1,029 research outputs found
Renormalization of dimension-six operators relevant for the Higgs decays
The discovery of the Higgs boson has opened a new window to test the SM
through the measurements of its couplings. Of particular interest is the
measured Higgs coupling to photons which arises in the SM at the one-loop
level, and can then be significantly affected by new physics. We calculate the
one-loop renormalization of the dimension-six operators relevant for
, which can be potentially important since
it could, in principle, give log-enhanced contributions from operator mixing.
We find however that there is no mixing from any current-current operator that
could lead to this log-enhanced effect. We show how the right choice of
operator basis can make this calculation simple. We then conclude that
can only be affected by RG mixing from
operators whose Wilson coefficients are expected to be of one-loop size, among
them fermion dipole-moment operators which we have also included.Comment: 21 pages. Improved version with h -> gamma Z results added and
structure of anomalous-dimension matrix determined further. Conclusions
unchange
Nonlinear optics of fibre event horizons
The nonlinear interaction of light in an optical fibre can mimic the physics
at an event horizon. This analogue arises when a weak probe wave is unable to
pass through an intense soliton, despite propagating at a different velocity.
To date, these dynamics have been described in the time domain in terms of a
soliton-induced refractive index barrier that modifies the velocity of the
probe. Here, we complete the physical description of fibre-optic event horizons
by presenting a full frequency-domain description in terms of cascaded
four-wave mixing between discrete single-frequency fields, and experimentally
demonstrate signature frequency shifts using continuous wave lasers. Our
description is confirmed by the remarkable agreement with experiments performed
in the continuum limit, reached using ultrafast lasers. We anticipate that
clarifying the description of fibre event horizons will significantly impact on
the description of horizon dynamics and soliton interactions in photonics and
other systems.Comment: 7 pages, 5 figure
Performance evaluation of a multi-user virtual reality platform
Virtual Reality (VR) popularity is increasing as it is becoming more affordable for end users. Available VR hardware includes low-end inexpensive devices like Google Cardboard and high-end ones like HTC Vive or Oculus Rift, which are more expensive headsets. Using VR as a platform for content delivery allows better user engagement than other traditional methods, as VR headsets remove external distractions. Multi- user VR applications provide shared experiences where users can communicate and interact in the same virtual space. This shared environment, however, introduces challenges regarding network performance, quality of service (QoS) and sessions privacy. This paper presents a multi-user VR application and aims to evaluate network behaviour in a number of scenarios, including real VR headsets (i.e. Oculus Rift), as well as simulated ones. This QoS analysis is important for the understanding of how many VR users can be simultaneously connected with high image quality
Record statistics for biased random walks, with an application to financial data
We consider the occurrence of record-breaking events in random walks with
asymmetric jump distributions. The statistics of records in symmetric random
walks was previously analyzed by Majumdar and Ziff and is well understood.
Unlike the case of symmetric jump distributions, in the asymmetric case the
statistics of records depends on the choice of the jump distribution. We
compute the record rate , defined as the probability for the th
value to be larger than all previous values, for a Gaussian jump distribution
with standard deviation that is shifted by a constant drift . For
small drift, in the sense of , the correction to
grows proportional to arctan and saturates at the value
. For large the record rate approaches a
constant, which is approximately given by
for .
These asymptotic results carry over to other continuous jump distributions with
finite variance. As an application, we compare our analytical results to the
record statistics of 366 daily stock prices from the Standard & Poors 500
index. The biased random walk accounts quantitatively for the increase in the
number of upper records due to the overall trend in the stock prices, and after
detrending the number of upper records is in good agreement with the symmetric
random walk. However the number of lower records in the detrended data is
significantly reduced by a mechanism that remains to be identified.Comment: 16 pages, 7 figure
Signature of long-lived memory CD8+ T cells in acute SARS-CoV-2 infection
Immunological memory is a hallmark of adaptive immunity and facilitates an accelerated and enhanced immune response upon re-infection with the same pathogen. Since the outbreak of the ongoing COVID-19 pandemic, a key question has focused on which SARS-CoV-2-specific T cells stimulated during acute infection give rise to long-lived memory T cells. Here, using spectral flow cytometry combined with cellular indexing of transcriptomes and T cell receptor sequencing, we longitudinally characterized individual SARS-CoV-2-specific CD8 T cells of patients with COVID-19 from acute infection to 1 year into recovery and found a distinct signature identifying long-lived memory CD8 T cells. SARS-CoV-2-specific memory CD8 T cells persisting 1 year after acute infection express CD45RA, IL-7 receptor-α and T cell factor 1, but they maintain low expression of CCR7, thus resembling CD45RA effector memory T cells. Tracking individual clones of SARS-CoV-2-specific CD8 T cells, we reveal that an interferon signature marks clones that give rise to long-lived cells, whereas prolonged proliferation and mechanistic target of rapamycin signalling are associated with clonal disappearance from the blood. Collectively, we describe a transcriptional signature that marks long-lived, circulating human memory CD8 T cells following an acute viral infection
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