62 research outputs found
Axion cosmology, lattice QCD and the dilute instanton gas
Axions are one of the most attractive dark matter candidates. The evolution
of their number density in the early universe can be determined by calculating
the topological susceptibility of QCD as a function of the
temperature. Lattice QCD provides an ab initio technique to carry out such a
calculation. A full result needs two ingredients: physical quark masses and a
controlled continuum extrapolation from non-vanishing to zero lattice spacings.
We determine in the quenched framework (infinitely large quark
masses) and extrapolate its values to the continuum limit. The results are
compared with the prediction of the dilute instanton gas approximation (DIGA).
A nice agreement is found for the temperature dependence, whereas the overall
normalization of the DIGA result still differs from the non-perturbative
continuum extrapolated lattice results by a factor of order ten. We discuss the
consequences of our findings for the prediction of the amount of axion dark
matter.Comment: 9 pages, 7 figure
Effective potential and vacuum stability
By following previous work on this subject, we investigate the issue of the
instability of the electroweak vacuum against the top loop corrections by
performing an accurate analysis of a Higgs-Yukawa model. We find that, when the
physical cutoff is properly implemented in the theory, the potential does not
exhibit any instability. Moreover, contrary to recent claims, we show that this
instability cannot be understood in terms of the very insightful work of Wu and
Weinberg on the non-convexity of the one-loop effective potential of a scalar
theory. Some of the theoretical and phenomenological consequences of our
results are briefly discussed.Comment: 10 pages, 4 figure
The running coupling of 8 flavors and 3 colors
We compute the renormalized running coupling of SU(3) gauge theory coupled to
N_f = 8 flavors of massless fundamental Dirac fermions. The recently proposed
finite volume gradient flow scheme is used. The calculations are performed at
several lattice spacings allowing for a controlled continuum extrapolation. The
results for the discrete beta-function show that it is monotonic without any
sign of a fixed point in the range of couplings we cover. As a cross check the
continuum results are compared with the well-known perturbative continuum
beta-function for small values of the renormalized coupling and perfect
agreement is found.Comment: 15 pages, 17 figures, published versio
On the charge density and asymptotic tail of a monopole
We propose a new definition for the abelian magnetic charge density of a nonabelian monopole, based on zero-modes of an associated Dirac operator. Unlike the standard definition of the charge density, this density is smooth in the core of the monopole. We show that this charge density induces a magnetic field whose expansion in powers of 1=r agrees with that of the conventional asymptotic magnetic field to all orders. We also show that the asymptotic field can be easily calculated from the spectral curve. Explicit examples are given for known monopole solutions
Carbonic anhydrase XII is a marker of good prognosis in invasive breast carcinoma
Hypoxia and pH influence gene expression in tumours, and it is becoming increasingly clear that the pattern of genes expressed by a tumour determines its growth and survival characteristics. Hypoxia-inducible factor-1 (HIF-1) is a key mediator of the cellular response to hypoxia and high HIF-1 expression has been identified as a poor prognostic factor in tumours. Recently, we identified the tumour-associated carbonic anhydrases (CA), CA9 and CA12 as hypoxia-inducible in tumour cell lines. Furthermore, we identified CA IX to be a poor prognostic factor in breast cancer. The aim of this study was to assess the prognostic significance of CA XII. CA XII expression was studied by immunohistochemistry in a series of 103 cases of invasive breast cancer and any association with recognised prognostic factors or relation with the outcome was examined. CA XII expression was present in 77 out of 103 (75%) cases and was associated with lower grade (P=0.001), positive estrogen receptor status (P<0.001), and negative epidermal growth factor receptor status (P<0.001). Furthermore, although CA XII expression was associated with an absence of necrosis (P<0.001), expression of CA XII in some high-grade tumours was induced in regions directly adjacent to morphological necrosis. Additionally, using univariate analysis, CA XII positive tumours were associated with a lower relapse rate (P=0.04) and a better overall survival (P=0.01). In conclusion, CA XII expression is influenced both by factors related to differentiation and hypoxia in breast cancer in vivo and CA XII expression is associated with a better prognosis in an unselected series of invasive breast carcinoma patients
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