184 research outputs found
Null energy condition and superluminal propagation
We study whether a violation of the null energy condition necessarily implies
the presence of instabilities. We prove that this is the case in a large class
of situations, including isotropic solids and fluids relevant for cosmology. On
the other hand we present several counter-examples of consistent effective
field theories possessing a stable background where the null energy condition
is violated. Two necessary features of these counter-examples are the lack of
isotropy of the background and the presence of superluminal modes. We argue
that many of the properties of massive gravity can be understood by associating
it to a solid at the edge of violating the null energy condition. We briefly
analyze the difficulties of mimicking in scalar tensor theories of
gravity.Comment: 46 pages, 6 figure
Atomic Dark Matter
We propose that dark matter is dominantly comprised of atomic bound states.
We build a simple model and map the parameter space that results in the early
universe formation of hydrogen-like dark atoms. We find that atomic dark matter
has interesting implications for cosmology as well as direct detection:
Protohalo formation can be suppressed below for weak scale dark matter due to Ion-Radiation interactions in the
dark sector. Moreover, weak-scale dark atoms can accommodate hyperfine
splittings of order 100 \kev, consistent with the inelastic dark matter
interpretation of the DAMA data while naturally evading direct detection
bounds.Comment: 17 pages, 3 figure
Integrable Spin Chains on the Conformal Moose
We consider N=1, D=4 superconformal U(N)^{pq} Yang-Mills theories dual to
AdS_5xS^5/Z_pxZ_q orbifolds. We construct the dilatation operator of this
superconformal gauge theory at one-loop planar level. We demonstrate that a
specific sector of this dilatation operator can be thought of as the transfer
matrix for a two-dimensional statistical mechanical system, related to an
integrable SU(3) anti-ferromagnetic spin chain system, which in turn is
equivalent to a 2+1-dimensional string theory where the spatial slices are
discretized on a triangular lattice. This is an extension of the SO(6) spin
chain picture of N=4 super Yang-Mills theory. We comment on the integrability
of this N=1 gauge theory and hence the corresponding three-dimensional
statistical mechanical system, its connection to three-dimensional lattice
gauge theories, extensions to six-dimensional string theories, AdS/CFT type
dualities and finally their construction via orbifolds and brane-box models. In
the process we discover a new class of almost-BPS BMN type operators with large
engineering dimensions but controllably small anomalous corrections.Comment: 53 pages, 14 eps figures; Added reference
Nuclear effects in the Drell-Yan process at very high energies
We study Drell-Yan (DY) dilepton production in proton(deuterium)-nucleus and
in nucleus-nucleus collisions within the light-cone color dipole formalism.
This approach is especially suitable for predicting nuclear effects in the DY
cross section for heavy ion collisions, as it provides the impact parameter
dependence of nuclear shadowing and transverse momentum broadening, quantities
that are not available from the standard parton model. For p(D)+A collisions we
calculate nuclear shadowing and investigate nuclear modification of the DY
transverse momentum distribution at RHIC and LHC for kinematics corresponding
to coherence length much longer than the nuclear size. Calculations are
performed separately for transversely and longitudinally polarized DY photons,
and predictions are presented for the dilepton angular distribution.
Furthermore, we calculate nuclear broadening of the mean transverse momentum
squared of DY dileptons as function of the nuclear mass number and energy. We
also predict nuclear effects for the cross section of the DY process in heavy
ion collisions. We found a substantial nuclear shadowing for valence quarks,
stronger than for the sea.Comment: 46 pages, 18 figures, title changed and some discussion added,
accepted for publication in PR
Wavelets techniques for pointwise anti-Holderian irregularity
In this paper, we introduce a notion of weak pointwise Holder regularity,
starting from the de nition of the pointwise anti-Holder irregularity. Using
this concept, a weak spectrum of singularities can be de ned as for the usual
pointwise Holder regularity. We build a class of wavelet series satisfying the
multifractal formalism and thus show the optimality of the upper bound. We also
show that the weak spectrum of singularities is disconnected from the casual
one (denoted here strong spectrum of singularities) by exhibiting a
multifractal function made of Davenport series whose weak spectrum di ers from
the strong one
Critical Reflections on Methodological Challenge in Arts and Dementia Evaluation and Research
Methodological rigour, or its absence, is often a focus of concern for the emerging field of evaluation and research around arts and dementia. However, this paper suggests that critical attention should also be paid to the way in which individual perceptions, hidden assumptions and underlying social and political structures influence methodological work in the field. Such attention will be particularly important for addressing methodological challenges relating to contextual variability, ethics, value judgement, and signification identified through a literature review on this topic. Understanding how, where and when evaluators and researchers experience such challenges may help to identify fruitful approaches for future evaluation.
This paper is based upon a presentation on the subject given at the First International Research Conference on the Arts and Dementia: Theory, Methodology and Evidence on 9 March 2017
Stability and collapse of localized solutions of the controlled three-dimensional Gross-Pitaevskii equation
On the basis of recent investigations, a newly developed analytical procedure
is used for constructing a wide class of localized solutions of the controlled
three-dimensional (3D) Gross-Pitaevskii equation (GPE) that governs the
dynamics of Bose-Einstein condensates (BECs). The controlled 3D GPE is
decomposed into a two-dimensional (2D) linear Schr\"{o}dinger equation and a
one-dimensional (1D) nonlinear Schr\"{o}dinger equation, constrained by a
variational condition for the controlling potential. Then, the above class of
localized solutions are constructed as the product of the solutions of the
transverse and longitudinal equations. On the basis of these exact 3D
analytical solutions, a stability analysis is carried out, focusing our
attention on the physical conditions for having collapsing or non-collapsing
solutions.Comment: 21 pages, 14 figure
Early Sexual Abuse, Street Adversity, and Drug Use among Female Homeless and Runaway Adolescents in the Midwest
Combination of searches for Higgs boson pairs in pp collisions at \sqrts = 13 TeV with the ATLAS detector
This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb(-1) of proton-proton collision data at a centre-of-mass energy root s = 13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the b (b) over barb (b) over bar, b (b) over barW(+)W(-), b (b) over bar tau(+)tau(-), W+W-W+W-, b (b) over bar gamma gamma and W+W-gamma gamma final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (kappa(lambda)) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to -5.0 < kappa(lambda) < 12.0 (-5.8 < kappa(lambda) < 12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model. For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2019.135103</p
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