113 research outputs found
Chiral Symmetry in Two-Color QCD at Finite Temperature
We study the chiral symmetry in two-color QCD with N massless flavors at
finite temperature, using an effective theory. For the gauge group SU(2), the
chiral symmetry is enlarged to SU(2N), which is then spontaneously broken to
Sp(2N) at zero temperature. At finite temperature, and when the axial anomaly
can be neglected, we find a first order phase transition occurring for two or
more flavors. In the presence of instantons, the symmetry restoration
unambiguously remains first order for three or more massless flavors. These
results could be relevant for lattice studies of chiral symmetry at finite
temperature and density.Comment: 10 pages, Revte
Scaling and Goldstone effects in a QCD with two flavours of adjoint quarks
We study QCD with two Dirac fermions in the adjoint representation at finite
temperature by Monte Carlo simulations.In such a theory the deconfinement and
chiral phase transitions occur at different temperatures. We locate the second
order chiral transition point at beta_c=5.624(2) and show that the scaling
behaviour of the chiral condensate in the vicinity of beta_c is in full
agreeement with that of the 3d O(2) universality class, and to a smaller extent
comparable to the 3d O(6) class. From the previously determined first order
deconfinement transition point beta_d=5.236(3) and the two-loop beta function
we find the ratio T_c/T_d = 7.8(2). In the region between the two phase
transitions we explicitly confirm the quark mass dependence of the chiral
condensate which is expected due to the existence of Goldstone modes like in 3d
O(N) spin models. At the deconfinement transition the condensate shows a gap,
and below beta_d, it is nearly mass-independent for fixed beta.Comment: 28 pages, 12 figures, Latex2
Derivative expansion of the renormalization group in O(N) scalar field theory
We apply a derivative expansion to the Legendre effective action flow
equations of O(N) symmetric scalar field theory, making no other approximation.
We calculate the critical exponents eta, nu, and omega at the both the leading
and second order of the expansion, associated to the three dimensional
Wilson-Fisher fixed points, at various values of N. In addition, we show how
the derivative expansion reproduces exactly known results, at special values
N=infinity,-2,-4, ... .Comment: 29 pages including 4 eps figures, uses LaTeX, epsfig, and latexsy
The 3-D O(4) universality class and the phase transition in two-flavor QCD
We determine the critical equation of state of the three-dimensional O(4)
universality class. We first consider the small-field expansion of the
effective potential (Helmholtz free energy). Then, we apply a systematic
approximation scheme based on polynomial parametric representations that are
valid in the whole critical regime, satisfy the correct analytic properties
(Griffiths' analyticity), take into account the Goldstone singularities at the
coexistence curve, and match the small-field expansion of the effective
potential. From the approximate representations of the equation of state, we
obtain estimates of several universal amplitude ratios.
The three-dimensional O(4) universality class is expected to describe the
finite-temperature chiral transition of quantum chromodynamics with two light
flavors. Within this picture, the O(4) critical equation of state relates the
reduced temperature, the quark masses, and the condensates around T_c in the
limit of vanishing quark masses.Comment: 19 pages, 5 fig
Anti-Ferromagnetic Condensate in Yang-Mills Theory
SU(2) gauge theory with competing interactions is shown to possess a rich
phase structure with anti-ferromagnetic vacua. It is argued that the phase
boundaries persist in the weak coupling limit suggesting the existence of
different renormalized continuum theories for QCD.Comment: 26 pages of LaTeX with 8 PostScript figures, uses elsart style file,
new version accepted for publication in Nucl. Phys.
On the nature of the finite-temperature transition in QCD
We discuss the nature of the finite-temperature transition in QCD with N_f
massless flavors. Universality arguments show that a continuous (second-order)
transition must be related to a 3-D universality class characterized by a
complex N_f X N_f matrix order parameter and by the symmetry-breaking pattern
[SU(N_f)_L X SU(N_f)_R]/Z(N_f)_V -> SU(N_f)_V/Z(N_f)_V, or [U(N_f)_L X
U(N_f)_R]/U(1)_V -> U(N_f)_V/U(1)_V if the U(1)_A symmetry is effectively
restored at T_c. The existence of any of these universality classes requires
the presence of a stable fixed point in the corresponding 3-D Phi^4 theory with
the expected symmetry-breaking pattern. Otherwise, the transition is of first
order. In order to search for stable fixed points in these Phi^4 theories, we
exploit a 3-D perturbative approach in which physical quantities are expanded
in powers of appropriate renormalized quartic couplings. We compute the
corresponding Callan-Symanzik beta-functions to six loops. We also determine
the large-order behavior to further constrain the analysis. No stable fixed
point is found, except for N_f=2, corresponding to the symmetry-breaking
pattern [SU(2)_L X SU(2)_R]/Z(2)_V -> SU(2)_V/Z(2)_V equivalent to O(4) ->
O(3). Our results confirm and put on a firmer ground earlier analyses performed
close to four dimensions, based on first-order calculations in the framework of
the epsilon=4-d expansion. These results indicate that the finite-temperature
phase transition in QCD is of first order for N_f>2. A continuous transition is
allowed only for N_f=2. But, since the theory with symmetry-breaking pattern
[U(2)_L X U(2)_R]/U(1)_V -> U(2)_V/U(1)_V does not have stable fixed points,
the transition can be continuous only if the effective breaking of the U(1)_A
symmetry is sufficiently large.Comment: 30 pages, 3 figs, minor correction
Decreased IGF1R attenuates senescence and improves function in pancreatic β-cells
IntroductionThe enhanced β-cell senescence that accompanies insulin resistance and aging contributes to cellular dysfunction and loss of transcriptional identity leading to type 2 diabetes (T2D). While senescence is among the 12 recognized hallmarks of aging, its relation to other hallmarks including altered nutrient sensing (insulin/IGF1 pathway) in β-cells is not fully understood. We previously reported that an increased expression of IGF1R in mouse and human β-cells is a marker of older β-cells; however, its contribution to age-related dysfunction and cellular senescence remains to be determined.MethodsIn this study, we explored the direct role of IGF1R in β-cell function and senescence using two independent mouse models with decreased IGF1/IGF1R signaling: a) Ames Dwarf mice (Dwarf +/+), which lack growth hormone and therefore have reduced circulating levels of IGF1, and b) inducible β-cell-specific IGF1R knockdown (βIgf1rKD) mice.ResultsCompared to Dwarf+/- mice, Dwarf+/+ mice had lower body and pancreas weight, lower circulating IGF1 and insulin levels, and lower IGF1R and p21Cip1 protein expression in β-cells, suggesting the suppression of senescence. Adult βIgf1rKD mice showed improved glucose clearance and glucose-induced insulin secretion, accompanied by decreased p21Cip1 protein expression in β-cells. RNA-Seq of islets isolated from these βIgf1rKD mice revealed the restoration of three signaling pathways known to be downregulated by aging: sulfide oxidation, autophagy, and mTOR signaling. Additionally, deletion of IGF1R in mouse β-cells increased transcription of genes important for maintaining β-cell identity and function, such as Mafa, Nkx6.1, and Kcnj11, while decreasing senescence-related genes, such as Cdkn2a, Il1b, and Serpine 1. Decreased senescence and improved insulin-secretory function of β-cells were also evident when the βIgf1rKD mice were fed a high-fat diet (HFD; 60% kcal from fat, for 5 weeks).DiscussionThese results suggest that IGF1R signaling plays a causal role in aging-induced β-cell dysfunction. Our data also demonstrate a relationship between decreased IGF1R signaling and suppressed cellular senescence in pancreatic β-cells. Future studies can further our understanding of the interaction between senescence and aging, developing interventions that restore β-cell function and identity, therefore preventing the progression to T2D
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Examining the predictability of the Stratospheric Sudden Warming of January 2013 using multiple NWP systems
The first multi-model study to estimate the predictability of a boreal Sudden Stratospheric Warming (SSW) is performed using five NWP systems. During the 2012-2013 boreal winter, anomalous upward propagating planetary wave activity was observed towards the end of December, which followed by a rapid deceleration of the westerly circulation around 2 January 2013, and on 7 January 2013 the zonal mean zonal wind at 60°N and 10 hPa reversed to easterly. This stratospheric dynamical activity was followed by an equatorward shift of the tropospheric jet stream and by a high pressure anomaly over the North Atlantic, which resulted in severe cold conditions in the UK and Northern Europe. In most of the five models, the SSW event was predicted 10 days in advance. However, only some ensemble members in most of the models predicted weakening of westerly wind when the models were initialized 15 days in advance of the SSW. Further dynamical analysis of the SSW shows that this event was characterized by the anomalous planetary wave-1 amplification followed by the anomalous wave-2 amplification in the stratosphere, which resulted in a split vortex occurring between 6 January 2013 and 8 January 2013. The models have some success in reproducing wave-1 activity when initialized 15 days in advance, they but generally failed to produce the wave-2 activity during the final days of the event. Detailed analysis shows that models have reasonably good skill in forecasting tropospheric blocking features that stimulate wave-2 amplification in the troposphere, but they have limited skill in reproducing wave-2 amplification in the stratosphere
Two flavor chiral phase transition from nonperturbative flow equations
We employ nonperturbative flow equations to compute the equation of state for
two flavor QCD within an effective quark meson model. This yields the
temperature and quark mass dependence of quantities like the chiral condensate
or the pion mass. A precision estimate of the universal critical equation of
state for the three-dimensional O(4) Heisenberg model is presented. We
explicitly connect the O(4) universal behavior near the critical temperature
and zero quark mass with the physics at zero temperature and a realistic pion
mass. For realistic quark masses the pion correlation length near T_c turns out
to be smaller than its zero temperature value.Comment: 49 pages including 15 figures, LaTeX, uses epsf.sty and rotate.st
Theta dependence of SU(N) gauge theories in the presence of a topological term
We review results concerning the theta dependence of 4D SU(N) gauge theories
and QCD, where theta is the coefficient of the CP-violating topological term in
the Lagrangian. In particular, we discuss theta dependence in the large-N
limit.
Most results have been obtained within the lattice formulation of the theory
via numerical simulations, which allow to investigate the theta dependence of
the ground-state energy and the spectrum around theta=0 by determining the
moments of the topological charge distribution, and their correlations with
other observables. We discuss the various methods which have been employed to
determine the topological susceptibility, and higher-order terms of the theta
expansion. We review results at zero and finite temperature. We show that the
results support the scenario obtained by general large-N scaling arguments, and
in particular the Witten-Veneziano mechanism to explain the U(1)_A problem. We
also compare with results obtained by other approaches, especially in the
large-N limit, where the issue has been also addressed using, for example, the
AdS/CFT correspondence.
We discuss issues related to theta dependence in full QCD: the neutron
electric dipole moment, the dependence of the topological susceptibility on the
quark masses, the U(1)_A symmetry breaking at finite temperature.
We also consider the 2D CP(N) model, which is an interesting theoretical
laboratory to study issues related to topology. We review analytical results in
the large-N limit, and numerical results within its lattice formulation.
Finally, we discuss the main features of the two-point correlation function
of the topological charge density.Comment: A typo in Eq. (3.9) has been corrected. An additional subsection
(5.2) has been inserted to demonstrate the nonrenormalizability of the
relevant theta parameter in the presence of massive fermions, which implies
that the continuum (a -> 0) limit must be taken keeping theta fixe
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