Instanton confinement-deconfinement transitions: The stability of pseudogap phases and topological order

We explore the stability of certain many-body quantum states which may exist at zero or finite temperatures, may lack long-range order and even topological order, and still are thermodynamically distinct from uncorrelated disordered phases. We sharply characterize such states by the conservation of topological charge, or equivalently confinement of instantons, using a generalization of the Wilson loop and the correlation length of an emergent gauge field. Our main conclusions are: (i) topological orders can exist at finite temperatures, (ii) relativistic liquids of topological defects can also exist as stable phases at finite temperatures, and (iii) there are two universality classes of instanton suppression. We also relate the instanton dynamics to the problem of the pseudogap state in underdoped cuprates. A universal experimental signature of the instanton deconfinement transition is a change of the quantum noise spectrum, which can perhaps be measured in some situations, for example via a quantum anomaly, or indirectly detected with a specific heat jump. The method of analysis is a functional renormalization group that generalizes the Coulomb gas treatment of Kosterlitz and Thouless to arbitrary interactions and dimensions. In particular, we construct an exact non-perturbative technique for confining interactions between instantons, which introduce irreparable infra-red divergences in the standard perturbative approaches.Comment: 20 pages, 2 figure

Unitarity in periodic potentials: a renormalization group analysis

We explore the universal properties of interacting fermionic lattice systems, mostly focusing on the development of pairing correlations from attractive interactions. Using renormalization group we identify a large number of fixed points and show that they correspond to resonant scattering in multiple channels. Pairing resonances in finite-density band insulators occur between quasiparticles and quasiholes living at different symmetry-related wavevectors in the Brillouin zone. This allows a BCS-BEC crossover interpretation of both Cooper and particle-hole pairing. We show that in two dimensions the run-away flows of relevant attractive interactions lead to charged-boson-dominated low energy dynamics in the insulating states, and superfluid transitions in bosonic mean-field or XY universality classes. Analogous phenomena in higher dimensions are restricted to the strong coupling limit, while at weak couplings the transition is in the pair-breaking BCS class. The models discussed here can be realized with ultra-cold gases of alkali atoms tuned to a broad Feshbach resonance in an optical lattice, enabling experimental studies of pairing correlations in insulators, especially in their universal regimes. In turn, these simple and tractable models capture the emergence of fluctuation-driven superconducting transitions in fermionic systems, which is of interest in the context of high temperature superconductors.Comment: 16 pages, 6 figures, published versio

s-wave Cooper pair insulators and theory of correlated superconductors

The pseudogap state of cuprate high-temperature superconductors has been often viewed as either a yet unknown competing order or a precursor state to superconductivity. While awaiting the resolution of the pseudogap problem in cuprates, we demonstrate that local pairing fluctuations, vortex liquid dynamics and other precursor phenomena can emerge quite generally whenever fermionic excitations remain gapped across the superconducting transition, regardless of the gap origin. Our choice of a tractable model is a lattice band insulator with short-range attractive interactions between fermions in the s-wave channel. An effective crossover between Bardeen-Cooper-Schrieffer (BCS) and Bose-Einstein condensate (BEC) regimes can be identified in any band insulator above two dimensions, while in two dimensions only the BEC regime exists. The superconducting transition is "unconventional" (non-pair-breaking) in the BEC regime, identified by either the bosonic mean-field or XY universality class. The insulator adjacent to the superconductor in the BEC regime is a bosonic Mott insulator of Cooper pairs, which may be susceptible to charge density wave ordering. We construct a function of the many-body excitation spectrum whose non-analytic changes define a sharp distinction between band and Mott insulators. The corresponding "second order transition" can be observed out of equilibrium by driving a Cooper pair laser in the Mott insulator. We explicitly show that the gap for charged bosonic excitations lies below the threshold for Cooper pair breakup in any BEC regime, despite quantum fluctuations. Our discussion ends with a view of possible consequences for cuprates, where antinodal pair dynamics has certain features in common with our simple s-wave picture.Comment: 18 pages, 4 figures, published versio

Social Media Interactions and Online Games - Building up New Human Relationships in Danube Region

In this paper we are trying to explore possibilities of using online environment,multiplayer gaming culture and social media networks to engage people in the DanubeRegion around social, multi-cultural and environment initiatives. The Danube Region onlinecommunity could become a new cultural phenomena, technology mediated, built on humaninteractions, common interests and cultural heritage which open space for future humancenteredsocial and infrastructural design initiatives. We believe that such social mediaenvironment could also be a research playground where people form Danube Region mayexpress their needs and desires as well as to leave the trace of their behavior, significant forfurther Danube Region development

Percepcija bola, socijalna i funkcionalna nelagodnost tokom ortodontske terapije

Introduction/Objective Pain and social discomfort are common experiences after the insertion of a fixed orthodontic appliance. The aim of the study was to determine the intensity of pain during the first seven days after the placement of a fixed orthodontic appliance, the impact of orthodontic treatment on psychosocial component of the patient and daily life activities in the first month of therapy. Methods The study included 60 randomly selected patients from the Department of Orthodontics, Faculty of Dental Medicine, Belgrade, Serbia, aged 15 to 20 years. After the insertion of a fixed orthodontic appliance, the patients were given a questionnaire form comprising questions related to the intensity of pain in the first seven days, function of speech and chewing, oral hygiene, injury of the oral mucosa, and social contacts. For the processing of results obtained from the questionnaire χ2 test was used. Results The largest percentage of respondents (21.7%) rated pain with grade 1, while less than 10% of respondents gave grades 4, 6, 7, 9, and 10. Most of the participants (95%) answered that they had no difficulties with daily life activities caused by the fixed orthodontic appliance. Most respondents (91.7%) did not have any social discomfort, while a small percentage (8.3%) said they had these problems. Conclusion General intensity of pain that respondents felt during the first seven days after the placement of a fixed orthodontic appliance was low to moderate. For most of the respondents there was no change in social behavior related to the psychosocial component. Except for changes in dietary habits and sores on the oral mucosa of the cheek in the first month of therapy, examines had no major problems with daily life activities.Uvod/Cilj Bol i nelagodnost su uobičajena iskustva nakon postavljanja fiksnog ortodontskog aparata. Cilj ovog rada je odrediti intenzitet bola tokom prvih sedam dana nakon postavljanja fiksnog ortodontskog aparata, uticaj ortodontske terapije na psihosocijalnu komponentu ličnosti i svakodnevne životne aktivnosti u prvom mesecu terapije. Metode U istraživanju je učestvovalo 60 nasumično izabranih pacijenata Klinike za ortopediju vilica Stomatološkog fakulteta u Beogradu, uzrasta od 15 do 20 godina. Po postavljanju fiksnog ortodontskog aparata pacijenti su dobili da popune upitnik i odgovore na pitanja koja su se odnosila na pojavu bola u prvih sedam dana po postavljanju aparata na skali od jedan do deset, pitanja vezana za funkciju govora i žvakanja, održavanje oralne higijene, povrede oralne sluzokože i socijalne kontakte. Za obradu rezultata dobijenih iz anketnog upitnika koristio se χ2 test. Rezultati Najveći procenat ispitanika (21,7%) ocenili su bol sa ocenom 1 (nisu osećali bol tokom prvih sedam dana), dok je manje od 10% dalo ocene 4, 6, 7, 9 i 10. Većina učesnika (95%) odgovorila je da nisu imali problema sa obavljanjem svakodnevnih životnih aktivnosti zbog fiksnog ortodontskog aparata. Većina ispitanika (91,7%) nisu osećali socijalnu nelagodnost, a 8,3% jeste. Zaključak Generalni intenzitet bola koji su ocenili ispi- tanici prvih sedam dana po postavljanju fiksnog ortodontskog aparata je bio nizak do umeren. Kod većine ispitanika nije bilo promena u psihosocijalnom ponašanju. Osim promena navika u ishrani i pojave ranica na unutrašnjoj strani obraza u prvih mesec dana terapije, ispitanici nisu imali problema sa obavljanjem svakodnevnih aktivnosti