1,721,013 research outputs found
Introduction to Complex Numbers
Full text linkThis is an introduction to the mathematics of complex numbers, starting from the very basics of their definitions, up to proving theorems for polynomials. The text covers everything required of most first-year mathematics courses on complex numbers with proofs, where appropriate
QCD physics from the AdS/CFT correspondence
No full textEThOS - Electronic Theses Online ServiceGBUnited Kingdo
Towards a perfect QCD gravity dual
No full textMany examples of gravitational duals exist of theories that are highly supersymmetric and conformal in the UV yet have the same massless states as QCD. We discuss such theories with an explicit UV cutoff and propose that, by tuning higher dimension operators at the cutoff by hand, the effects of the extra matter states in the UV may be removed from the IR physics. We explicitly work in the AdS–Schwarzschild description of QCD4 and tune the operator TrF4 by relaxing the near horizon limit to reproduce the lattice 0++ glueball mass results. We find that to reproduce the lattice data, the IR and UV cutoffs lie close to each other and there is essentially no AdS-like period between them. The improved geometry gives a better match to the lattice data for 0?+ glueball masses
Chiral dynamics from AdS space
No full textWe study the low energy dynamics of pions in a gravity dual of chiral symmetry breaking. The string theory construction consists of a probe D7 brane in the Constable-Myers nonsupersymmetric background, which has been shown to describe chiral symmetry breaking in the pattern of QCD. We expand the D7 brane's Dirac-Born-Infeld action for fluctuations that correspond to the Goldstone mode and show that they take the form of a nonlinear chiral Lagrangian. We numerically compute the quark condensate, pion decay constant, and higher order Gasser-Leutwyler coefficients. We find their form is consistent with naive dimensional analysis estimates. We also explore the gauging of the quark's chiral symmetries and the vector meson spectrum. <br/
Chiral phase transitions and quantum critical points of the D3/D7(D5) system with mutually perpendicular E and B fields at finite temperature and density
No full textWe study chiral symmetry restoration with increasing temperature and density in gauge theories subject to mutually perpendicular electric and magnetic fields using holography. We determine the chiral symmetry breaking phase structure of the D3/D7 and D3/D5 systems in the temperature-density-electric field directions. A magnetic field may break the chiral symmetry and an additional electric field induces Ohm and Hall currents as well as restoring the chiral symmetry. At zero temperature the D3/D5 system displays a line of holographic BKT phase transitions in the density-electric field plane, while the D3/D7 system shows a mean-field phase transition. At intermediate temperatures, the transitions in the density-electric field plane are of first order at low density, transforming to second order at critical points as density rises. At high temperature the transition is only ever first order
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Finite system size effects on the effective coupling in scalar quantum field theory
Full text linkFindings from the Large Hadron Collider (LHC) provide evidence that quark-gluon plasma (QGP) formation , traditionally associated with large nucleus-nucleus collisions, also emerges in high multiplicity proton-proton (p + p) and proton-nucleus (p + A) collisions. It has also been shown that azimuthal correlations of low transverse momentum outgoing particles from these high multiplicity p + p and p + A collisions can be modeled well using nearly inviscid relativistic hydrodynamics. One would expect the equation of state (EOS) used in such hydrodynamic simulations to receive significant contributions in systems of size characteristic of p+p collisions. Indeed it has been shown that free scalar thermal field theory receives ∼ 40% corrections to the usual thermodynamic quantities when confined using Dirichlet boundary conditions with characteristic lengths set by central p + p collisions. Furthermore, the potential importance of asymmetric system sizes has also been highlighted in quenched lattice QCD calculations using periodic boundary conditions. In order to analyse the finite system size corrections to the QCD EOS, we need to explore the finite system size corrections to the running of the QCD coupling. This thesis provides a first step toward such a calculation. We consider massive scalar ϕ 4 theory in a spacetime with periodic boundary conditions. We allow characteristic lengths to be asymmetric, or even infinite. We first recount the infinite volume NLO 2 → 2 scattering amplitude calculation using dimensional regularisation, and then introduce and employ denominator regularisation. We then perform the non-trivial calculation of the NLO 2 → 2 scattering amplitude in our compactified spacetime. This requires the derivation of an new analytic continuation of the generalised Epstein zeta function after employing denominator regularisation in order to isolate the UV divergence. Denominator regularisation is necessary, since the usual techniques in dimensional regularisation no longer applies when we allow asymmetric characteristic lengths. We confirm that taking the limit of infinite characteristic lengths yields the usual infinite space-time result. We then perform another non-trivial self-consistency check by verifying that the NLO 2 → 2 Page ii scattering amplitude satisfies unitarity in the form of the optical theorem, regardless of the number of compactified dimensions. In order to show this we derived a generalisation of a formula originally proposed by Hardy and Ramanujan, and interpret its analytic continuation in the context of Abel summation. We numerically explore the scattering amplitude in some special cases, but find the s-channel of the 2 compactified dimension case to be numerically ill-behaved. We then derive and employ a dispersion relation in order to numerically explore the s-channel. Using the Callan-Symanzik equation to derive the beta function, we find it insensitive to finite system effects, which only modifies the IR. We then perform a geometric resummation of bubble diagrams, and show that the running coupling from the beta function agrees to a leading log in energy to the resummed amplitude. Interpreting the modulus of the resummed amplitude as an effective coupling in analogy to QED, we numerically explore its dependence on energy scale as well as the length scale of the system. We find that surprisingly at small length scales the effective coupling decreases, even though the beta function is positive. This thesis has overlap with related work by the author
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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