4,428 research outputs found
Hyper-Scaling Relations in the Conformal Window from Dynamic AdS/QCD
Dynamic AdS/QCD is a holographic model of strongly coupled gauge theories
with the dynamics included through the running anomalous dimension of the quark
bilinear, gamma. We apply it to describe the physics of massive quarks in the
conformal window of SU(N_c) gauge theories with N_f fundamental flavours,
assuming the perturbative two loop running for gamma. We show that to find
regular, holographic, renormalization group flows in the infra-red the
decoupling of the quark flavours at the scale of the mass is important and
enact it through suitable boundary conditions when the flavours become on
shell. We can then compute the quark condensate and the mesonic spectrum
(M_rho, M_pi, M_sigma) and decay constants. We compute their scaling dependence
on the quark mass for a number of examples. The model matches perturbative
expectations for large quark mass and naive dimensional analysis (including the
anomalous dimensions) for small quark mass. The model allows study of the
intermediate regime where there is an additional scale from the running of the
coupling and we present results for the deviation of scalings from assuming
only the single scale of the mass.Comment: 12 pages, 26 figures, new references adde
Propane from the North Slope: Could It Reduce Energy Costs in the Interior?
Could propane from the North Slope cut energy costs in Fairbanks and
other Interior communities that heat buildings or generate electricity
with fuel oil or naphtha? The Alaska Natural Gas Development Authority
(ANGDA) thinks it could.
That’s because a North Slope producer has agreed to sell ANGDA
propane for considerably less than what it might otherwise cost, if there
were a natural gas pipeline. Propane is a component of North Slope natural
gas—and right now there’s no way to get that gas to market.*
Naphtha and fuel oil, by comparison, are refined from oil—so their
prices are closely tied to the volatile price of crude oil. ANGDA hopes getting
a price break on propane could make it cheaper, at least until a pipeline
is built—and it asked ISER to analyze the potential effects of one idea.Alaska Natural Gas Development Authorit
Inverse Magnetic Catalysis in Bottom-Up Holographic QCD
We explore the effect of magnetic field on chiral condensation in QCD via a
simple bottom up holographic model which inputs QCD dynamics through the
running of the anomalous dimension of the quark bilinear. Bottom up holography
is a form of effective field theory and we use it to explore the dependence on
the coefficients of the two lowest order terms linking the magnetic field and
the quark condensate. In the massless theory, we identify a region of parameter
space where magnetic catalysis occurs at zero temperature but inverse magnetic
catalysis at temperatures of order the thermal phase transition. The model
shows similar non-monotonic behaviour in the condensate with B at intermediate
T as the lattice data. This behaviour is due to the separation of the meson
melting and chiral transitions in the holographic framework. The introduction
of quark mass raises the scale of B where inverse catalysis takes over from
catalysis until the inverse catalysis lies outside the regime of validity of
the effective description leaving just catalysis.Comment: 9 pages, 8 figure
Translational Symmetry Breaking in Higgs & Gauge Theory, and the Cosmological Constant
We argue, at a very basic effective field theory level, that higher dimension
operators in scalar theories that break symmetries at scales close to their
ultraviolet completion cutoff, include terms that favour the breaking of
translation (Lorentz) invariance, potentially resulting in striped, chequered
board or general crystal-like phases. Such descriptions can be thought of as
the effective low energy description of QCD-like gauge theories near their
strong coupling scale where terms involving higher dimension operators are
generated. Our low energy theory consists of scalar fields describing operators
such as and . Such scalars can have kinetic
mixing terms that generate effective momentum dependent contributions to the
mass matrix. We show that these can destabilize the translationally invariant
vacuum. It is possible that in some real gauge theory such operators could
become sufficiently dominant to realize such phases and it would be interesting
to look for them in lattice simulations. We present a holographic model of the
same phenomena which includes RG running. A key phenomenological motive to look
at such states is recent work that shows that the non-linear response in
gravity to such short range fluctuations can mimic a cosmological constant.
Intriguingly in a cosmology with such a Starobinsky inflation term, to generate
the observed value of the present day acceleration would require stripes at the
electroweak scale. Unfortunately, low energy phenomenological constraints on
Lorentz violation in the electron-photon system appear to strongly rule out any
such possibility outside of a disconnected dark sector.Comment: 9 pages, 1 figure; minor changes. Version to be published in PR
Altmetrics are the central way of measuring communication in the digital age but what do they miss?
Inspired by the push towards altmetrics, Nick Scott sees great potential to better communicate indicators of academic success. But this does constitute impact? Here, he puts forward questions on media mentions, website page hits and the ‘dark stuff’
Entangled granular media
We study the geometrically induced cohesion of ensembles of granular
"u-particles" which mechanically entangle through particle interpenetration. We
vary the length-to-width ratio of the u-particles and form them into
free-standing vertical columns. In laboratory experiment we monitor the
response of the columns to sinusoidal vibration (frequency , peak
acceleration ). Column collapse occurs in a characteristic time,
, which follows the relation .
resembles an activation energy and is maximal at intermediate .
Simulation reveals that optimal strength results from competition between
packing and entanglement.Comment: 4 pages, 5 figure
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