Protection of parity-time symmetry in topological many-body systems: non-Hermitian toric code and fracton models

In the study of $\mathcal{P}\mathcal{T}$-symmetric quantum systems with non-Hermitian perturbations, one of the most important questions is whether eigenvalues stay real or whether $\mathcal{P}\mathcal{T}$-symmetry is spontaneously broken when eigenvalues meet. A particularly interesting set of eigenstates is provided by the degenerate ground-state subspace of systems with topological order. In this paper, we present simple criteria that guarantee the protection of $\mathcal{P}\mathcal{T}$-symmetry and, thus, the reality of the eigenvalues in topological many-body systems. We formulate these criteria in both geometric and algebraic form, and demonstrate them using the toric code and several different fracton models as examples. Our analysis reveals that $\mathcal{P}\mathcal{T}$-symmetry is robust against a remarkably large class of non-Hermitian perturbations in these models; this is particularly striking in the case of fracton models due to the exponentially large number of degenerate states.Comment: 20 pages, 6 figure

Empirical pricing kernels obtained from the UK index options market

Empirical pricing kernels for the UK equity market are derived as the ratio between risk-neutral densities, inferred from FTSE 100 index options, and historical real-world densities, estimated from time series of the index. The kernels thus obtained are almost compatible with a risk averse representative agent, unlike similar estimates for the US market

An exactly solvable dissipative spin liquid

Exactly solvable Hamiltonians with spin liquid ground states have proven to be extremely useful, not only because they unambiguously demonstrate that these phases can arise in systems of interacting spins but also as a pedagogical illustration of the concept and as a controlled starting point for further theoretical analysis. However, adding dissipative couplings to the environment - an important aspect for the realization of these phases - generically spoils the exact solvability. We here present and study a Lindbladian, describing a square-lattice spin-liquid with dissipative coupling to the environment, that admits an exact solution in terms of Majorana fermions coupled to static $\mathbb{Z}_2$ gauge fields. This solution allows us to characterize the steady-state solutions as well as ``quasiparticle'' excitations within the Lindbladian spectrum. This emergence of distinct types of quasiparticle excitations of the Lindbladian leads to a separation of timescales that govern the equilibration time of the expectation values of different classes of observables, some of which we identify as fractionalized string-like operators. This exactly solvable Lindbladian is expected to provide a starting point for a better understanding of the behavior of fractionalized systems under dissipative time evolution.Comment: 11 pages, 7 figure

Book Reviews

These are the book reviews from 1972

Symposium overview: Integrating cognitive, motivational, and sensory biases underlying acoustic- and multimodal-based mate choice

The goal of this symposium Integrating Cognitive, Motivational and Sensory Biases Underlying Acoustic and Multimodal-Based Mate Choice was to build a more complete framework in which to understand the mate choice brain. The presentations and papers within this symposium incorporate studies of motivational, cognitive, sensory and salience components of mate choice and highlight future directions that are needed to understand the biological basis of mate choice decision-making

Appetite for self-destruction: suicidal biting as a nest defense strategy in Trigona stingless bees

Self-sacrificial behavior represents an extreme and relatively uncommon form of altruism in worker insects. It can occur, however, when inclusive fitness benefits are high, such as when defending the nest. We studied nest defense behaviors in stingless bees, which live in eusocial colonies subject to predation. We introduced a target flag to nest entrances to elicit defensive responses and quantified four measures of defensivity in 12 stingless bee species in São Paulo State, Brazil. These included three Trigona species, which are locally known for their aggression. Species varied significantly in their attack probability (cross species range = 0–1, P < 0.001), attack latency (7.0–23.5 s, P = 0.002), biting duration of individual bees (3.5–508.7 s, P < 0.001), and number of attackers (1.0–10.8, P < 0.001). A “suicide” bioassay on the six most aggressive species determined the proportion of workers willing to suffer fatal damage rather than disengage from an intruder. All six species had at least some suicidal individuals (7–83 %, P < 0.001), reaching 83 % in Trigona hyalinata. Biting pain was positively correlated with an index of overall aggression (P = 0.002). Microscopic examination revealed that all three Trigona species had five sharp teeth per mandible, a possible defensive adaptation and cause of increased pain. Suicidal defense via biting is a new example of self-sacrificial altruism and has both parallels and differences with other self-sacrificial worker insects, such as the honey bee. Our results indicate that suicidal biting may be a widespread defense strategy in stingless bees, but it is not universal

Quantity and significance of wild meat off-take by a rural community in the Eastern Cape, South Africa

When compared to tropical forest zones in west and central Africa, off-take of wild meat from savannah and grassland biomes by local rural communities has not been well assessed. This case study of wild meat collection activities within a rural community in the Mount Frere region of the Eastern Cape (South Africa) uses last-catch records derived from 50 wild meat gatherers to calculate average off-take of taxa, species and fresh mass of wild meat per collection event. When per-event off take is overlaid onto household hunting frequency data, annual off-take would be 268.6 kg km−2 yr−1 or 3 kg person−1 yr−1 presuming constant off-take over an annual period. Monetary value of off-take would be South African R 307 (US$ 39) per household annually. For some species, off-take weight per km2 shows similar values to data from tropical forest zones, but high human population densities tend to dilute off-takes to less nutritionally significant amounts at the per person scale. However, unlike many tropical zones, none of the species harvested can be considered high-priority conservation species. Even densely populated and heavily harvested communal lands appear to offer high wild meat off-takes from low conservation priority species

First hospital outbreak of the globally emerging Candida auris in a European hospital

Background: Candida auris is a globally emerging multidrug resistant fungal pathogen causing nosocomial transmission. We report an ongoing outbreak of C. auris in a London cardio-thoracic center between April 2015 and July 2016. This is the first report of C. auris in Europe and the largest outbreak so far. We describe the identification, investigation and implementation of control measures. Methods: Data on C. auris case demographics, environmental screening, implementation of infection prevention/control measures, and antifungal susceptibility of patient isolates were prospectively recorded then analysed retrospectively. Speciation of C. auris was performed by MALDI-TOF and typing of outbreak isolates performed by amplified fragment length polymorphism (AFLP). Results: This report describes an ongoing outbreak of 50 C. auris cases over the first 16 month (April 2015 to July 2016) within a single Hospital Trust in London. A total of 44 % (n = 22/50) patients developed possible or proven C. auris infection with a candidaemia rate of 18 % (n = 9/50). Environmental sampling showed persistent presence of the yeast around bed space areas. Implementation of strict infection and prevention control measures included: isolation of cases and their contacts, wearing of personal protective clothing by health care workers, screening of patients on affected wards, skin decontamination with chlorhexidine, environmental cleaning with chorine based reagents and hydrogen peroxide vapour. Genotyping with AFLP demonstrated that C. auris isolates from the same geographic region clustered. Conclusion: This ongoing outbreak with genotypically closely related C. auris highlights the importance of appropriate species identification and rapid detection of cases in order to contain hospital acquired transmission

Perfil característico das atividades 17-hidroxilase e 17,20-liase reveladas por meio do metaboloma de esteroides urinários de pacientes com deficiência de CYP17

OBJECTIVES: (1) Characterize serum (S) and urinary (U) steroid metabolites in complete CYP17 deficiency (cCYP17D); (2) analyze the relative 17α-hydroxylase (17OH) and 17,20-lyase (17,20L) activities in vivo; and (3) comparedata from the two most prevalent mutations in Brazil. SUBJECTS AND METHODS: 20 genotyped cCYP17D patients from a previously reported cohort were homozygous for W406R or R362C; 11 controls were CYP17 wild types (WT). WT and cCYP17D patients had S and U samples drawn to measure: cortisol (F), corticosterone (B), deoxycorticosterone (DOC), 18OH-B, 18OH-DOC, and 17OHP; and tetrahydro (TH)-B, THA, THDOC, THF+5α-THF, TH-cortisone, androsterone, etiocholanolone, 5-pregnenediol, 17OH-pregnenolone and pregnanetriol. RESULTS: Compared to WT, cCYP17D patients had marked elevations of B, DOC, 18OH-B and 18OH-DOC, whereas 17OHP, F and adrenal androgens (AA) were reduced; U steroids parallel S findings. Metabolite ratios revealed that both 17OH and 17,20L activities were impaired in cCYP17D. There were nodifferences between W406R andR362C mutations. CONCLUSIONS: cCYP17D patients show parallel overproduction/overexcretion of 17-deoxysteroids, and marked reduction of F and AA. In addition to 17OH, 17,20-L activity was also impaired in cCYP17D. W406 and R362C mutations disclose similar Sand U patterns.OBJETIVOS: (1) Caracterizar os esteroides séricos (S) e urinários (U) na deficiência completa da CYP17 (DcCYP17); (2) analisar as atividades da 17α-hidroxilase (17OH) e 17,20-liase (17, 20 L) in vivo; e (3) comparar as duas mutações mais prevalentes no Brasil. SUJEITOS E MÉTODOS: 20 pacientes genotipados para a DcCYP17, de uma coorte anterior, eram homozigotos para W406R ou R362C (8 cada); 11 controles eram CYP17 wild types (WT). Amostras de S e U foram colhidas dos WT e pacientes para dosagem de: cortisol (F), corticosterona (B), deoxicorticosterona (DOC), 18-OH-B, 18OH-DOC e 17OHP; e tetraidro(TH)-B, THA, TH-DOC, THF+5α-THF, THE, androsterona, etiocolanolona, 5-pregnenediol, 17OH-pregnenolona e pregnanetriol. RESULTADOS: Comparados aos WT, os pacientes com DcCYP17 revelaram elevações acentuadas de B, DOC, 18OHB e 18OHDOC, enquanto 17OHP, F e andrógenos adrenais (AA) estavam reduzidos. Os esteroides na U acompanham os achados no S. As relações de metabólitos mostraram que as atividades de 17OH e 17,20L estavam reduzidas em pacientes com DcCYP17. Não houve diferenças entre pacientes com as mutações W406R e R362C. CONCLUSÕES: Na DcCYP17, a produção e a excreção dos 17-deoxiesteroides estão aumentadas em paralelo, em contraste com a reduzida produção/excreção de F e AA. As atividades da 17OH e 17,20-L estão diminuídas na DcCYP17. As mutações W406 e R362C apresentam achados semelhantes em S e U.Universidade Federal de São Paulo (UNIFESP) Department of Medicine Division of Endocrinology and MetabolismUniversity of Texas Southwestern Medical Center Department of Clinical SciencesUniversity of Birmingham Division of Medical SciencesUNIFESP, Department of Medicine Division of Endocrinology and MetabolismSciEL