1,080 research outputs found
Monojet versus rest of the world I: t-channel Models
Monojet searches using Effective Field Theory (EFT) operators are usually
interpreted as a robust and model independent constraint on direct detection
(DD) scattering cross-sections. At the same time, a mediator particle must be
present to produce the dark matter (DM) at the LHC. This mediator particle may
be produced on shell, so that direct searches for the mediating particle can
constrain the effective operator being applied to monojet constraints. In this
first paper, we do a case study on t-channel models in monojet searches, where
the (Standard Model singlet) DM is pair produced via a t-channel mediating
particle, whose supersymmetric analogue is the squark. We compare monojet
constraints to direct constraints on single or pair production of the mediator
from multi-jets plus missing energy searches and we identify the regions where
the latter dominate over the former. We show that computing bounds using
supersymmetric simplified models and in the narrow width approximation, as done
in previous work in the literature, misses important quantitative effects. We
perform a full event simulation and statistical analysis, and we compute the
effects of both on- and off-shell production of the mediating particle, showing
that for both the monojet and multi-jets plus missing energy searches,
previously derived bounds provided more conservative bounds than what can be
extracted by including all relevant processes in the simulation. Monojets and
searches for supersymmetry (SUSY) provide comparable bounds on a wide range of
the parameter space, with SUSY searches usually providing stronger bounds,
except in the regions where the DM particle and the mediator are very mass
degenerate. The EFT approximation rarely is able to reproduce the actual
limits. In a second paper to follow, we consider the case of s-channel
mediators.Comment: 22 pages + appendices, 10 figure
The fitting of multifunctions : an approach to nonparametric multimodal regression.
In the last decades a lot of research has been devoted to
smoothing in the sense of nonparametric regression. However, this
work has nearly exclusively concentrated on fitting regression
functions. When the conditional distribution of y|x is
multimodal, the assumption of a functional relationship y = m(x)
+ noise might be too restrictive. We introduce a nonparametric
approach to fit multifunctions, allowing to assign a set of
output values to a given x. The concept is based on
conditional mean shift, which is an easily implemented tool to
detect the local maxima of a conditional density function. The
methodology is illustrated by environmental data examples
Central Charge Bounds in 4D Conformal Field Theory
We derive model-independent lower bounds on the stress tensor central charge
C_T in terms of the operator content of a 4-dimensional Conformal Field Theory.
More precisely, C_T is bounded from below by a universal function of the
dimensions of the lowest and second-lowest scalars present in the CFT. The
method uses the crossing symmetry constraint of the 4-point function, analyzed
by means of the conformal block decomposition.Comment: 16 pages, 6 figure
Kinetic energy of a trapped Fermi gas interacting with a Bose-Einstein condensate
We study a confined mixture of bosons and fermions in the regime of quantal
degeneracy, with particular attention to the effects of the interactions on the
kinetic energy of the fermionic component. We are able to explore a wide region
of system parameters by identifying two scaling variables which completely
determine its state at low temperature. These are the ratio of the
boson-fermion and boson-boson interaction strengths and the ratio of the radii
of the two clouds. We find that the effect of the interactions can be sizeable
for reasonable choices of the parameters and that its experimental study can be
used to infer the sign of the boson-fermion scattering length. The interplay
between interactions and thermal effects in the fermionic kinetic energy is
also discussed.Comment: REVTEX, 8 pages, 6 figures included. Small corrections to text and
figures, accepted for publication in EPJ
Temperature-dependent density profiles of trapped boson-fermion mixtures
We present a semiclassical three-fluid model for a Bose-condensed mixture of
interacting Bose and Fermi gases confined in harmonic traps at finite
temperature. The model is used to characterize the experimentally relevant
behaviour of the equilibrium density profile of the fermions with varying
composition and temperature across the onset of degeneracy, for coupling
strengths relevant to a mixture of
K and K atoms.Comment: 9 pages, 2 postscript figures, accepted for publication in Eur. Phys.
Jour.
One-loop adjoint masses for branes at non-supersymmetric angles
This proceeding is based on arXiv:1105.0591 [hep-th] where we consider
breaking of supersymmetry in intersecting D-brane configurations by slight
deviation of the angles from their supersymmetric values. We compute the masses
generated by radiative corrections for the adjoint scalars on the brane
world-volumes. In the open string channel, the string two-point function
receives contributions only from the infrared limits of N~4 and N~2
supersymmetric configurations, via messengers and their Kaluza-Klein
excitations, and leads at leading order to tachyonic directions.Comment: 15 pages, 5 figures. Contribution to the proceedings of the Corfu
Summer Institute 2011 School and Workshops on Elementary Particle Physics and
Gravity, September 4-18 2011 Corfu, Greec
Skill assessment of the PELAGOS global ocean biogeochemistry model over the period 1980–2000
Global Ocean Biogeochemistry General Circulation Models are useful tools to study biogeochemical processes at global and large scales under current climate and future scenario conditions. The credibility of future estimates is however dependent on the model skill in capturing the observed multi-annual variability of firstly the mean bulk biogeochemical properties, and secondly the rates at which organic matter is processed within the food web. For this double purpose, the results of a multi-annual simulation of the global ocean biogeochemical model PELAGOS have been objectively compared with multi-variate observations from the last 20 years of the 20th century, both considering bulk variables and carbon production/consumption rates. Simulated net primary production (NPP) is comparable with satellite-derived estimates at the global scale and when compared with an independent data-set of in situ observations in the equatorial Pacific. The usage of objective skill indicators allowed us to demonstrate the importance of comparing like with like when considering carbon transformation processes. NPP scores improve substantially when in situ data are compared with modeled NPP which takes into account the excretion of freshly-produced dissolved organic carbon (DOC). It is thus recommended that DOC measurements be performed during in situ NPP measurements to quantify the actual production of organic carbon in the surface ocean. The chlorophyll bias in the Southern Ocean that affects this model as well as several others is linked to the inadequate representation of the mixed layer seasonal cycle in the region. A sensitivity experiment confirms that the artificial increase of mixed layer depths towards the observed values substantially reduces the bias. Our assessment results qualify the model for studies of carbon transformation in the surface ocean and metabolic balances. Within the limits of the model assumption and known biases, PELAGOS indicates a net heterotrophic balance especially in the more oligotrophic regions of the Atlantic during the boreal winter period. However, at the annual time scale and over the global ocean, the model suggests that the surface ocean is close to a weakly positive autotrophic balance in accordance with recent experimental findings and geochemical considerations
BFM-SI: A new implementation of the biogeochemical flux model in sea ice
This work describes a novel implementation of the Biogeochemical Flux Model (BFM) in a sea ice system (BFMSI). The chosen representative groups of the sea ice food web rely on the same dynamics as the BFM. The main differences between BFM and BFMSI stand in the type and number of functional groups, in the parameters assigned to several physiological and ecological processes and in the dimensional size classes they represent. The differential equations of BFMSI are written here according to the nomenclature associated to the new sea ice state variables. At the boundaries, the sea ice system is also coupled to the atmosphere and to the ocean through the exchange of organic and inorganic matter. This is done by computing the entrapment of particulate and dissolved matter and gases when sea ice grows and release to the ocean when sea ice melts to ensure mass conservation. The implementation of the BFM in sea ice and the coupling structure in General Circulation Models will add a new component that may provide new adequate estimate of the role and importance of sea ice biogeochemistry in the global carbon cycle
Conformal Field Theories in Fractional Dimensions
We study the conformal bootstrap in fractional space-time dimensions,
obtaining rigorous bounds on operator dimensions. Our results show strong
evidence that there is a family of unitary CFTs connecting the 2D Ising model,
the 3D Ising model, and the free scalar theory in 4D. We give numerical
predictions for the leading operator dimensions and central charge in this
family at different values of D and compare these to calculations of phi^4
theory in the epsilon-expansion.Comment: 11 pages, 4 figures - references updated - one affiliation modifie
A process-oriented model study of equatorial Pacific phytoplankton: the role of iron supply and tropical instability waves
The response of phytoplankton growth to iron supply and its modulation by large-scale circulation and tropical instability waves (TIWs) in the eastern equatorial Pacific has been investigated with an ocean biogeochemical model. This process study shows that iron can be efficiently advected from the New Guinea shelf through the Equatorial Undercurrent (EUC) to the eastern Pacific. The presence of a continental iron source is necessary for the maintenance of the observed subsurface iron maximum in the EUC core. In the eastern Pacific region, phytoplankton production is enhanced when additional iron is available in the EUC. Simulated phytoplankton variability is linked to TIWs activity, as revealed by a wavelet analysis of the total autotrophic carbon. The net local effect of the waves on phytoplankton can be either positive or negative depending on several factors. When the iron nutricline is sufficiently shallow to be reached by the wave vertical scale, the effect of the waves is to enhance iron availability in the euphotic zone leading to a net local increase of phytoplankton biomass. We therefore suggest that the local maxima of phytoplankton observed in moorings off the Equator in the eastern Pacific might be not only the result of concentration mechanisms, but also the result of an increase in local production sustained by advected iron
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