29,008 research outputs found
The topologically twisted index of super-Yang-Mills on and the elliptic genus
We examine the topologically twisted index of super-Yang-Mills
with gauge group on , and demonstrate that it receives
contributions from multiple sectors corresponding to the freely acting
orbifolds where . After summing over
these sectors, the index can be expressed as the elliptic genus of a
two-dimensional theory resulting from Kaluza-Klein reduction
on . This provides an alternate path to the 'high-temperature' limit of
the index, and confirms the connection to the right-moving central charge of
the theory.Comment: 29 pages, 1 figure; v2: restricted to real chemical potentials in
section 4 and added a comment on the index where in
section
A controlled expansion for certain non-Fermi liquid metals
The destruction of Fermi liquid behavior when a gapless Fermi surface is
coupled to a fluctuating gapless boson field is studied theoretically. This
problem arises in a number of different contexts in quantum many body physics.
Examples include fermions coupled to a fluctuating transverse gauge field
pertinent to quantum spin liquid Mott insulators, and quantum critical metals
near a Pomeranchuk transition. We develop a new controlled theoretical approach
to determining the low energy physics. Our approach relies on combining an
expansion in the inverse number (N) of fermion species with a further expansion
in the parameter \epsilon = z_b -2 where z_b is the dynamical critical exponent
of the boson field. We show how this limit allows a systematic calculation of
the universal low energy physics of these problems. The method is illustrated
by studying spinon fermi surface spin liquids, and a quantum critical metal at
a second order electronic nematic phase transition. We calculate the low energy
single particle spectra, and various interesting two particle correlation
functions. In some cases deviations from the popular Random Phase Approximation
results are found. Some of the same universal singularities are also calculated
to leading non-vanishing order using a perturbative renormalization group
calculation at small N extending previous results of Nayak and Wilczek.
Implications for quantum spin liquids, and for Pomeranchuk transitions are
discussed. For quantum critical metals at a nematic transition we show that the
tunneling density of states has a power law suppression at low energies.Comment: 19 pages, 15 figure
Subleading corrections to the free energy of necklace quiver theories dual to massive IIA
We investigate the free energy of Chern-Simons-matter
quiver gauge theories with gauge group where the sum of
Chern-Simons levels does not vanish, beyond the leading order in the large-
expansion. We take two different approaches to explore the sub-leading
structures of the free energy. First we evaluate the matrix integral for the
partition function in the 't~Hooft limit using a saddle point approximation.
Second we use an ideal Fermi-gas model to compute the same partition function,
but in the limit of fixed Chern-Simons levels. The resulting expressions for
the free energy are consistent with each other at the leading and
first sub-leading order. The Fermi-gas approach also hints at a universal
correction to the free energy. Since the quiver gauge
theories we consider are dual to massive Type IIA theory, we expect our results
to match sub-leading corrections to the holographic dual free energy, which
have not yet been fully investigated.Comment: v1: 50 pages, 1figure; v2: minor revision
New Method for Numerically Solving the Chemical Potential Dependence of the Dressed Quark Propagator
Based on the rainbow approximation of Dyson-Schwinger equation and the
assumption that the inverse dressed quark propagator at finite chemical
potential is analytic in the neighborhood of , a new method for
obtaining the dressed quark propagator at finite chemical potential from
the one at zero chemical potential is developed. Using this method the dressed
quark propagator at finite chemical potential can be obtained directly from the
one at zero chemical potential without the necessity of numerically solving the
corresponding coupled integral equations by iteration methods. A comparison
with previous results is given.Comment: Revtex, 14 pages, 5 figure
On the Origins and Control of Community Types in the Human Microbiome
Microbiome-based stratification of healthy individuals into compositional
categories, referred to as "community types", holds promise for drastically
improving personalized medicine. Despite this potential, the existence of
community types and the degree of their distinctness have been highly debated.
Here we adopted a dynamic systems approach and found that heterogeneity in the
interspecific interactions or the presence of strongly interacting species is
sufficient to explain community types, independent of the topology of the
underlying ecological network. By controlling the presence or absence of these
strongly interacting species we can steer the microbial ecosystem to any
desired community type. This open-loop control strategy still holds even when
the community types are not distinct but appear as dense regions within a
continuous gradient. This finding can be used to develop viable therapeutic
strategies for shifting the microbial composition to a healthy configurationComment: Main Text, Figures, Methods, Supplementary Figures, and Supplementary
Tex
Generational dependency and elderly care : a psychological interpretation of cultural norms and exchange
ln spite of the complexity of such dynamic relationships in the caregiving system, the literature shows that dominant research paradigm has places elderly care in the framework of a simple, unqualified social exchange theory. The primary goal of this paper to critique research approach based on the social exchange theory. First, we wish to discuss how the exchange theory lies at the heart of the debate between the proponents and opponents of having family members as the primary care providers for elderly. We wish to review the basic assumptions that social exchange theory holds about caregiving relationships. Second, we suggest that focusing on the perceptions and expectations between the elderly person and his/her caretaker may instead be a more valuable approach to understanding the caregiving relationship. Here we submit that an example of the perception-expectation approach is reflected in the “secondary baby talk” between caregiver and the elderly. Third, we wish to discuss how such an approach may provide insight into a range of culturally variant behaviors for family members who are caring for elderly
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