Entanglement spectrum of random-singlet quantum critical points

The entanglement spectrum, i.e., the full distribution of Schmidt eigenvalues of the reduced density matrix, contains more information than the conventional entanglement entropy and has been studied recently in several many-particle systems. We compute the disorder-averaged entanglement spectrum, in the form of the disorder-averaged moments of the reduced density matrix, for a contiguous block of many spins at the random-singlet quantum critical point in one dimension. The result compares well in the scaling limit with numerical studies on the random XX model and is also expected to describe the (interacting) random Heisenberg model. Our numerical studies on the XX case reveal that the dependence of the entanglement entropy and spectrum on the geometry of the Hilbert space partition is quite different than for conformally invariant critical points.Comment: 11 pages, 10 figure

Corrections to scaling in entanglement entropy from boundary perturbations

We investigate the corrections to scaling of the Renyi entropies of a region of size l at the end of a semi-infinite one-dimensional system described by a conformal field theory when the corrections come from irrelevant boundary operators. The corrections from irrelevant bulk operators with scaling dimension x have been studied by Cardy and Calabrese (2010), and they found not only the expected corrections of the form l^(4-2x) but also unusual corrections that could not have been anticipated by finite-size scaling arguments alone. However, for the case of perturbations from irrelevant boundary operators we find that the only corrections that can occur to leading order are of the form l^(2-2x_b) for boundary operators with scaling dimension x_b < 3/2, and l^(-1) when x_b > 3/2. When x_b=3/2 they are of the form l^(-1)log(l). A marginally irrelevant boundary perturbation will give leading corrections going as log(l)^(-3). No unusual corrections occur when perturbing with a boundary operator.Comment: 8 pages. Minor improvements and updated references. Published versio

Quantum Quench in the Transverse Field Ising chain I: Time evolution of order parameter correlators

We consider the time evolution of order parameter correlation functions after a sudden quantum quench of the magnetic field in the transverse field Ising chain. Using two novel methods based on determinants and form factor sums respectively, we derive analytic expressions for the asymptotic behaviour of one and two point correlators. We discuss quenches within the ordered and disordered phases as well as quenches between the phases and to the quantum critical point. We give detailed account of both methods.Comment: 65 pages, 21 figures, some typos correcte

Universal parity effects in the entanglement entropy of XX chains with open boundary conditions

We consider the Renyi entanglement entropies in the one-dimensional XX spin-chains with open boundary conditions in the presence of a magnetic field. In the case of a semi-infinite system and a block starting from the boundary, we derive rigorously the asymptotic behavior for large block sizes on the basis of a recent mathematical theorem for the determinant of Toeplitz plus Hankel matrices. We conjecture a generalized Fisher-Hartwig form for the corrections to the asymptotic behavior of this determinant that allows the exact characterization of the corrections to the scaling at order o(1/l) for any n. By combining these results with conformal field theory arguments, we derive exact expressions also in finite chains with open boundary conditions and in the case when the block is detached from the boundary.Comment: 24 pages, 9 figure

Compact RF accelerators for nuclear waste characterization

Part of the management of radioactive waste produced by industrial, research or medical processes passes through their characterization with nuclear techniques using neutron sources (typically a D-T tube produces 106 n/pulse, 10 us 100 Hz). On the basis of what has been developed by INFN for other applications (IFMIF, ESS, BNCT...) it is possible to build a much more intense neutron source (109 n/pulse), based on a relatively compact 5 MeV RF linear accelerator and a thick beryllium target, exploiting 9Be(p,n)9B. This talk will recall what was discussed between SOGIN and INFN in recent years (MUNES project) in the light of the most recent results obtained by INFN in the field of linear accelerators

Epidermal growth factor, oestrogen and progesterone receptor expression in primary ovarian cancer: correlation with clinical outcome and response to chemotherapy.

The expression of epidermal growth factor receptor (EGFR), oestrogen receptor (ER) and progesterone receptor (PR) was assayed by a radioreceptor method in 117 primary ovarian cancers. EGFR was not significantly related to any of the clinicopathological parameters examined. In patients with stage II-IV disease who underwent second-look surgery after primary chemotherapy, a significant correlation between high EGFR levels and poor response to chemotherapy was demonstrated (P = 0.031). Moreover, post-operative residual tumour showed an independent role in predicting chemotherapy response (P = 0.0007) and EGFR status showed a borderline significance (P = 0.052) in the multivariate analysis. No correlation between steroid hormone receptors and clinicopathological parameters was observed. Whereas a significant relationship was shown between EGFR positivity and a shorter overall survival (OS) (P = 0.0022) and progression-free survival (PFS) (P = 0.0033), patient survival was not related to steroid hormone receptor status. Among the parameters tested only stage, ascites and EGFR status retained an independent prognostic value in the multivariate analysis

From the quantum transfer matrix to the quench action: the Loschmidt echo in XXZ Heisenberg spin chains

We consider the computation of the Loschmidt echo after quantum quenches in the interacting XXZ Heisenberg spin chain both for real and imaginary times. We study two-site product initial states, focusing in particular on the N\ue9el and tilted N\ue9el states. We apply the Quantum Transfer Matrix (QTM) approach to derive generalized TBA equations, which follow from the fusion hierarchy of the appropriate QTM's. Our formulas are valid for arbitrary imaginary time and for real times at least up to a time t0, after which the integral equations have to be modified. In some regimes, t0 is seen to be either very large or infinite, allowing to explore in detail the post-quench dynamics of the system. As an important part of our work, we show that for the N\ue9el state our imaginary time results can be recovered by means of the quench action approach, unveiling a direct connection with the quantum transfer matrix formalism. In particular, we show that in the zero-time limit, the study of our TBA equations allows for a simple alternative derivation of the recently obtained Bethe ansatz distribution functions for the N\ue9el, tilted N\ue9el and tilted ferromagnet states

Quasi-local conserved charges and spin transport in spin-1 integrable chains

We consider the integrable one-dimensional spin-1 chain defined by the Zamolodchikov-Fateev (ZF) Hamiltonian. The latter is parametrized, analogously to the XXZ spin-1/2 model, by a continuous anisotropy parameter and at the isotropic point coincides with the well-known spin-1 Babujian-Takhtajan Hamiltonian. Following a procedure recently developed for the XXZ model, we explicitly construct a continuous family of quasi-local conserved operators for the periodic spin-1 ZF chain. Our construction is valid for a dense set of commensurate values of the anisotropy parameter in the gapless regime where the isotropic point is excluded. Using the Mazur inequality, we show that, as for the XXZ model, these quasi-local charges are enough to prove that the high-temperature spin Drude weight is non-vanishing in the thermodynamic limit, thus establishing ballistic spin transport at high temperature

Aspectos nutricionais e fisiológicos em genótipos de soja com diferentes níveis de tolerância à restrição hídrica.

A fixação biológica de nitrogênio (FBN) é indispensável para a viabilidade da cultura da soja em termos econômicos e ambientais. Entretanto, a ocorrência de veranicos prejudica a cultura e a FBN. O objetivo desse trabalho foi avaliar aspectos nutricionais e fisiológicos em genótipos de soja com capacidade de manter a FBN em condições de restrição hídrica (30% CC), em comparação com a condição normal (70% CC). O experimento foi conduzido em delineamento inteiramente casualizado em esquema fatorial 5 × 2, com sete repetições, com as linhagens R01-581F, R01-416F, R02-1325, com capacidade de manter a FBN em condições de seca, e os padrões CD 215 e BRS 317, sob suprimento adequado de água (70% CC), ou sob restrição hídrica (30% CC) entre 45 e 55 dias. Avaliaram-se os teores de N e K na parte aérea, a taxa fotossintética e transpiratória das plantas, e a concentração de N-ureídos (alantoína + ácido alantóico) nos pecíolos e nódulos. Os genótipos R01-581F, R01-416F e R02-1325 apresentaram os maiores teores de N e K, independente da condição hídrica. A condição de 30% CC não influenciou no teor de K para os genótipos R01-518F, R01-416F e R02-1325. Apenas o genótipo R01-581F não apresentou diminuição da fotossíntese em condição de 30% CC, e teve a maior taxa transpiratória quando submetido à restrição hídrica. A 30% CC os genótipos R02-1325, CD 215 e BRS 317 tiveram aumento da concentração de N-ureídos em pecíolos, e para os nódulos, todos os genótipos aumentaram a concentração de N-ureídos nessa condição.Fertbio