281 research outputs found
Chiral symmetry breaking in the 3-d Thirring model for small
No full textWe study the dynamical breaking of chiral symmetry in the 3-d Thirring model for a small number of fermion species. The critical point is identified by fitting lattice data to an equation of state. The spectrum of the theory is studied to confirm the phase structure of the model
I piani paesaggistico-architettonici del Foro di E. Del Debbio. Dall’idea originaria (1928) al piano realizzato (1932-33) - DVD multimediale
No full textProdotto grafico multimediale incentrato sui progetti di Del Debbio per il Foro Mussolini dal 1928 al 1933, esposto alla Mostra "Enrico Del Debbio architetto. La misura della modernita'", (Galleria Nazionale d’Arte Moderna G.N.A.M., 7 dic. 2006 - 4 feb. 2007) promossa da DARC, MAXXI, in collab. con Direz. Reg. per i Beni Culturali e Paesaggistici del Lazio, Soprintendenza per i Beni architettonici e il paesaggio di Roma. (Cfr Colofon del Catalogo della Mostra di Neri M. L., "Enrico del Del Debbio", IdeaBooks, 2006). A seguito di accurati studi ed analisi e di specifiche ricostruzioni grafiche, tale sperimentazione multimediale ha inteso costituirsi quale modalità informativo-conoscitiva mirante a comunicare visivamente le matrici geometriche sottese, i sistemi degli assi visivi e funzionali, la rigorosa definizione dell’impianto urbano sempre presenti nell’evoluzione dei piani di Del Debbio
Bethe Ansatz solutions for highest states in SYM and AdS/CFT duality
No full textWe consider the operators with highest anomalous dimension in the compact rank-one sectors and of super Yang-Mills. We study the flow of from weak to strong 't Hooft coupling by solving (i) the all-loop gauge Bethe Ansatz, (ii) the quantum string Bethe Ansatz. The two calculations are carefully compared in the strong coupling limit and exhibit different exponents in the leading order expansion . We find and for the gauge or string solution. This strong coupling discrepancy is not unexpected, and it provides an explicit example where the gauge Bethe Ansatz solution cannot be trusted at large . Instead, the string solution perfectly reproduces the Gubser-Klebanov-Polyakov law . In particular, we provide an analytic expression for the integer level as a function of the U(1) charge in both sectors
Il Disegno del paesaggio. Il caso del Foro Mussolini
No full textL’argomento trattato si inquadra in una più ampia attività di studio e ricerca che ha individuato tra i suoi principali obiettivi scientifico-sperimentali quello di proporre modalità tecnologiche di indagine, approfondimento critico, manipolazione e comunicazione intorno al patrimonio architettonico con l’intento di generare positive ricadute relativamente alle modalità di organizzazione dei dati e di costituzione delle informazioni. In particolare l’articolo illustra alcuni esiti delle ricerche svolte in collegamento con le attività promosse dalla DARC nell’ambito della tutela degli archivi degli architetti del Novecento riguardanti, nello specifico, l’analisi del patrimonio documentario riguardante l’opera di Enrico Del Debbio. Scegliendo come caso-studio il Foro Mussolini a Roma, sono stati condotti accurati studi ed analisi sul materiale grafico messo a disposizione potendo giungere alla sperimentazione di un prodotto multimediale incentrato sulla rappresentazione e diffusione dei disegni di progetto e dove la costruzione dell’informazione è realizzata attraverso le modalità non lineari proprie
A surprise with many-flavor staggered fermions in the strong coupling limit
No full textIt is widely believed that chiral symmetry is spontaneously broken at zero temperature in the strong coupling limit of staggered fermions, for any number of colors and flavors. Using Monte Carlo simulations, we show that this conventional wisdom, based on a mean-field analysis, is wrong. For sufficiently many fundamental flavors, chiral symmetry is restored via a bulk, first-order transition. This chirally symmetric phase appears to be analytically connected with the expected conformal window of manyflavor continuum QCD. We perform simulations in the chirally symmetric phase at zero quark mass for various system sizes L, and measure the torelon mass and the Dirac spectrum. We find that all observables scale with L, which is hence the only infrared length scale. Thus, the strong-coupling chirally restored phase appears as a convenient laboratory to study IR-conformality. Finally, we present a conjecture for the phase diagram of lattice QCD as a function of the bare coupling and the number of quark flavors
Critical slowing down of topological modes
No full textWe investigate the critical slowing down of the topological modes using local
updating algorithms in lattice 2-d CP^(N-1) models. We show that the
topological modes experience a critical slowing down that is much more severe
than the one of the quasi-Gaussian modes relevant to the magnetic
susceptibility, which is characterized by with
. We argue that this may be a general feature of Monte Carlo
simulations of lattice theories with non-trivial topological properties, such
as QCD, as also suggested by recent Monte Carlo simulations of 4-d SU(N)
lattice gauge theories
theta dependence of SU(N) gauge theories
No full textWe study the theta dependence of four-dimensional SU(N) gauge theories, for N greater than or equal to 3 and in the large-N limit. We use numerical simulations of the Wilson lattice formulation of gauge theories to compute the first few terms of the expansion of the ground-state energy F(theta) around theta = 0, F(theta) - F(0) = A(2)theta(2) (1 + b(2)theta(2) + ...). Our results support Witten's conjecture: F(theta) - F(0) = Atheta(2) + O(1/N) for sufficiently small values of theta, theta < π. Indeed we verify that the topological susceptibility has a non-zero large-N limit χ(&INFIN;) = 2A with corrections of O(1/N-2), in substantial agreement with the Witten-Veneziano formula which relates χ(&INFIN;) to the η' mass. Furthermore, higher order terms in θ are suppressed; in particular, the O(θ(4)) term b(2) (related to η' - η' the elastic scattering amplitude) turns out to be quite small: b(2) = 0.023(7) for N = 3, and its absolute value decreases with increasing N, consistently with the expectation b(2) = O(1/N-2)
Topological susceptibility of SU(N) gauge theories at finite temperature
No full textWe investigate the large-N behavior of the topological susceptibility X in four-dimensional SU(N) gauge theories at finite temperature, and in particular across the finite-temperature transition at T-c. For this purpose, we consider the lattice formulation of the SU(N) gauge theories and perform Monte Carlo simulations for N = 4,6. The results indicate that X has a nonvanishing large-N limit for T T-c
Confining strings in representations with common n-ality
No full textWe study the spectrum of confining strings in SU(3) pure gauge theory, by means of lattice Monte Carlo simulations, using torelon operators in different representations of the gauge group. Our results provide direct evidence that the string spectrum is according to predictions based on n-ality. Torelon correlations in the rank-2 symmetric channel appear to be well reproduced by a two-exponential picture, in which the lowest state is given by the fundamental string sigma(1) = sigma, the heavier string state is such that the ratio sigma(2)/sigma(1) is approximately given by the Casimir ratio C-sym/C-f = 5/2, and the torelon has a much smaller overlap with the lighter fundamental string state
A model for string-breaking in QCD
No full textWe present a model for string breaking based on the existence of chromoelectric flux tubes. We predict the form of the long-range potential, and obtain an estimate of the string breaking length. A prediction is also obtained for the behaviour with temperature of the string breaking length near the deconfinement phase transition. We plan to use this model as a guide for a program of study of string breaking on the lattice
- …
