Unstable particles versus resonances in impurity systems, conductance in quantum wires

We compute the DC conductance for a homogeneous sine-Gordon model and an impurity system of Luttinger liquid type by means of the thermodynamic Bethe ansatz and standard potential scattering theory. We demonstrate that unstable particles and resonances in impurity systems lead to a sharp increase of the conductance as a function of the temperature, which is characterized by the Breit-Wigner formula.Comment: 5 pages Latex, 1 figure replaced, version to appear in J. Phys.

Higher particle form factors of branch point twist fields in integrable quantum field theories

In this paper we compute higher particle form factors of branch point twist fields. These fields were first described in the context of massive 1+1-dimensional integrable quantum field theories and their correlation functions are related to the bi-partite entanglement entropy. We find analytic expressions for some form factors and check those expressions for consistency, mainly by evaluating the conformal dimension of the corresponding twist field in the underlying conformal field theory. We find that solutions to the form factor equations are not unique so that various techniques need to be used to identify those corresponding to the branch point twist field we are interested in. The models for which we carry out our study are characterized by staircase patterns of various physical quantities as functions of the energy scale. As the latter is varied, the beta-function associated to these theories comes close to vanishing at several points between the deep infrared and deep ultraviolet regimes. In other words, renormalisation group flows approach the vicinity of various critical points before ultimately reaching the ultraviolet fixed point. This feature provides an optimal way of checking the consistency of higher particle form factor solutions, as the changes on the conformal dimension of the twist field at various energy scales can only be accounted for by considering higher particle form factor contributions to the expansion of certain correlation functions.Comment: 25 pages, 4 figures; v2 contains small correction

Entanglement Content of Quantum Particle Excitations II. Disconnected Regions and Logarithmic Negativity

In this paper we study the increment of the entanglement entropy and of the (replica) logarithmic negativity in a zero-density excited state of a free massive bosonic theory, compared to the ground state. This extends the work of two previous publications by the same authors. We consider the case of two disconnected regions and find that the change in the entanglement entropy depends only on the combined size of the regions and is independent of their connectivity. We subsequently generalize this result to any number of disconnected regions. For the replica negativity we find that its increment is a polynomial with integer coefficients depending only on the sizes of the two regions. The logarithmic negativity turns out to have a more complicated functional structure than its replica version, typically involving roots of polynomials on the sizes of the regions. We obtain our results by two methods already employed in previous work: from a qubit picture and by computing four-point functions of branch point twist fields in finite volume. We test our results against numerical simulations on a harmonic chain and find excellent agreement

Applications of quantum integrable systems

We present two applications of quantum integrable systems. First, we predict that it is possible to generate high harmonics from solid state devices by demostrating that the emission spectrum for a minimally coupled laser field of frequency $\omega$ to an impurity system of a quantum wire, contains multiples of the incoming frequency. Second, evaluating expressions for the conductance in the high temperature regime we show that the caracteristic filling fractions of the Jain sequence, which occur in the fractional quantum Hall effect, can be obtained from quantum wires which are described by minimal affine Toda field theories.Comment: 25 pages of LaTex, 4 figures, based on talk at the 6-th international workshop on conformal field theories and integrable models, (Chernogolovka, September 2002

Entropy inequalities from reflection positivity

We investigate the question of whether the entropy and the Renyi entropies of the vacuum state reduced to a region of the space can be represented in terms of correlators in quantum field theory. In this case, the positivity relations for the correlators are mapped into inequalities for the entropies. We write them using a real time version of reflection positivity, which can be generalized to general quantum systems. Using this generalization we can prove an infinite sequence of inequalities which are obeyed by the Renyi entropies of integer index. There is one independent inequality involving any number of different subsystems. In quantum field theory the inequalities acquire a simple geometrical form and are consistent with the integer index Renyi entropies being given by vacuum expectation values of twisting operators in the Euclidean formulation. Several possible generalizations and specific examples are analyzed.Comment: Significantly enlarged and corrected version. Counterexamples found for the most general form of the inequalities. V3: minor change

Breathers in the elliptic sine-Gordon model

We provide new expressions for the scattering amplitudes in the soliton-antisoliton sector of the elliptic sine-Gordon model in terms of cosets of the affine Weyl group corresponding to infinite products of q-deformed gamma functions. When relaxing the usual restriction on the coupling constants, the model contains additional bound states which admit an interpretation as breathers. These breather bound states are unavoidably accompanied by Tachyons. We compute the complete S-matrix describing the scattering of the breathers amonst themselves and with the soliton-antisoliton sector. We carry out various reductions of the model, one of them leading to a new type of theory, namely an elliptic version of the minimal D(n+1)-affine Toda field theory.Comment: 20 pages, Latex, one eps-figur

Constructing Infinite Particle Spectra

We propose a general construction principle which allows to include an infinite number of resonance states into a scattering matrix of hyperbolic type. As a concrete realization of this mechanism we provide new S-matrices generalizing a class of hyperbolic ones, which are related to a pair of simple Lie algebras, to the elliptic case. For specific choices of the algebras we propose elliptic generalizations of affine Toda field theories and the homogeneous sine-Gordon models. For the generalization of the sinh-Gordon model we compute explicitly renormalization group scaling functions by means of the c-theorem and the thermodynamic Bethe ansatz. In particular we identify the Virasoro central charges of the corresponding ultraviolet conformal field theories.Comment: 7 pages Latex, 7 figures (typo in figure 3 corrected

Entanglement Oscillations near a Quantum Critical Point

We study the dynamics of entanglement in the scaling limit of the Ising spin chain in the presence of both a longitudinal and a transverse field. We present analytical results for the quench of the longitudinal field in the critical transverse field which go beyond current lattice integrability techniques. We test these results against a numerical simulation on the corresponding lattice model finding extremely good agreement. We show that the presence of bound states in the spectrum of the field theory leads to oscillations in the entanglement entropy and suppresses its linear growth on the time scales accessible to numerical simulations. For small quenches, we exactly determine these oscillatory contributions and demonstrate that their presence follows from symmetry arguments. For the quench of the transverse field at zero longitudinal field, we prove that the Rényi entropies are exactly proportional to the logarithm of the exponential of a time-dependent function, whose leading large-time behavior is linear, hence, entanglement grows linearly. We conclude that, in the scaling limit, linear growth and oscillations in the entanglement entropies can not be simply seen as consequences of integrability and its breaking, respectively

Form factors of boundary fields for A(2)-affine Toda field theory

In this paper we carry out the boundary form factor program for the A(2)-affine Toda field theory at the self-dual point. The latter is an integrable model consisting of a pair of particles which are conjugated to each other and possessing two bound states resulting from the scattering processes 1 +1 -> 2 and 2+2-> 1. We obtain solutions up to four particle form factors for two families of fields which can be identified with spinless and spin-1 fields of the bulk theory. Previously known as well as new bulk form factor solutions are obtained as a particular limit of ours. Minimal solutions of the boundary form factor equations for all A(n)-affine Toda field theories are given, which will serve as starting point for a generalisation of our results to higher rank algebras.Comment: 24 pages LaTeX, 1 figur

Estudio de fatiga térmica de cermets base hierro

Ponencia presentada en: XI Congreso Nacional de Materiales Compuestos, celebrado los días 6, 7 y 8 de julio de 2015, en Móstoles (España).En el presente trabajo se analiza el comportamiento a fatiga térmica de materiales compuestos de matriz férrea y refuerzo de TiCN desde dos puntos de vista: la influencia de la temperatura máxima alcanzada durante la fatiga térmica y la influencia del número de ciclos de calentamiento y enfriamiento. Además, se compara el comportamiento de estos materiales con el de un acero de herramientas de uso convencional. Este estudio del comportamiento frente a cambios cíclicos de temperatura para ambos materiales se realiza en base a su resistencia a la oxidación y se compara con la oxidación estática que se produce a temperatura elevada constante. Para ello las probetas se han sometido a diferentes ciclos de fatiga térmica, alcanzando temperaturas máximas de 1000 ºC durante un máximo de 100 ciclos; posteriormente se ha caracterizado tanto su superficie como su sección transversal utilizando diferentes técnicas: medida de cambio de masa, DRX, SEM, EDX y microdureza.Los autores agradecen la financiación recibida para la realización de este trabajo al MINECO (proyecto MAT2012-38650-C02-01) y a la Comunidad de Madrid por el programa MULTIMAT-CHALLENGE, ref. S2013/MIT-2862Publicad