7,701 research outputs found
Mutually cooperative epidemics on power-law networks
The spread of an infectious disease can, in some cases, promote the
propagation of other pathogens favouring violent outbreaks, which cause a
discontinuous transition to an endemic state. The topology of the contact
network plays a crucial role in these cooperative dynamics. We consider a
susceptible--infected--removed (SIR) type model with two mutually cooperative
pathogens: an individual already infected with one disease has an increased
probability of getting infected by the other. We present an heterogeneous
mean-field theoretical approach to the co--infection dynamics on generic
uncorrelated power-law degree-distributed networks and validate its results by
means of numerical simulations. We show that, when the second moment of the
degree distribution is finite, the epidemic transition is continuous for low
cooperativity, while it is discontinuous when cooperativity is sufficiently
high. For scale-free networks, i.e. topologies with diverging second moment,
the transition is instead always continuous. In this way we clarify the effect
of heterogeneity and system size on the nature of the transition and we
validate the physical interpretation about the origin of the discontinuity.Comment: 9 pages, 5 figure
Effect of network clustering on mutually cooperative coinfections
The spread of an infectious disease can be promoted by previous infections
with other pathogens. This cooperative effect can give rise to violent
outbreaks, reflecting the presence of an abrupt epidemic transition. As for
other diffusive dynamics, the topology of the interaction pattern of the host
population plays a crucial role. It was conjectured that a discontinuous
transition arises when there are relatively few short loops and many long loops
in the contact network. Here we focus on the role of local clustering in
determining the nature of the transition. We consider two mutually cooperative
pathogens diffusing in the same population: an individual already infected with
one disease has an increased probability of getting infected by the other. We
look at how a disease obeying the susceptible-infected-removed dynamics spreads
on contact networks with tunable clustering. Using numerical simulations we
show that for large cooperativity the epidemic transition is always abrupt,
with the discontinuity decreasing as clustering is increased. For large
clustering strong finite size effects are present and the discontinuous nature
of the transition is manifest only in large networks. We also investigate the
problem of influential spreaders for cooperative infections, revealing that
both cooperativity and clustering strongly enhance the dependence of the
spreading influence on the degree of the initial seed.Comment: 8 pages, 8 figure
Epidemic spreading dynamics with drug-resistant and heterogeneous contacts
Drug resistance and strong contacts actually play crucial roles in epidemic
spread in complex systems. Nevertheless, neither theoretical model or
methodology is proposed to address this. We thus consider an edge-based
epidemic spread model considering the two key ingredients, in which the
contacts are grouped into two classes: strong contacts and normal ones. Next,
we present a unified edge-based compartmental approach to the spread dynamics
on Erd\"{o}s-R\'{e}nyi (ER) networks and validate its results by extensive
numerical simulations. In case that epidemic is totally drug-resistant, we both
numerically and theoretically show a slow outbreak (continuous transition) of
epidemics when number of strong contacts is not enough for the emergence of
null threshold. If the epidemic owns partial resistance, we would observe
evident faster-growing outbreaks (discontinuous transitions) and larger final
epidemic sizes for few strong contacts, instead of emergence of null threshold
with increase of strong contacts. Inhibiting effect of infection threshold,
positive roles of strong contacts and strength of strong contacts in promoting
outbreaks are also approved. Throughout this paper, we could drive exact
predictions through the analytical approach, showing good agreements with
numerical simulations
Discriminating Local Sources of High-Energy Cosmic Electrons and Positrons by Current and Future Anisotropy Measurements
The Fermi-LAT detects no significant anisotropy of the cosmic-ray (CR)
electrons and positrons () with seven years of data, which provides
the strongest restriction to the anisotropy up to now. As next
generation CR observatory, HERD is expected to have a better capability of
anisotropy detection than Fermi-LAT. In this paper, we discuss several models
aimed to explain the AMS-02 data by the present and future anisotropy
measurements. We find that the upper limits of Fermi-LAT disfavor Vela SNR as
the dominant source in sub-TeV, while other cases that remain safe under the
constraint of Fermi-LAT are expected to be distinguished from each other by
HERD. We then discuss the possibilities of remarkable TeV spectral features,
and test the corresponding anisotropies. We find the conditions under which the
TeV model can have a prominent spectral feature and avoid the constraint of
Fermi-LAT at the same time. Furthermore, the expected performance of HERD is
sensitive enough to detect the anisotropies of all these TeV models, and even
for the case of a featureless TeV spectrum. Thus HERD may play a crucial part
in the study of the origin of cosmic electrons and positrons.Comment: 12 pages, 8 figures, 4 tables, accepted for publication in MNRA
Status of Dark Matter Detection
The detection of dark matter has made great progresses in recent years. We
give a brief review on the status and progress in dark matter detection,
including the progresses in direct detection, collider detection at LHC and
focus on the indirect detection. The results from PAMELA, ATIC, Fermi-LAT and
relevant studies on these results are introduced. Then we give the progress on
indirect detection of gamma rays from Fermi-LAT and ground based Cerenkov
telescopes. Finally the detection of neutrinos and constraints on the nature of
dark matter are reviewed briefly.Comment: 33 pages, invited revie
Small world yields optimal public goods in presence of both altruistic and selfish cooperators
Empirical studies have shown that individuals' behaviors are largely
influenced by social conformity, including punishment. However, a
coevolutionary theoretical framework that takes into account effects of
conformity on individuals' punishment behaviors has not been put forward yet.
Herein we propose a coevolutionary game model to extend the theory of
cooperation with conformity in spatial public goods game by considering pool
punishment, as well as two converse feedback modes of conformity that strongly
affect cooperators' punishment behaviors. We focus on how different parameters
and spatial structures govern evolutionary dynamics on three different kinds of
networks by employing mean-field analysis based on replicator dynamics and
Monte Carlo simulations. On regular lattices, defectors are overall extincted
since cooperators, especially selfish cooperators, have great evolutionary
advantages due to strong network reciprocity, and at the same time the number
of altruistic cooperators decays. Conversely, abundant shortcuts in regular
random networks lead to the prevalence of altruistic cooperators, but
cooperators suffer from free-riding behaviors of defectors. Of particular
interest, we find that small-world topology can simultaneously help cooperators
successfully outperform defectors by means of strong network reciprocity, and
enable rich contacting opportunities with defectors to facilitate the expansion
of altruistic cooperators. Therefore, we clarify that small world is the
optimal topology subject to the dominance of altruistic cooperators.Comment: 12 pages 14 figure
Explanation of the knee-like feature in the DAMPE cosmic energy spectrum
The DArk Matter Particle Explorer (DAMPE), a space-based high precision
cosmic ray detector, has just reported the new measurement of the total
electron plus positron energy spectrum up to 4.6 TeV. A notable feature in the
spectrum is the spectral break at TeV, with the spectral index
softening from to . Such a feature is very similar to the knee at
the cosmic nuclei energy spectrum. In this work we propose that the knee-like
feature can be explained naturally by assuming that the electrons are
accelerated at the supernova remnants (SNRs) and released when the SNRs die out
with lifetime around years. The cut-off energy of those electrons have
already decreased to several TeV due to radiative cooling, which may induce the
observed TeV spectral break. Another possibility is that the break is induced
by a single nearby old SNR. Such a scenario may bring a large electron flux
anisotropy that is observable by the future detectors. We also show that a
minor part of electrons escaping during the acceleration in young and nearby
SNRs are able to contribute to several TeV or higher energy region of the
spectrum.Comment: 23 pages, 4 figures, 2 table
Possible origin of the slow-diffusion region around Geminga
Geminga pulsar is surrounded by a multi-TeV -ray halo radiated by the
high energy electrons and positrons accelerated by the central pulsar wind
nebula (PWN). The angular profile of the -ray emission reported by HAWC
indicates an anomalously slow diffusion for the cosmic-ray electrons and
positrons in the halo region around Geminga. In the paper we study the possible
mechanism for the origin of the slow diffusion. At first, we consider the
self-generated Alfv\'en waves due to the streaming instability of the electrons
and positrons released by Geminga. However, even considering a very optimistic
scenario for the wave growth, we find this mechanism DOES NOT work to account
for the extremely slow diffusion at the present day if taking the proper motion
of Geminga pulsar into account. The reason is straightforward as the PWN is too
weak to generate enough high energy electrons and positrons to stimulate strong
turbulence at the late time. We then propose an assumption that the strong
turbulence is generated by the shock wave of the parent supernova remnant (SNR)
of Geminga. Geminga may still be inside the SNR, and we find that the SNR can
provide enough energy to generate the slow-diffusion circumstance. The TeV
halos around PSR B0656+14, Vela X, and PSR J1826-1334 may also be explained
under this assumption.Comment: 7 pages, 5 figures, accepted by MNRA
Probing Light Stop Pairs at the LHC
In this work, we study the light stop pair signals at the LHC. We explore the
SUSY parameter space with non-universal gaugino and third generation masses at
the GUT scale. Recent LHC SUSY search results based on 35pb and
1fb of data are implemented to put the limits on stop pair events. The
dark matter relic density and direct detection constraints are also taken into
account. Detailed simulations on the signals and background for some benchmark
points are performed, and it is found that the stop pair signals usually escape
the LHC search if the present cut conditions are used. We also explore the
potential and sensitivity of ILC to probe such scenarios. It is found that the
ILC can detect them with an integrated luminosity of a few tens of fb.Comment: 35pages, 13figure
Expectations of the Cosmic Antideuteron Flux
The cosmic antideuteron is a promising probe for the dark matter annihilation
signature. In order to determine the DM signature, the background astrophysical
antideuteron flux should be carefully studied. In this work we provide a new
calculation of the secondary antideuteron flux, and pay special attention to
the uncertainties from hadronic interaction models by using several Monte Carlo
generators. The uncertainties from propagation effects are also carefully
investigated for both the astrophysical background and DM annihilation
signature in several scenarios, which are constrained by the latest B/C ratio
measured by AMS-02. Considering these uncertainties, we find that the secondary
antideuteron flux is hard to detect in the near future detectors. However, the
antideuteron signature from dark matter annihilation will be detectable even
considering the constraint from the AMS-02 observation of the
ratio.Comment: 22 pages, 9 figure
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