202 research outputs found
Excited-state contribution to the axial-vector and pseudo-scalar correlators with two extra pions
We study multi-particle state contributions to the QCD two-point functions of
the axial-vector and pseudo-scalar quark bilinears in a finite spatial volume.
For sufficiently small quark masses one expects three-meson states with two
additional pions at rest to have the lowest total energy after the ground
state. We calculate this three-meson state contribution using chiral
perturbation theory. We find it to be strongly suppressed and too small to be
seen in present-day lattice simulations.Comment: 17 pages, 5 figure
First-order restoration of SU(Nf) x SU(Nf) chiral symmetry with large Nf and Electroweak phase transition
It has been argued by Pisarski and Wilczek that finite temperature
restoration of the chiral symmetry SU(Nf) x SU(Nf) is first-order for Nf >=3.
This type of chiral symmetry with a large Nf may appear in the Higgs sector if
one considers models such as walking technicolor theories. We examine the
first-order restoration of the chiral symmetry from the point of view of the
electroweak phase transition. The strength of the transition is estimated in
SU(2) x U(1) gauged linear sigma model by means of the finite temperature
effective potential at one-loop with the ring improvement. Even if the mass of
the neutral scalar boson corresponding to the Higgs boson is larger than 114
GeV, the first-order transition can be strong enough for the electroweak
baryogenesis, as long as the extra massive scalar bosons (required for the
linear realization) are kept heavier than the neutral scalar boson. Explicit
symmetry breaking terms reduce the strength of the first-order transition, but
the transition can remain strongly first-order even when the masses of pseudo
Nambu-Goldstone bosons become as large as the current lower bound of direct
search experiments.Comment: 18 pages, 18 figures, minor corrections, references adde
Twisted mass fermions: neutral pion masses from disconnected contributions
Twisted mass fermions allow light quarks to be explored but with the
consequence that there are mass splittings, such as between the neutral and
charged pion. Using a direct calculation of the connected neutral pion
correlator and stochastic methods to evaluate the disconnected correlations, we
determine the neutral pion mass. We explore the dependence on lattice spacing
and quark mass in quenched QCD. For dynamical QCD, we determine the sign of the
splitting which is linked, via chiral PT, to the nature of the phase transition
at small quark mass.Comment: 6 pages, poster (hadron spectrum and quark masses) at Lattice
2005,Dublin, July 25-3
Charm quark system at the physical point of 2+1 flavor lattice QCD
We investigate the charm quark system using the relativistic heavy quark
action on 2+1 flavor PACS-CS configurations previously generated on lattice. The dynamical up-down and strange quark masses are set to
the physical values by using the technique of reweighting to shift the quark
hopping parameters from the values employed in the configuration generation. At
the physical point, the lattice spacing equals GeV and the
spatial extent fm. The charm quark mass is determined by the
spin-averaged mass of the 1S charmonium state, from which we obtain m_{\rm
charm}^{\msbar}(\mu = m_{\rm charm}^{\msbar}) = 1.260(1)(6)(35) GeV, where the
errors are due to our statistics, scale determination and renormalization
factor. An additional systematic error from the heavy quark is of order
, which is estimated to be a percent
level if the factor analytic in is of order unity. Our
results for the charmed and charmed-strange meson decay constants are
MeV, MeV, again up to the heavy quark
errors of order . Combined with the CLEO
values for the leptonic decay widths, these values yield , , where the last error is on
account of the experimental uncertainty of the decay widths.Comment: 16 pages, 12 figure
Electromagnetic form factor of pion from N_f=2+1 dynamical flavor QCD
We present a calculation of the electromagnetic form factor of the pion in
flavor lattice QCD. Calculations are made on the PACS-CS gauge field
configurations generated using Iwasaki gauge action and Wilson-clover quark
action on a lattice volume with the lattice spacing estimated as
fm at the physical point. Measurements of the form factor are
made using the technique of partially twisted boundary condition to reach small
momentum transfer as well as periodic boundary condition with integer momenta.
Additional improvements including random wall source techniques and a judicious
choice of momenta carried by the incoming and outgoing quarks are employed for
error reduction. Analyzing the form factor data for the pion mass at MeV and 296 MeV, we find that the NNLO SU(2) chiral perturbation
theory fit yields for the pion charge radius
at the physical pion mass. Albeit the error is quite large, this is consistent
with the experimental value of . Below MeV, we find that statistical fluctuations in the pion two- and
three-point functions become too large to extract statistically meaningful
averages on a spatial volume. We carry out a sample calculation on a
lattice with the quark masses close to the physical point, which
suggests that form factor calculations at the physical point become feasible by
enlarging lattice sizes to .Comment: 28 pages, 14 figure
Novel Approach to Super Yang-Mills Theory on Lattice - Exact fermionic symmetry and "Ichimatsu" pattern -
We present a lattice theory with an exact fermionic symmetry, which mixes the
link and the fermionic variables. The staggered fermionic variables may be
reconstructed into a Majorana fermion in the continuum limit. The gauge action
has a novel structure. Though it is the ordinary plaquette action, two
different couplings are assigned in the ``Ichimatsu pattern'' or the checkered
pattern. In the naive continuum limit, the fermionic symmetry survives as a
continuum (or an ) symmetry. The transformation of the fermion is
proportional to the field strength multiplied by the difference of the two
gauge couplings in this limit. This work is an extension of our recently
proposed cell model toward the realization of supersymmetric Yang-Mills theory
on lattice.Comment: 26 pages, 4 figure
A novel mutation in the tyrosine kinase domain of ERBB2 in hepatocellular carcinoma
BACKGROUND: Several studies showed that gain-of-function somatic mutations affecting the catalytic domain of EGFR in non-small cell lung carcinomas were associated with response to gefitinib and erlotinib, both EGFR-tyrosine kinase inhibitors. In addition, 4% of non-small cell lung carcinomas were shown to have ERBB2 mutations in the kinase domain. In our study, we sought to determine if similar respective gain-of-function EGFR and ERBB2 mutations were present in hepatoma and/or biliary cancers. METHODS: We extracted genomic DNA from 40 hepatoma (18) and biliary cancers (22) samples, and 44 adenocarcinomas of the lung, this latter as a positive control for mutation detection. We subjected those samples to PCR-based semi-automated double stranded nucleotide sequencing targeting exons 18–21 of EGFR and ERBB2. All samples were tested against matched normal DNA. RESULTS: We found 11% of hepatoma, but no biliary cancers, harbored a novel ERBB2 H878Y mutation in the activating domain. CONCLUSION: These newly described mutations may play a role in predicting response to EGFR-targeted therapy in hepatoma and their role should be explored in prospective studies
Detection of a climatological short break in the polar night jet in early winter and its relation to cooling over Siberia
The polar night jet (PNJ) is a strong stratospheric westerly circumpolar wind
at around 65° N in winter, and the strength of the climatological
PNJ is widely recognized to increase from October through late December.
Remarkably, the climatological PNJ temporarily stops increasing during late
November. We examined this short break in terms of the atmospheric dynamical
balance and the climatological seasonal march. We found that it results from
an increase in the upward propagation of climatological planetary waves from
the troposphere to the stratosphere in late November, which coincides with a
maximum of the climatological Eliassen–Palm (EP) flux convergence in the lower
stratosphere. The upward propagation of planetary waves at 100 hPa, which is
strongest over Siberia, is related to the climatological strengthening of the
tropospheric trough over Siberia. We suggest that longitudinally asymmetric
forcing by land–sea heating contrasts caused by their different heat
capacities can account for the strengthening of the trough.</p
The Polar Amplification Model Intercomparison Project (PAMIP) contribution to CMIP6: Investigating the causes and consequences of polar amplification
This is the final version. Available on open access from the European Geosciences Union via the DOI in this recordPolar amplification-the phenomenon where external radiative forcing produces a larger change in surface temperature at high latitudes than the global average-is a key aspect of anthropogenic climate change, but its causes and consequences are not fully understood. The Polar Amplification Model Intercomparison Project (PAMIP) contribution to the sixth Coupled Model Intercomparison Project (CMIP6; Eyring et al., 2016) seeks to improve our understanding of this phenomenon through a coordinated set of numerical model experiments documented here. In particular, PAMIP will address the following primary questions: (1) what are the relative roles of local sea ice and remote sea surface temperature changes in driving polar amplification? (2) How does the global climate system respond to changes in Arctic and Antarctic sea ice? These issues will be addressed with multi-model simulations that are forced with different combinations of sea ice and/or sea surface temperatures representing present-day, pre-industrial and future conditions. The use of three time periods allows the signals of interest to be diagnosed in multiple ways. Lower-priority tier experiments are proposed to investigate additional aspects and provide further understanding of the physical processes. These experiments will address the following specific questions: what role does ocean-atmosphere coupling play in the response to sea ice? How and why does the atmospheric response to Arctic sea ice depend on the pattern of sea ice page1140 forcing? How and why does the atmospheric response to Arctic sea ice depend on the model background state? What have been the roles of local sea ice and remote sea surface temperature in polar amplification, and the response to sea ice, over the recent period since 1979? How does the response to sea ice evolve on decadal and longer timescales? A key goal of PAMIP is to determine the real-world situation using imperfect climate models. Although the experiments proposed here form a coordinated set, we anticipate a large spread across models. However, this spread will be exploited by seeking "emergent constraints" in which model uncertainty may be reduced by using an observable quantity that physically explains the intermodel spread. In summary, PAMIP will improve our understanding of the physical processes that drive polar amplification and its global climate impacts, thereby reducing the uncertainties in future projections and predictions of climate change and variability.DECC/Defra Met Office Hadley Centre Climate ProgrammeEuropean Union Horizon 2020Natural Environment Research Council (NERC)National Science Foundation (NSF)Korean Polar Research InstituteBMBFArCSInderDe
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