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"Roberts, C"
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Constructing global public goods
Why do international actors provide global public goods when they could free-ride on the production of others? 'Constructing Global Public Goods' examines this question by understanding the identities and preferences of the actors. Most rational choice models of public goods explain the public goods decision by examining the strategic interactions among the actors. They generally avoid the question of how utilities and preferences are formed. 'Constructing Global Public Goods' brings a constructivist approach to the study of public goods by recognizing that the actors' utilities and preferences are socially constructed from the identities the actors take on in the choice situation. The book develops a formal model that links the interpretation of unobserved utilities to preferences for the public goods outcome. It then applies the model to case studies on global monetary management, collective security, and protecting human rights. Bringing constructivism into the public goods decision allows the analysis to look beyond the limited Prisoner's Dilemma based model of most rational choice approaches and recognizes that the decision whether or not to produce a global public good is a complex web of social, political and cultural factors.
Book
Spectrum of fully-heavy tetraquarks from a diquark+antidiquark perspective
Using a relativized diquark model Hamiltonian, we calculate the masses of
J
PC
=
0
+
+
ground-state tetraquarks in the following systems:
b
s
b
¯
s
¯
,
b
b
n
¯
n
¯
(
n
=
u
,
d
),
b
b
s
¯
s
¯
,
c
c
c
¯
c
¯
,
b
b
b
¯
b
¯
,
b
c
b
¯
c
¯
and
b
b
c
¯
c
¯
. We also compute extensive spectra for the fully-heavy quark flavour combinations. Finally, as a test of the diquark model approach, we compute the masses of fully-heavy baryons in the diquark model. Our results may be compared soon to the forthcoming experimental data for fully-heavy three-quark systems.
Journal Article
Kaon and pion parton distributions
Beginning with results for the leading-twist two-particle distribution amplitudes of
π
- and
K
-mesons, each of which exhibits dilation driven by the mechanism responsible for the emergence of hadronic mass, we develop parameter-free predictions for the pointwise behaviour of all
π
and
K
distribution functions (DFs), including glue and sea. The large-
x
behaviour of each DF meets expectations based on quantum chromodynamics; the valence-quark distributions match extractions from available data, including the pion case when threshold resummation effects are included; and at
ζ
5
=
5.2
GeV, the scale of existing measurements, the light-front momentum of these hadrons is shared as follows:
⟨
x
valence
⟩
π
=
0.41
(
4
)
,
⟨
x
glue
⟩
π
=
0.45
(
2
)
,
⟨
x
sea
⟩
π
=
0.14
(
2
)
; and
⟨
x
valence
⟩
K
=
0.42
(
3
)
,
⟨
x
glue
⟩
K
=
0.44
(
2
)
,
⟨
x
sea
⟩
K
=
0.14
(
2
)
. The kaon’s glue and sea distributions are similar to those in the pion, although the inclusion of mass-dependent splitting functions introduces some differences on the valence-quark domain. This study should stimulate improved analyses of existing data and motivate new experiments sensitive to all
π
and
K
DFs. With little known empirically about the structure of the Standard Model’s (pseudo-) Nambu-Goldstone modes and analyses of existing, limited data being controversial, it is likely that new generation experiments at upgraded and anticipated facilities will provide the information needed to resolve the puzzles and complete the picture of these complex bound states.
Journal Article
Impact of ocean resolution and mean state on the rate of AMOC weakening
We examine the weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to increasing CO2 at different horizontal resolutions in a state-of-the-art climate model and in a small ensemble of models with differing resolutions. There is a strong influence of the ocean mean state on the AMOC weakening: models with a more saline western subpolar gyre have a greater formation of deep water there. This makes the AMOC more susceptible to weakening from an increase in CO2 since weakening ocean heat transports weaken the contrast between ocean and atmospheric temperatures and hence weaken the buoyancy loss. In models with a greater proportion of deep water formation further north (in the Greenland-Iceland-Norwegian basin), deep-water formation can be maintained by shifting further north to where there is a greater ocean-atmosphere temperature contrast. We show that ocean horizontal resolution can have an impact on the mean state, and hence AMOC weakening. In the models examined, those with higher resolutions tend to have a more westerly location of the North Atlantic Current and stronger subpolar gyre. This likely leads to a greater impact of the warm, saline subtropical Atlantic waters on the western subpolar gyre resulting in greater dense water formation there. Although there is some improvement of the higher resolution models over the lower resolution models in terms of the mean state, both still have biases and it is not clear which biases are the most important for influencing the AMOC strength and response to increasing CO2.
Journal Article
Six research priorities for cities and climate change
Xuemei Bai and colleagues call for long-term, cross-disciplinary studies to reduce carbon emissions and urban risks from global warming.
Xuemei Bai and colleagues call for long-term, cross-disciplinary studies to reduce carbon emissions and urban risks from global warming.
Journal Article
Safety and Immunogenicity of SARS-CoV-2 mRNA-1273 Vaccine in Older Adults
The Moderna mRNA-1273 vaccine, which elicited antibodies and T cells specific for the Covid-19 virus in adults 55 years of age or younger, elicited similarly high levels of neutralizing-antibody and CD4 T-cell responses in a small group of older adults, including those 71 years of age or older.
Journal Article