301 research outputs found
Parity Doubling and the S Parameter Below the Conformal Window
We describe a lattice simulation of the masses and decay constants of the
lowest-lying vector and axial resonances, and the electroweak S parameter, in
an SU(3) gauge theory with and 6 fermions in the fundamental
representation. The spectrum becomes more parity doubled and the S parameter
per electroweak doublet decreases when is increased from 2 to 6,
motivating study of these trends as is increased further, toward the
critical value for transition from confinement to infrared conformality.Comment: 4 pages, 5 figures; to be submitted to PR
On Glauber modes in Soft-Collinear Effective Theory
Gluon interactions involving spectator partons in collisions at hadronic
machines are investigated. We find a class of examples in which a mode, called
Glauber gluons, must be introduced to the effective theory for consistency.Comment: 19 pages, three figures. Uses JHEP3.cl
Stealth dark matter confinement transition and gravitational waves
We use non-perturbative lattice calculations to investigate the finite-temperature confinement transition of stealth dark matter, focusing on the regime in which this early-universe transition is first order and would generate a stochastic background of gravitational waves. Stealth dark matter extends the standard model with a new strongly coupled SU(4) gauge sector with four massive fermions in the fundamental representation, producing a stable spin-0 'dark baryon' as a viable composite dark matter candidate. Future searches for stochastic gravitational waves will provide a new way to discover or constrain stealth dark matter, in addition to previously investigated direct-detection and collider experiments. As a first step to enabling this phenomenology, we determine how heavy the dark fermions need to be in order to produce a first-order stealth dark matter confinement transition
An effective theory for jet propagation in dense QCD matter: jet broadening and medium-induced bremsstrahlung
Two effects, jet broadening and gluon bremsstrahlung induced by the
propagation of a highly energetic quark in dense QCD matter, are reconsidered
from effective theory point of view. We modify the standard Soft Collinear
Effective Theory (SCET) Lagrangian to include Glauber modes, which are needed
to implement the interactions between the medium and the collinear fields. We
derive the Feynman rules for this Lagrangian and show that it is invariant
under soft and collinear gauge transformations. We find that the newly
constructed theory SCET recovers exactly the general result for the
transverse momentum broadening of jets. In the limit where the radiated gluons
are significantly less energetic than the parent quark, we obtain a jet
energy-loss kernel identical to the one discussed in the reaction operator
approach to parton propagation in matter. In the framework of SCET we
present results for the fully-differential bremsstrahlung spectrum for both the
incoherent and the Landau-Pomeranchunk-Migdal suppressed regimes beyond the
soft-gluon approximation. Gauge invariance of the physics results is
demonstrated explicitly by performing the calculations in both the light-cone
and covariant gauges. We also show how the process-dependent
medium-induced radiative corrections factorize from the jet production cross
section on the example of the quark jets considered here.Comment: 52 pages, 15 pdf figures, as published in JHE
A Quantitative Metric to Identify Critical Elements within Seafood Supply Networks
A theoretical basis is required for comparing key features and critical elements in wild fisheries and aquaculture
supply chains under a changing climate. Here we develop a new quantitative metric that is analogous to indices used to
analyse food-webs and identify key species. The Supply Chain Index (SCI) identifies critical elements as those elements with
large throughput rates, as well as greater connectivity. The sum of the scores for a supply chain provides a single metric that
roughly captures both the resilience and connectedness of a supply chain. Standardised scores can facilitate crosscomparisons
both under current conditions as well as under a changing climate. Identification of key elements along the
supply chain may assist in informing adaptation strategies to reduce anticipated future risks posed by climate change. The
SCI also provides information on the relative stability of different supply chains based on whether there is a fairly even
spread in the individual scores of the top few key elements, compared with a more critical dependence on a few key
individual supply chain elements. We use as a case study the Australian southern rock lobster Jasus edwardsii fishery, which
is challenged by a number of climate change drivers such as impacts on recruitment and growth due to changes in largescale
and local oceanographic features. The SCI identifies airports, processors and Chinese consumers as the key elements in
the lobster supply chain that merit attention to enhance stability and potentially enable growth. We also apply the index to
an additional four real-world Australian commercial fishery and two aquaculture industry supply chains to highlight the
utility of a systematic method for describing supply chains. Overall, our simple methodological approach to empiricallybased
supply chain research provides an objective method for comparing the resilience of supply chains and highlighting
components that may be critical
Fully-Unintegrated Parton Distribution and Fragmentation Functions at Perturbative k_T
We define and study the properties of generalized beam functions (BFs) and
fragmenting jet functions (FJFs), which are fully-unintegrated parton
distribution functions (PDFs) and fragmentation functions (FFs) for
perturbative k_T. We calculate at one loop the coefficients for matching them
onto standard PDFs and FFs, correcting previous results for the BFs in the
literature. Technical subtleties when measuring transverse momentum in
dimensional regularization are clarified, and this enables us to renormalize in
momentum space. Generalized BFs describe the distribution in the full
four-momentum k_mu of a colliding parton taken out of an initial-state hadron,
and therefore characterize the collinear initial-state radiation. We illustrate
their importance through a factorization theorem for pp -> l^+ l^- + 0 jets,
where the transverse momentum of the lepton pair is measured. Generalized FJFs
are relevant for the analysis of semi-inclusive processes where the full
momentum of a hadron, fragmenting from a jet with constrained invariant mass,
is measured. Their significance is shown for the example of e^+ e^- -> dijet+h,
where the perpendicular momentum of the fragmenting hadron with respect to the
thrust axis is measured.Comment: Journal versio
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