30 research outputs found
Comments on Holographic Entanglement Entropy and RG Flows
Using holographic entanglement entropy for strip geometry, we construct a
candidate for a c-function in arbitrary dimensions. For holographic theories
dual to Einstein gravity, this c-function is shown to decrease monotonically
along RG flows. A sufficient condition required for this monotonic flow is that
the stress tensor of the matter fields driving the holographic RG flow must
satisfy the null energy condition over the holographic surface used to
calculate the entanglement entropy. In the case where the bulk theory is
described by Gauss-Bonnet gravity, the latter condition alone is not sufficient
to establish the monotonic flow of the c-function. We also observe that for
certain holographic RG flows, the entanglement entropy undergoes a 'phase
transition' as the size of the system grows and as a result, evolution of the
c-function may exhibit a discontinuous drop.Comment: References adde
Scale without Conformal Invariance: Theoretical Foundations
We present the theoretical underpinnings of scale without conformal
invariance in quantum field theory. In light of our results the gradient-flow
interpretation of renormalization-group (RG) flow is challenged, due to deep
connections between scale-invariant theories and recurrent behaviors in the RG.
We show that, on scale-invariant trajectories, there is a redefinition of the
dilatation current that leads to generators of dilatations that generate
dilatations. Finally, we develop a systematic algorithm for the search of
scale-invariant trajectories in perturbation theory.Comment: 18 pages. Added note to make clear that the results of
arXiv:1106.2540 do not imply the existence of unitary theories with scale but
without conformal invariance in perturbation theory in
spacetime dimension
Influence of freeze-thaw events on carbon dioxide emission from soils at different moisture and land use
BACKGROUND: The repeated freeze-thaw events during cold season, freezing of soils in autumn and thawing in spring are typical for the tundra, boreal, and temperate soils. The thawing of soils during winter-summer transitions induces the release of decomposable organic carbon and acceleration of soil respiration. The winter-spring fluxes of CO(2 )from permanently and seasonally frozen soils are essential part of annual carbon budget varying from 5 to 50%. The mechanisms of the freeze-thaw activation are not absolutely clear and need clarifying. We investigated the effect of repeated freezing-thawing events on CO(2 )emission from intact arable and forest soils (Luvisols, loamy silt; Central Germany) at different moisture (65% and 100% of WHC). RESULTS: Due to the measurement of the CO(2 )flux in two hours intervals, the dynamics of CO(2 )emission during freezing-thawing events was described in a detailed way. At +10°C (initial level) in soils investigated, carbon dioxide emission varied between 7.4 to 43.8 mg C m(-2)h(-1 )depending on land use and moisture. CO(2 )flux from the totally frozen soil never reached zero and amounted to 5 to 20% of the initial level, indicating that microbial community was still active at -5°C. Significant burst of CO(2 )emission (1.2–1.7-fold increase depending on moisture and land use) was observed during thawing. There was close linear correlation between CO(2 )emission and soil temperature (R(2 )= 0.86–0.97, P < 0.001). CONCLUSION: Our investigations showed that soil moisture and land use governed the initial rate of soil respiration, duration of freezing and thawing of soil, pattern of CO(2 )dynamics and extra CO(2 )fluxes. As a rule, the emissions of CO(2 )induced by freezing-thawing were more significant in dry soils and during the first freezing-thawing cycle (FTC). The acceleration of CO(2 )emission was caused by different processes: the liberation of nutrients upon the soil freezing, biological activity occurring in unfrozen water films, and respiration of cold-adapted microflora
Holographic Entanglement Entropy in Lovelock Gravities
We study entanglement entropies of simply connected surfaces in field
theories dual to Lovelock gravities. We consider Gauss-Bonnet and cubic
Lovelock gravities in detail. In the conformal case the logarithmic terms in
the entanglement entropy are governed by the conformal anomalies of the CFT; we
verify that the holographic calculations are consistent with this property. We
also compute the holographic entanglement entropy of a slab in the Gauss-Bonnet
examples dual to relativistic and non-relativistic CFTs and discuss its
properties. Finally, we discuss features of the entanglement entropy in the
backgrounds dual to renormalization group flows between fixed points and
comment on the implications for a possible c-theorem in four spacetime
dimensions.Comment: harvmac, 30 pages, 1 figure, References added, typos correcte
QCD and strongly coupled gauge theories : challenges and perspectives
We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe