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Mesons from global anti-de Sitter space
Get PDFIn the context of gauge/gravity duality, we study both probe D7– and probe D5–branes in global Anti-de Sitter space. The dual field theory is N = 4 theory on R × S^3 with added flavour. The branes undergo a geometrical phase transition in this geometry as function of the bare quark mass m_q in units of 1/R with R the S^3 radius. The meson spectra are obtained from fluctuations of the brane probes. First, we study them numerically for finite quark mass through the phase transition. Moreover, at zero quark mass we calculate the meson spectra analytically both in supergravity and in free field theory on R × S^3 and find that the results match: For the chiral primaries, the lowest level is given by the zero point energy or by the scaling dimension of the operator corresponding to the fluctuations, respectively. The higher levels are equidistant. Similar results apply to the descendents. Our results confirm the physical interpretation that the mesons cannot pair-produce any further when their zero-point energy exceeds their binding energy
Magnetic Catalysis of Chiral Symmetry Breaking: A Holographic Prospective
Get PDFWe review a recent investigation of the effect of magnetic catalysis of mass generation in holographic Yang-Mills theories. We aim at a self-contained and pedagogical form of the review. We provide a brief field theory background and review the basics of holographic flavordynamics. The main part of the review investigates the influence of external magnetic field on holographic gauge theories dual to the D3/D5– and D3/D7– brane intersections. Among the observed phenomena are the spontaneous breaking of a global internal symmetry, Zeeman splitting of the energy levels and the existence of pseudo Goldstone modes. An analytic derivation of the Gell-Mann–Oaks–Renner relation for the D3/D7 set up is reviewed. In the D3/D5 case the pseudo Goldstone modes satisfy non-relativistic dispersion relation. The studies reviewed confirm the universal nature of the magnetic catalysis of mass generation
Anick-type Resolutions and Consecutive Pattern Avoidance
Get PDFFor permutations avoiding consecutive patterns from a given set, we present a combinatorial formula for the multiplicative inverse of the corresponding exponential generating function. The formula comes from homological algebra considerations in the same sense as the corresponding inversion formula for avoiding word patterns comes from the well known Anick’s resolution
Dynamical models for the formation of elephant trunks in H ii regions
Get PDFThe formation of pillars of dense gas at the boundaries of H ii regions is investigated with hydrodynamical numerical simulations including ionizing radiation from a point source. We show that shadowing of ionizing radiation by an inhomogeneous density field is capable of forming so-called elephant trunks (pillars of dense gas as in e.g. M16) without the assistance of self-gravity or of ionization front and cooling instabilities. A large simulation of a density field containing randomly generated clumps of gas is shown to naturally generate elephant trunks with certain clump configurations. These configurations are simulated in isolation and analysed in detail to show the formation mechanism and determine possible observational signatures. Pillars formed by the shadowing mechanism are shown to have rather different velocity profiles depending on the initial gas configuration, but asymmetries mean that the profiles also vary significantly with perspective, limiting their ability to discriminate between formation scenarios. Neutral and molecular gas cooling are shown to have a strong effect on these results
Tuileagna Ó Maoil Chonaire and the Book of Pottlerath
Get PDFThe significance of St Patrick s College Maynooth MS C112(d) for the history of the visit by Tuileagna Ó Maoil Chonaire to the Bodleian Library in 1673, with remarks on aspects of textual histor
Captain Somhairle and His Books Revisited
Get PDFA study of the career of Somhairle Mac Domhnaill, for whom the Book of the O'Conor Don was compiled, and the political and cultural context of its compilation