arXiv subjects

E. C. Marino

Publications and source records attributed to E. C. Marino.

At least 55 records · Page 3Linked to original sources

arXiv2007

Dual Bosonic Thermal Green Function and Fermion Correlators of the Massive Thirring Model at a Finite Temperature

The Euclidian thermal Green function of the two-dimensional (2D) free massless scalar field in coordinate space is written as the real part of a complex analytic function of a variable that conformally maps the infinite strip $-\infty<x<\infty$ ($0<τ<β$) of the $z=x+iτ$ ($τ$: imaginary time) plane into the upper-half-plane. Using this fact and the Cauchy-Riemann conditions, we identify the dual thermal Green function as the imaginary part of that function. Using both the thermal Green function and its dual, we obtain an explicit series expression for the fermionic correlation functions of the massive Thirring model (MTM) at a finite temperature.

hep-th↗

arXiv2007

Magnetic Field Effects on the Superconducting and Quantum Critical Properties of Layered Systems with Dirac Electrons

We study the effects of an external magnetic field on the superconducting properties of a quasi-two-dimensional system of Dirac electrons at an arbitrary temperature. An explicit expression for the superconducting gap is obtained as a function of temperature, magnetic field and coupling parameter ($λ_{\rm R}$). From this, we extract the $B \times λ_{\rm R}$, $T\times λ_{\rm R}$ and $B \times T$ phase diagrams. The last one shows a linear decay of the critical field for small values thereof, which is similar to the behavior observed experimentally in the copper doped dichalcogenide $Cu_xTiSe_2$ and also in intercalated graphite. The second one, presents a coupling dependent critical temperature $T_c$ that resembles the one observed in high-$T_c$ cuprates in the underdoped region and also in $Cu_xTiSe_2$. The first one, exhibits a quantum phase transition connecting a normal and a superconducting phase, occurring at a critical line that corresponds to a magnetic field dependent critical coupling parameter. This should be observed in planar materials containing Dirac electrons, such as $Cu_xTiSe_2$.

cond-mat.supr-con↗

arXiv2006

Quantum global vortex strings in a background field

We consider quantum global vortex string correlation functions, within the Kalb-Ramond framework, in the presence of a background field-strength tensor and investigate the conditions under which this yields a nontrivial contribution to those correlation functions. We show that a background field must be supplemented to the Kalb-Ramond theory, in order to correctly describe the quantum properties of the vortex strings. The explicit form of this background field and the associated quantum vortex string correlation function are derived. The complete expression for the quantum vortex creation operator is explicitly obtained. We discuss the potential applicability of our results in the physics of superfluids and rotating Bose-Einstein condensates.

hep-th↗

arXiv2006

Quantum Criticality and Superconductivity in Quasi-Two-Dimensional Dirac Electronic Systems

We present a theory describing the superconducting (SC) interaction of Dirac electrons in a quasi-two-dimensional system consisting of a stack of N planes. The occurrence of a SC phase is investigated both at T=0 and T\neq 0, in the case of a local interaction, when the theory must be renormalized and also in the situation where a natural physical cutoff is present in the system. In both cases, at T=0, we find a quantum phase transition connecting the normal and SC phases at a certain critical coupling. The phase structure is shown to be robust against quantum fluctuations. The SC gap is determined for T=0 and T\neq 0, both with and without a physical cutoff and the interplay between the gap and the SC order parameter is discussed. Our theory qualitatively reproduces the SC phase transition occurring in the underdoped regime of the high-Tc cuprates. This fact points to the possible relevance of Dirac electrons in the mechanism of high-Tc superconductivity.

cond-mat.supr-con↗

arXiv2005

Exact Asymptotic Behaviour of Fermion Correlation Functions in the Massive Thirring Model

We obtain an exact asymptotic expression for the two-point fermion correlation functions in the massive Thirring model (MTM) and show that, for $β^2=8π$, they reproduce the exactly known corresponding functions of the massless theory, explicitly confirming the irrelevance of the mass term at this point. This result is obtained by using the Coulomb gas representation of the fermionic MTM correlators in the bipolar coordinate system.

hep-th↗

arXiv2005

Quantum corrections to the phase diagram of heavy-fermion superconductors

The competition between magnetism and Kondo effect is the main effect determining the phase diagram of heavy fermion systems. It gives rise to a quantum critical point which governs the low temperature properties of these materials. However, experimental results made it clear that a fundamental ingredient is missing in this description, namely superconductivity. In this paper we make a step forward in the direction of incorporating superconductivity and study the mutual effects of this phase and antiferromagnetism in the phase diagram of heavy fermion metals. Our approach is based on a Ginzburg-Landau theory describing superconductivity and antiferromagnetism in a metal with quantum corrections taken into account through an effective potential. The proximity of an antiferromagnetic instability extends the region of superconductivity in the phase diagram and drives this transition into a first order one. On the other hand superconducting quantum fluctuations near a metallic antiferromagnetic quantum critical point gives rise to a first order transition from a low moment to a high moment state in the antiferromagnet. Antiferromagnetism and superconductivity may both collapse at a quantum bicritical point whose properties we calculate.

cond-mat.str-el↗

arXiv2004

Sine-Gordon/Coulomb Gas Soliton Correlation Functions and an Exact Evaluation of the Kosterlitz-Thouless Critical Exponent

We present an exact derivation for the asymptotic large distance behavior of the spin two-point correlation function in the XY-model. This allows for the exact obtainment of the critical exponent $η=1/4$ at the Kosterlitz-Thouless transition that occurs in this model and in the 2D neutral Coulomb gas and which has been previously obtained by scaling arguments. In order to do that, we use the language of sine-Gordon theory to obtain a Coulomb Gas description of the XY-model spin correlation function, which becomes identified with the soliton correlator of that theory. Using a representation in terms of bipolar coordinates we obtain an exact expression for the asymptotic large distance behavior of the relevant correlator at $β^2=8π$, which corresponds to the Kosterlitz-Thouless transition. The result is obtained by approaching this point from the plasma (high-temperature) phase of the gas. The vortex correlator of the XY-model is also obtained using the same procedure.

cond-mat.stat-mech↗

arXiv2003

Effects of disorder in two-dimensional quantum antiferromagnets

We study the effects of disorder in two-dimensional quantum antiferromagnets on a square lattice, within the nonlinear sigma model approach, by using of a random distribution of spin stiffnesses or zero-temperature-spin-gaps, respectively, in the renormalized classical and quantum disordered phases. The quenched staggered magnetic susceptibility at low temperatures is evaluated in each case. The large distance behavior of the quenched spin correlation function is also obtained in the quantum disordered phase. Disorder is shown to introduce a change from exponential to power-law decay in these functions, indicating that the spin excitations become gapless, in spite of the fact that the system is in a disorder state. A comparison is made with the dual behavior of skyrmion topological excitations in the renormalized classical phase.

cond-mat↗

arXiv2003

Creation operators for 2-branes and duality in BF and Chern-Simons theories in D=5

We explicitly construct the creation operators for the quantum field configurations associated to quantum membranes (2-branes) in BF and generalized Chern-Simons theories in a spacetime of dimension D=5. The creation operators for quantum excitations carrying topological charge are also obtained in the same theories. For the case of D=5 generalized Chern-Simons theory, we show that this operator actually creates an open string with a topological charge at its tip. It is shown that a duality structure exists in general, relating the membrane and topological excitation operators and the corresponding dual algebra is derived. Composite topologically charged membranes are shown to possess generalized statistics that may, in particular, be fermionic. This is the first step for the bosonization procedure in these theories. Potential applications in the full quantization of 2-branes is also briefly discussed.

hep-th↗

arXiv2002

Statistical transmutation of quantum bosonic strings coupled to general four-dimensional Chern-Simons theory

A bosonic string coupled to the generalized Chern-Simons theory in 3+1D acquires a magnetic field along itself, when it is closed, and a topological charge at its extremity, when it is open. We construct the creation operators for the full quantum field states associated to these strings and determine the dual algebra satisfied by them. We show that the creation operator fo the composite state of a quantum closed bosonic string, bearing a magnetic flux, and a topologically charged open bosonic string, possesses generalized statistics. The relation of our results with previous approaches to the problem is also established.

hep-th↗

arXiv2002

A new sequence for topological terms at any spacetime dimensions

We investigate a sequence of quadratic topological terms of the Chern-Simons type in different spacetime dimensions, related by dimensional compactification and sharing the properties of topological mass generation and statistical transmutation. The implications for bosonization in several dimensions are also analyzed.

hep-th↗

arXiv2001

Phase Structure and Universality in Two-Dimensional Disordered Quantum Antiferromagnets

Two-dimensional disordered quantum antiferromagnets are studied by means of a continuum description in which disorder is introduced by a random distribution of couplings (spin stiffnesses) in the ordered phase of the Nonlinear Sigma Model. Quenched soliton (skyrmion) correlation functions are evaluated and used, along with the quenched magnetization, to characterize the phase structure of the system. When magnetic dilution is exponentially suppressed, the introduction of disorder only modifies the subleading terms in the large distance behavior of the soliton correlation functions, yielding the same skyrmion energy as in the pure case. The system is in a ``hard'' disordered Néel phase similar to the ordered antiferromagntic phase occurring in the pure case. Conversely, when magnetic dilution is not exponentially suppressed, the large distance behavior of the correlation functions is drastically changed. The system exists in a new phase in which the energy of quantum skyrmions is equal to zero in spite of the existence of a nonvanishing antiferromagnetic order parameter. This ``soft'' disordered Néel phase is characterized by universality classes which are determined by the behavior of the distribution of random couplings in the small coupling region. The possible relation of this phase with spin glasses is briefly discussed.

cond-mat.str-el↗

arXiv1999

Quantized Skyrmion Fields in 2+1 Dimensions

A fully quantized field theory is developped for the skyrmion topological excitations of the O(3) symmetric CP$^1$-Nonlinear Sigma Model in 2+1D. The method allows for the obtainment of arbitrary correlation functions of quantum skyrmion fields. The two-point function is evaluated in three different situations: a) the pure theory; b) the case when it is coupled to fermions which are otherwise non-interacting and c) the case when an electromagnetic interaction among the fermions is introduced. The quantum skyrmion mass is explicitly obtained in each case from the large distance behavior of the two-point function and the skyrmion statistics is inferred from an analysis of the phase of this function. The ratio between the quantum and classical skyrmion masses is obtained, confirming the tendency, observed in semiclassical calculations, that quantum effects will decrease the skyrmion mass. A brief discussion of asymptotic skyrmion states, based on the short distance behavior of the two-point function, is also presented.

cond-mat↗

arXiv1998

Quantum Skyrmions and the Destruction of Antiferromagnetic Order in High-Temperature Superconductors

A continuous field theory which describes the process of doping in high-T$_c$ superconductors of the YBCO-type is presented. It is shown that the introduction of dopants produces the creation of skyrmion topological excitations on the antiferromagnetic background. The energy of these excitations is evaluated. Destruction of the Néel ground state occurs for a critical value $δ_C$ of the doping parameter for which the skyrmion energy vanishes. We evaluate this at zero temperature, obtaining $δ_C = 0.39 \pm 0.03$ which agrees with the experimental value $δ_C^{exp} = 0.41 \pm 0.02$.

cond-mat↗

arXiv1997

A New Approach for Bosonization of Massive Thirring Model in Three Dimensions

We develop a new approach for bosonization based on the direct comparison of current correlation functions and apply it to the case of the Massive Thirring Model in three dimensions in the weak coupling regime, but with an arbitrary mass. Explicit bosonized forms for the lagrangian and the current are obtained in terms of a vector gauge field. Exact results for the corresponding expressions are also obtained in the case of a free massive fermion. Finally, a comment on the derivation of the current algebra directly from the bosonized expressions is included.

hep-th↗

arXiv1997

Different Approaches for Bosonization in Higher Dimensions

We describe two distinct approaches for bosonization in higher dimensions; one is based on a direct comparison of current correlation functions while the other relies on a Master lagrangean formalism. These are used to bosonise the Massive Thirring Model in three and four dimensions in the weak coupling regime but with an arbitrary fermion mass. In both approaches the explicit bosonised lagrangean and current are derived in terms of gauge fields. The complete equivalence of the two bosonization methods is established. Exact results for the free massive fermion theory are also obtained. Finally, the two-dimensional theory is revisited and the possibility of extending this analysis for arbitrary dimensions is indicated.

hep-th↗

arXiv1996

Duality and an Operator Realization for the Fermi-Bose Transmutation in 3+1 Dimensions

We consider the Maxwell-Higgs system in the broken phase, described in terms of a Kalb-Ramond field interacting with the electromagnetic field through a topological coupling. We then study the creation operators of states which respectively carry a point charge and a closed magnetic string in the electromagnetic language or a point topological charge and a closed Kalb-Ramond charged string in the Kalb-Ramond dual language. Their commutation relation is evaluated, implying they satisfy a dual algebra and their composite possesses generalized statistics. In the local limit where the radius of the string vanishes, only Fermi or Bose statistics are allowed. This provides an explicit operator realization for statistical transmutation in 3+1D.

hep-th↗

arXiv1996

Explicit Bosonization of the Massive Thirring Model in 3+1 Dimensions

We bosonize the Massive Thirring Model in 3+1D for small coupling constant and arbitrary mass. The bosonized action is explicitly obtained both in terms of a Kalb-Ramond tensor field as well as in terms of a dual vector field. An exact bosonization formula for the current is derived. The small and large mass limits of the bosonized theory are examined in both the direct and dual forms. We finally obtain the exact bosonization of the free fermion with an arbitrary mass.

hep-th↗