group methods. It is argued that the effective action derived here contains the relevant degrees of freedom for confinement if ultraviolet irrelevant vertices are retained.

Consistent non-abelian anomalies via the Fujikawa method

Physics Letters B, 1989

Abelian Ward identity from the background field dependence of the effective action

Physics Letters B, 1996

The dependence of the effective action for gauge theories on the background field obeys an exact ... more The dependence of the effective action for gauge theories on the background field obeys an exact identity. We argue that for Abelian theories the Ward identity follows from the more general background field identity. This observation is particularly relevant for the anomalous Ward identity valid for gauge theories with an effective infrared cutoff as used for flow equations.

Gauge invariance and background field formalism in the exact renormalisation group

Physics Letters B, 2000

We discuss gauge symmetry and Ward-Takahashi identities for Wilsonian flows in pure Yang-Mills th... more We discuss gauge symmetry and Ward-Takahashi identities for Wilsonian flows in pure Yang-Mills theories. The background field formalism is used for the construction of a gauge invariant effective action. The symmetries of the effective action under gauge transformations for both the gauge field and the auxiliary background field are separately evaluated. We examine how the symmetry properties of the full theory are restored in the limit where the cutoff is removed.

Renormalisability of gauge invariant extensions of the squared gauge potential

Physics Letters B, 2004

We show that gauge invariant extensions of the local functional O = 1 2 d 4 xA 2 have long range ... more We show that gauge invariant extensions of the local functional O = 1 2 d 4 xA 2 have long range non localities which can only be "renormalised" with reference to a specific gauge. Consequently, there is no gauge independent way of claiming the perturbative renormalisability of these extensions. In particular, they are not renormalisable in the modern sense of Weinberg and Gomis. Critically, our study does not support the view that ghost fields play an indispensable role in the extension of a local operator into a non-local one as claimed recently in the literature.

Unphysical nature of the SL(2,R) symmetry and its associated condensates in Yang-Mills theories

Physical Review D, 2004

BRST cohomology methods are used to explain the origin of the SL(2, R) symmetry in Yang-Mills the... more BRST cohomology methods are used to explain the origin of the SL(2, R) symmetry in Yang-Mills theories. Clear evidence is provided for the unphysical nature of this symmetry. This is obtained from the analysis of a local functional of mass dimension two and constitutes a no-go statement for giving a physical meaning to condensates associated with the symmetry breaking of SL(2, R).