2,780 research outputs found
Lattice-Renormalization of the Polyakov Loop
Get PDFZantow F. Lattice-Renormalization of the Polyakov Loop. Bielefeld: Fakultät für Physik; 2003
GHOST COHOMOLOGIES AND HIDDEN SPACE–TIME SYMMETRIES
No full textWe observe and study new nonlinear global space-time symmetries of the full ghost + matter action of RNS superstring theory. We show that these surprising new symmetries are generated by the special worldsheet currents (physical vertex operators) of RNS superstring theory, violating the equivalence of superconformal ghost pictures. We review the questions of BRST-invariance and nontriviality of picture-dependent vertex operators and show their relation to hidden space-time symmetries and hidden space-time dimensions. In particular, we relate the space-time transformations, induced by picture-dependent currents, to the symmetries observed in the 2T physics approach. © World Scientific Publishing Company.Bars I, 1999, PHYS REV D, V59, DOI 10.1103-PhysRevD.59.045019; Bars I, 1999, PHYS REV D, V59, DOI 10.1103-PhysRevD.59.125004; Bars I, 1999, PHYS LETT B, V457, P275, DOI 10.1016-S0370-2693(99)00582-1; KLEBANOV IR, 1991, MOD PHYS LETT A, V6, P3273, DOI 10.1142-S021773239100378X; KLEBANOV IR, 1993, PHYS REV LETT, V71, P3243, DOI 10.1103-PhysRevLett.71.3243; Kogan II, 2003, INT J MOD PHYS A, V18, P1827, DOI 10.1142-S0217751X03013715; LIAN BH, 1991, PHYS LETT B, V254, P417, DOI 10.1016-0370-2693(91)91177-W; Polyakov D, 2005, INT J MOD PHYS A, V20, P2603, DOI 10.1142-S0217751X05020999; Polyakov D, 2002, PHYS REV D, V65, DOI 10.1103-PhysRevD.65.084041; POLYAKOV D, IN PRESS INT J MOD P; Polyakov D, 2005, INT J MOD PHYS A, V20, P4001, DOI 10.1142-S0217751X05024274; VERLINDE E, 1987, PHYS LETT B, V192, P95, DOI 10.1016-0370-2693(87)91148-8; WITTEN E, 1992, NUCL PHYS B, V373, P187, DOI 10.1016-0550-3213(92)90454-J57
Improved hadronic measurements and spectral sums on the lattice
No full textIn this thesis we address several topics of lattice QCD.
As a first project we perform calculations of ground and excited states of light mesons. Especially the extraction of the excited states turns out be very difficult. Therefore we utilize the variational method, which requires the construction of a rich basis of different interpolating fields, i.e., lattice discretized operators which have the same quantum number as the desired states. To build such a basis we consider quarks with different spatial wavefunctions, including some that mimic orbital excitations.
In the second project, we develop a new improvement scheme to compute estimates of all-to-all quark propagators, i.e., quark propagators which connect each point on the lattice to all others. For that purpose we decompose the lattice in two disjoint regions or domains which allows to significantly reduce the amount of random variables used in the estimation process. As a first major application of this improvement scheme, we compute the spectrum of heavy-light hadrons, i.e., hadrons containing one very heavy quark (bottom) and one or more light quarks (up, down, strange). To reduce the computational costs for the heavy quark, we describe it by means of the lowest order of heavy quark effective theory and thus treat it as infinitely heavy. From our calculations we are able to extract several ground and excited meson states and even a number of baryon ground states.
In the last project, we study two very important features of QCD: Confinement and spontaneous breaking of chiral symmetry. Both of them are temperature dependent: As the temperature is increased above a critical value, the theory becomes deconfined and chiral symmetry is restored. The temperature, at which these phase transitions take place, is approximately the same at least for zero baryon density. To study a possible connection between these phenomena, we try to relate the order parameters of the phase transitions.
In pure Yang-Mills theory the order parameter for the confinement-deconfinement transition is the Polyakov loop. The order parameter for the spontaneous breaking of chiral symmetry is given by the chiral condensate, which is related to the eigenvalues of the Dirac operator. It has been shown that also the Polyakov loop can be expressed in terms of these eigenvalues, as a spectral sum. In a first step we perform a numerical study of these sums. We find that the ordinary Polyakov loop is governed by the ultraviolet modes of the Dirac operator. Therefore, in a second step we define a new order parameter for confinement, the "dressed Polyakov loop". This quantity has two advantages: It can be expressed as a spectral sum which has a better convergence behavior (infrared dominated) and it is closely related to the quark condensate via a Fourier transformation. Also the spectral sums for the dressed Polyakov loop are investigated numerically
On Polyakov's basic variational formula for loop spaces
No full textWe use the homological algebra context to give a more rigorous proof of Polyakov's basic variational formula for loop spaces
GL(1) charged states in twistor string theory
No full textWe discuss the appearance of the GL(1) charged physical operators in the twistor string theory. These operators are shown to be BRST-invariant and non-trivial and some of their correlators and conformal β-functions are computed. Remarkably, the non-conservation of the GL(1) charge in interactions involving these operators, is related to the anomalous term in the Kac-Moody current algebra. While these operators play no role in the maximum helicity violating (MHV) amplitudes, they are shown to contribute non-trivially to the non-MHV correlators in the presence of the worldsheet instantons. We argue that these operators describe the non-perturbative dynamics of solitons in conformal supergravity. The exact form of such solitonic solutions is yet to be determined. © 2005 Published by Elsevier B.V.Azcarraga J., 1989, PHYS REV LETT, V3, P2443; Berkovits N., 2004, JHEP, V0404; Berkovits N., 2004, JHEP, V0408, P009; CACHAZO F, 2004, JHEP, V410; Gubser SS, 1998, PHYS LETT B, V428, P105, DOI 10.1016-S0370-2693(98)00377-3; Maldacena J M, 1998, ADV THEOR MATH PHYS, V2, P231, DOI DOI 10.1023-A:1026654312961; POLYAKOV D, HEPTH0406079; POLYAKOV D, IN PRESS INT J MOD P; Witten E., 1998, ADV THEOR MATH PHYS, V2, P253, DOI DOI 10.1016-S0370-1573(99)00083-6; Witten E., HEPTH9112056; Witten E, 2004, COMMUN MATH PHYS, V252, P189, DOI 10.1007-s00220-004-1187-344
POLYAKOV LOOPS AND FINITE-SIZE EFFECTS OF HADRON MASSES IN FULL LATTICE QCD
No full textPolyakov type loops are responsible for the difference between quenched and unquenched finite size effects on the QCD mass spectrum. With a numerical simulation, using appropriate sea quark spatial boundary conditions, we show that we can align the phases of spatial Polyakov loops in a predefined direction. Starting from these results, we propose a procedure to minimize fluctuations due to these effects in meson propagators. © 1995
Geração radiativa de repulsão vetorial para quarks leves
Get PDFDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2014Abstract: We apply a non-perturbative analytical method, known as the Optimized PerturbationTheory (OPT), to the Polyakov-Nambu-Jona-Lasinio (PNJL) model in order to investigate physical quantities associated with the QCD phase transitions. We consider the Taylor expansion of the pressure in powers of µ/T obtaining the second cumulant (c2) which is associated to the quark number susceptibility. We discuss how the OPT nite Nc radiative (quantum) corrections induce a contribution to the pressure which behaves as a vector repulsion even when such a channel is absent in the original classical potential. Our results are then compared with the ones furnished by lattice QCD simulations and by the large-Nc approximation showing that, physically, the OPT results resemble those furnished by the latter approximation when a repulsive vector channel is explicitly included in the classical potential. In this case, both approximations fail to correctly describe the Stefan-Boltzmann limit at high temperatures. We discuss how this problem can be circumvented by taking the couplings to be temperature dependent so as to simulate the phenomenon of asymptotic freedom. Since this is the first time the OPT is applied to the PNJL we also discuss many technicalities associated with the evaluation of two loop (exchange) diagrams.Neste trabalho o método analítico não perturbativo conhecido como Teoria de Perturbação Otimizada (OPT) é aplicada ao modelo de Polyakov-Nambu-Jona-Lasinio (PNJL) para que quantidades físicas, associadas com as transições de fase da QCD, possam ser calculadas. A expansão da pressão em potências de µ/T é considerada para obter o segundo cumulante (c2) que é uma quantidade relacionada com a susceptibilidade do número de quarks. Primeiramente discutimos como as correções radiativas de Nc finito geradas pela OPT produzem uma contribuição que se comporta como um termo vetorial repulsivo mesmo quando este tipo de canal está ausente no potencial clássico original. Em seguida, nossos resultados são comparados com aqueles fornecidos pelas simulações na rede e também pela aproximação de Nc grande(LN). Fisicamente, os resultados da OPT são similares aqueles fornecidos pela aproximação LN quando um canal vetorial repulsivo é explicitamente incluido no potencial clássico. Neste caso, nenhuma destas aproximações analíticas produz corretamente o limite de Stefan Boltzmann para altas temperaturas. Contudo, nossos resultados sugerem como estes problemas podem ser contornados tomando-se as constantes de acoplamento como sendo dependentes da temperatura, de maneira que o fenômeno da liberdade assimptótica possa ser simulado. Esta é a primeira vez que a OPT é aplicada ao modelo de PNJL e por isto vários aspectos técnicos relacionados com o cálculo de diagramas de dois laços são também aqui apresentados
Is Sustainable Development of Deserts Feasible?
Get PDFHot deserts that presently cover about one-fifth of the land area of our planet are rapidly devouring more and more arable lands mostly due to anthropogenic causes. We propose an interdisciplinary approach to revitalizing and commercializing hot deserts, which is based on systems thinking and Russian and NASA space technology experience in designing life-support systems for long-duration flights. We formulate ten principles for the design of sustainable life support systems in deserts, which can make the development of the deserts feasible. It is discussed how the principles can be employed to design and operate desert’s eco-industrial parks with greenhouses in which the transpired and evaporated moisture is collected and condensed. The potential benefits of setting up the eco-industrial parks in deserts include the slowdown and eventual reversal of the desertification trend, the migration of many industrial production facilities from mild-climate regions to deserts, the increased availability of potable water and food in deserts, the development of poor African countries, and the emergence of new investment markets
Gittersimulation einer zentrumssymmetrischen dreidimensionalen effektiven Theorie für SU(2) Yang-Mills
No full textWe present lattice simulations of a center symmetric dimensionally reduced effective field theory for SU(2) Yang Mills which employ thermal Wilson lines and three-dimensional magnetic fields as fundamental degrees of freedom. The action is composed of a gauge invariant kinetic term, spatial gauge fields and a potential for the Wilson line which includes a "fuzzy" bag term to generate non-perturbative fluctuations between Z(2) degenerate ground states. The model is studied in the limit where the gauge fields are set to zero as well as the full model with gauge fields. We confirm that, at moderately weak coupling, the "fuzzy" bag term leads to eigenvalue repulsion in a finite region above the deconfining phase transition which shrinks in the extreme weak-coupling limit. A non-trivial Z(N) symmetric vacuum arises in the confined phase. The effective potential for the Polyakov loop in the theory with gauge fields is extracted from the simulations including all modes of the loop as well as for cooled configurations where the hard modes have been averaged out. The former is found to exhibit a non-analytic contribution while the latter can be described by a mean-field like ansatz with quadratic and quartic terms, plus a Vandermonde potential which depends upon the location within the phase diagram. Other results include the exact location of the phase boundary in the plane spanned by the coupling parameters, correlation lengths of several operators in the magnetic and electric sectors and the spatial string tension. We also present results from simulations of the full 4D Yang-Mills theory and attempt to make a qualitative comparison to the 3D effective theory.Diese Arbeit präsentiert die Ergebnisse der Gittersimulation einer dreidimensionalen effektiven Theorie für eine SU(2) Eichtheorie bei endlichen Temperaturen. Die Theorie verwendet thermische Wilson Linien und den dreidimensionalen magnetischen Sektor als elementare Freiheitsgrade. Die Wirkung der effektiven Theorie respektiert alle Symmetrien der Eichtheorie in vier Dimensionen. Sie ist invariant unter lokalen SU(2) Eichtransformationen und zusätzlich invariant unter globalen Z(2) Transformationen, welche dem Abel'schem Zentrum der SU(2) Gruppe entsprechen. Sie enthält das Quadrat des dreidimensionalen Feldstärketensors, einen effektiven kinetischen Term der die Eichfelder an die Wilson Linien koppelt und das störungstheoretische Potential der Wilson Linien bis zur ersten Ordnung. Zusätzlich wird ein "fuzzy bag'' Term addiert, welcher einen Phasenübergang erzeugt und nicht-störungstheoretische Fluktuationen zwischen Z(2) symmetrischen Grundzuständen generiert. Wir untersuchen die Theorie sowohl im Grenzfall verschwindender Magnetfelder, als auch die volle Theorie in welcher dynamische Magnetfelder auftreten. Wir zeigen, dass die Theorie eine Phase mit spontan gebrochener Z(2) Symmetrie besitzt in welcher der Polyakov Loop einen nicht-verschwindenden Wert hat. In Analogie zur Quantenchromodynamik entspricht dies einer Aufhebung des Quark-Confinement. Wir bestimmen das Phasendiagramm der Theorie und ermitteln die Ordnung des Phasenübergangs an verschiedenen Stellen der Phasengrenze mittels Korrelationsfunktionen und des Skalenverhaltens der Suszeptibilität. Wir zeigen dass im Bereich mittel schwacher Kopplung nahe der Phasengrenze in der Symmetrie-gebrochenen Phase der "fuzzy bag'' Term Eigenwert Repulsion erzeugt, welche im Grenzfall extrem schwacher Kopplung verschwindet. Wir zeigen dass ein nicht-triviales Z(2) symmetrisches Vakuum existiert. Für die volle Theorie mit Eichfeldern untersuchen wir die räumliche String Spannung und zeigen dass magnetische Observablen vom elektrischen Sektor nur schwach beeinflusst werden. Desweiteren bestimmen wir das effektive Potential des Polyakov Loop, sowohl für den Fall dass alle Fourier Moden betrachtet werden, als auch für "gekühlte'' Konfigurationen ("Block Spins'') in welchen das Polyakov Loop Feld über kleine Volumina gemittelt wird, wodurch kurzreichweitige Fluktuationen unterdrückt werden. Qualitative Vergleiche mit der vierdimensionalen Eichtheorie zeigen dass das Verhalten des Block Spin Potentials in der dreidimensionalen Theorie mit der vierdimensionalen Theorie übereinstimmt
Study of QCD-like theories at nonzero temperatures and densities
No full textIn this thesis I use effective models to investigate the properties of QCD-like theories at nonzero temperature and baryon chemical potential. First I construct a PNJL model using a lattice spin model with nearestneighbor interactions for the gauge sector and four-fermion interactions for the quarks in (pseudo)real representations of the gauge group. Calculating the phase diagram in the plane of temperature and quark chemical potential in QCD with adjoint quarks, it is qualitatively confirmed that the critical temperature of the chiral phase transition is much higher than the deconfinement transition temperature. At a chemical potential equal to half of the diquark mass in the vacuum, a diquark Bose–Einstein condensation (BEC) phase transition occurs. In the two-color case, a Ginzburg–Landau expansion is used to study the tetracritical behavior around the intersection point of the deconfinement and BEC transition lines which are both of second order. A compact expression for the expectation value of the Polyakov loop in an arbitrary representation of the gauge group is obtained for any number of colors, which allows us to study Casimir scaling at both nonzero temperature and chemical potential. Subsequently I study the thermodynamics of two-color QCD (QC2D) at high temperature and/or density using ZQCD, a dimensionally reduced superrenormalizable effective theory, formulated in terms of a coarse grained Wilson line. In the absence of quarks, the theory is required to respect the Z2 center symmetry, while the effects of quarks of arbitrary masses and chemical potentials are introduced via soft Z2 breaking operators. Perturbative matching of the effective theory parameters to the full theory is carried out explicitly, and it is argued how the new theory can be used to explore the phase diagram of two-color QCD
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