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C. D. Fosco

Publications and source records attributed to C. D. Fosco.

124 records · Page 7Linked to original sources
arXiv1997

Gauge Invariance and Effective Actions in D=3 at Finite Temperature

For background gauge field configurations reducible to the form Amu = (A3, A(x)) where A3 is a constant, we provide an elementary derivation of the recently obtained result for the exact induced Chern-Simons (CS) effective action in QED3 at finite temperature. The method allows us to extend the result in several useful ways: to obtain the analogous result for the `mixed' CS term in the Dorey-Mavromatos model of parity-conserving planar superconductivity, thereby justifying their argument for flux quantization in the model; to the induced CS term for a tau-dependent flux; and to the term of second order in A(x) (and all orders in A3) in the effective action.

hep-th↗
arXiv1997

On the Field Strength Formulation of Effective QED3

Halpern's field strength's formulation of gauge theories is applied to effective QED_3, namely, a gauge invariant theory for an Abelian gauge field $A_μ$ with non-localities and self-interactions. The resulting description in terms of the pseudovector field $\tilde{F}_μ= ε_{μνλ}\partial_νA_λ$ is applied to different examples.

hep-th↗
arXiv1996

Regularized overlap and the chiral determinant

We study the relationship between the continuum overlap and its corresponding chiral determinant, showing that the former amounts to an unregularised version of the latter. We then construct a regularised continuum overlap, and consider the chiral anomalies that follow therefrom. The relation between these anomalies and the ones derived from the formal (i.e., unregularised) overlap is elucidated.

hep-th↗
arXiv1996

Bosonization of Vector and Axial-Vector Currents in 3+1 Dimensions

The bosonization of a massless fermionic field coupled to both vector and axial-vector external sources is developed, following a path-integral approach. The resulting bosonized theory contains two antisymmetric tensor fields whose actions consist of non-local Kalb-Ramond-like terms plus interactions. Exact bosonization rules that take the axial anomaly for the axial current into account are derived, and an approximated bosonized action is constructed.

hep-th↗
arXiv1996

On the Quantization of the Abelian Chern-Simons Coefficient at Finite Temperature

We show that when the Abelian \CS\ theory coupled to matter fields is quantized in a vacuum with non vanishing magnetic flux (or electric charge), the requirement of gauge invariance at finite temperature leads to the quantization of the \CS\ coefficient and its quantum corrections, in a manner similar to the non-Abelian case.

hep-th↗
arXiv1996

Tunneling between fermionic vacua and the overlap formalism

The probability amplitude for tunneling between the Dirac vacua corresponding to different signs of a parity breaking fermionic mass $M$ in $2+1$ dimensions is studied, making contact with the continuum overlap formulation for chiral determinants. It is shown that the transition probability in the limit when $M \to \infty$ corresponds, via the overlap formalism, to the squared modulus of a chiral determinant in two Euclidean dimensions. The transition probabilities corresponding to two particular examples: fermions on a torus with twisted boundary conditions, and fermions on a disk in the presence of an external constant magnetic field are evaluated.

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arXiv1996

Effective Theory for Parity Conserving $QED_3$

We consider a higher derivative effective theory for an Abelian gauge field in three dimensions, which represents the result of integrating out heavy matter fields interacting with a classical gauge field in a parity-conserving way. We retain terms containing up to two derivatives of $F_{μν}$, but make no assumption about the strength of this field. We then quantize the gauge field, and compute the one-loop effective action for a constant $\fmn$. The result is explicitly evaluated for the case of a constant magnetic field.

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arXiv1996

The SU(2) Non-Linear Sigma-Model in 2+1 Dimensions: Perturbation Theory in a Polynomial Formulation

We construct a perturbation theory for the SU(2) non-linear Sigma-model in 2+1 dimensions using a polynomial, first-order formulation, where the variables are a non-Abelian vector field L_mu (the left SU(2) current), and a non-Abelian pseudovector field $θ_μ$, which imposes the condition F_{mu nu}(L) = 0. The coordinates on the group do not appear in the Feynman rules, but their scattering amplitudes are easily related to those of the currents. We show that all the infinities affecting physical amplitudes at one-loop order can be cured by normal ordering, presenting the calculation of the full propagator as an example of an application.

hep-th↗
arXiv1996

Canonical Structure of the Non-Linear Sigma-Model in a Polynomial Formulation

We study the canonical structure of the $SU(N)$ non-linear Sigma-model in a polynomial, first-order representation. The fundamental variables in this description are a non-Abelian vector field L_mu and a non-Abelian antisymmetric tensor field theta_{mu nu}, which constrains L_{mu} to be a `pure gauge' (F_{mu nu}(L) = 0) field. The second-class constraints that appear as a consequence of the first-order nature of the Lagrangian are solved, and the reduced phase-space variables explicitly found. We also treat the first-class constraints due to the gauge-invariance under transformations of the antisymmetric tensor field, constructing the corresponding most general gauge-invariant functionals, which are used to describe the dynamics of the physical degrees of freedom. We present these results in 1+1, 2+1 and 3+1 dimensions, mentioning some properties of the (d+1)-dimensional case. We show that there is a kind of duality between this description of the non-linear $σ$-model and the massless Yang-Mills theory. This duality is further extended to more general first-class systems.

hep-th↗
arXiv1996

The Ladder Approximation in QED_2

We study the Schwinger-Dyson equation for the fermion self-energy in massless and massive $QED_2$, in the ladder approximation. When the fermion is massless (and the photon massless or massive), we check the reliability of this approximation by comparing its solutions with the exact ones. They agree only when the photon is massless. For a massive fermion and massless photon, we show that there is no consistent solution at all, the infrared divergences introduced by the approximation forbidding even the trivial solution. When both fermion and photon are massive, we find a non-perturbative (extra) fermion mass generation (which survives in the limit when the bare mass of the fermion tends to zero). We argue that, in this case, the ladder approximation will provide reliable results if the bare masses of the fields are large compared with the (dimensionful) coupling constant.

hep-th↗
arXiv1996

The Polynomial Formulation of the U(1) Non-Linear Sigma-Model in 2 Dimensions

We investigate some properties of a first-order polynomial formulation of the U(1) non-linear sigma-model in two Euclidean dimensions. The variables in this description are a 1-form field plus a 0-form Lagrange multiplier field. The usual spin variables are non-local functions of the new fields. As this construction incorporates O(2) invariance ab initio, only O(2)-invariant correlation functions (the only non-vanishing ones in the model) can be constructed. We show that the vortices play a dual role to the spin variables in the partition function. The equivalent Sine-Gordon description is obtained in a natural way, when one integrates out the 1-form field to get an effective partition function for the Lagrange multiplier. We also show how to introduce strings of vortices within this formulation.

hep-th↗
arXiv1995

Continuum and Lattice Overlap for Chiral Fermions on the Torus

The overlap formulation is applied to calculate the chiral determinant on a two-dimensional torus with twisted boundary conditions. We evaluate first the continuum overlap, which is convergent and well-defined, and yields the correct string theory result for both the real and imaginary parts of the effective action. We then show that the lattice version of the overlap gives the continuum overlap results in the limit when the lattice spacing tends to zero, and that the subleading terms in that limit are irrelevant.

hep-th↗
arXiv1995

On bosonization in $3$ dimensions

A recently proposed path-integral bosonization scheme for massive fermions in $3$ dimensions is extended by keeping the full momentum-dependence of the one-loop vacuum polarization tensor. This makes it possible to discuss both the massive and massless fermion cases on an equal footing, and moreover the results it yields for massless fermions are consistent with the ones of another, seemingly different, canonical quantization approach to the problem of bosonization for a massless fermionic field in $3$ dimensions.

hep-th↗
arXiv1995

Determinant of twisted chiral Dirac Operator on the Lattice

Using the overlap formulation, we calculate the fermionic determinant on the lattice for chiral fermions with twisted boundary conditions in two dimensions. When the lattice spacing tends to zero we recover the results of the usual string-theory continuum calculations.

hep-th↗
arXiv1993

Symmetries in a Polynomial Formulation of the Non-Linear Sigma-Model

We study the realisation of global symmetries in a polynomial formulation of the non-linear sigma-model. We show that there are global symmetries whose corresponding Noether currents are the topological currents in the usual formulation. The usual Noether currents associated with the internal symmetry group are reproduced, but part of them become non-local in terms of the dynamical variables of the polynomial formulation.

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