8,760 research outputs found
Comment: The Essential Role of Pair Matching
Comment on "The Essential Role of Pair Matching in Cluster-Randomized
Experiments, with Application to the Mexican Universal Health Insurance
Evaluation" [arXiv:0910.3752]Comment: Published in at http://dx.doi.org/10.1214/09-STS274A the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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
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
The Right Time and Proper Measure: Assessing In Writing Centers and James Kinneavy's "Kairos: A Neglected Concept in Classical Rhetoric."
In my experience working with tutors and college
student writers over the last nine years, I am frequently
reminded how important kairos is to my work. For
example, a tutoring approach that might help Renee
with her annotated bibliography draft won’t
necessarily help Kevin understand his research essay
prompt. The difference lies not in the fact that they
are writing different essays; rather, each writer presents
a different rhetorical situation with unique audiences,
circumstances, exigencies, and contexts. Even if both
students were writing the exact same essay on the
exact same topic, their experience, confidence, and
attitude toward writing would present different
opportunities in a tutoring session. Although patterns
exist and I begin and close a session in routine ways, I
am frequently reminded by crossed arms, furrowed
brows, and deep sighs that a tutoring approach
ignoring kairos results in little learning and growth for
the student as a writer and me as a tutor. The
relevance of the term to writing center work can also
be witnessed in an administrative sense. For example,
interrupting a session to suggest a different approach
for a tutor might be helpful; however, I may be more
persuasive if I more carefully choose a time to provide
feedback on a consultation.University Writing Cente
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