ABSTRACT
We propose a scenario to retrodict the top and bottom mass and the Abelian gauge coupling from first principles in a microscopic model including quantum gravity. In our approximation, antiscreening quantum-gravity fluctuations induce an asymptotically safe fixed point for the Abelian hypercharge leading to a uniquely fixed infrared value that is observationally viable for a particular choice of microscopic gravitational parameters. The unequal quantum numbers of the top and bottom quark lead to different fixed-point values for the top and bottom Yukawa couplings under the impact of gauge and gravity fluctuations. This results in a dynamically generated mass difference between the two quarks. To work quantitatively, the preferred ratio of electric charges of bottom and top in our approximation lies in close vicinity to the standard-model value of Q_{b}/Q_{t}=-1/2.
ABSTRACT
We explore universal critical behavior in models with two competing order parameters, and an O(N) âO(M) symmetry for dimensions d≤3. In d=3, there is always exactly one stable renormalization group fixed point, corresponding to bicritical or tetracritical behavior. Employing pseudospectral techniques to solve functional renormalization group equations in a two-dimensional field space, we uncover a more intricate structure of fixed points in d<3, where two additional bicritical fixed points play a role. Towards d=2, we discover ranges of N=M with several simultaneously stable fixed points, indicating the coexistence of several universality classes.
ABSTRACT
We employ the nonperturbative functional renormalization group to study models with an O(N(1) âO(N)(2)) symmetry. Here different fixed points exist in three dimensions, corresponding to bicritical and tetracritical behavior induced by the competition of two order parameters. We discuss the critical behavior of the symmetry-enhanced isotropic, the decoupled and the biconical fixed point, and analyze their stability in the N(1),N(2) plane. We study the fate of nontrivial fixed points during the transition from three to four dimensions, finding evidence for a triviality problem for coupled two-scalar models in high-energy physics. We also point out the possibility of noncanonical critical exponents at semi-Gaussian fixed points and show the emergence of Goldstone modes from discrete symmetries.
ABSTRACT
OBJECTIVE: To better characterize the dermoscopic patterns of mucosal lesions in relation to the histopathologic characteristics. DESIGN: Retrospective and observational study. SETTING: Fourteen referral pigmented lesion clinics in 10 countries. PATIENTS: A total of 140 pigmented mucosal lesions (126 benign lesions, 11 melanomas, 2 Bowen disease lesions, and 1 metastasis) from 92 females (66%) and 48 males (34%) were collected from October 2007 through November 2008. MAIN OUTCOME MEASURES: Scoring the dermoscopic patterns (dots, globules, or clods, circles, lines, or structureless) and colors (brown, black, blue, gray, red, purple, and white) and correlation with the histopathologic characteristics. RESULTS: Based on univariate analysis and 2 diagnostic models, the presence of structureless zones inside the lesions with blue, gray, or white color (the first model) had a 100% sensitivity for melanoma and 92.9% sensitivity for any malignant lesion, and 82.2% and 83.3% specificity for benign lesions in the group with melanoma lesions and the group with malignant lesions, respectively. Based on the colors (blue, gray, or white) only (the second model), the sensitivity for the group with melanoma was 100% and for the group with any malignant lesion was 92.9%, and the specificity was 64.3% and 65.1%, respectively. Patients with malignant lesions were significantly older than patients with benign lesions (mean [SD] ages, 60.1 [22.8] years vs 43.2 [17.3] years, respectively). CONCLUSION: The combination of blue, gray, or white color with structureless zones are the strongest indicators when differentiating between benign and malignant mucosal lesions in dermoscopy.