1,721,109 research outputs found
Improved bounds for CFT's with global symmetries
No full textThe four point functions of Conformal Field Theories (CFT's) with global symmetries give rise to multiple crossing symmetry constraints. We explicitly study the correlator of four scalar operators transforming in the fundamental representation of a global SO(N) and the correlator of chiral and anti-chiral super fields in a superconformal field theory. In both cases the constraints take the form of a triple sum rule, whose feasibility can be translated into restrictions on the CFT spectrum and interactions. In the case of SO(N) global symmetry we derive bounds for the first scalar singlet operator entering the Operator Product Expansion (OPE) of two fundamental representations for different value of N. Bounds for the first scalar traceless-symmetric representation of the global symmetry are computed as well. Results for superconformal field theories improve previous investigations due to the use of the full set of constraints. Our analysis only assumes unitarity of the CFT, crossing symmetry of the four point function and existence of an OPE for scalars. © SISSA 2012
Anomalous dimensions of scalar operators in CFT
No full textWe present a recently developed method to constrain the anomalous dimension of scalar operators in a general Conformal Field Theory (CFT). Using a consistency condition derived from four-point correlation functions it is possible to birid the anomalous dimension of a composite operator phi(2). The result has also consequences on model building.LPT
Production of a composite Higgs boson
No full textWe present a model-independent prescription for computing the gluon fusion production rate of a composite Higgs boson, which arises as a pseudo-Nambu-Goldstone boson, using effective Lagrangians. The calculation incorporates three different effects due to the composite nature of the Higgs, some of which were neglected previously. We apply the prescription to models with and without the collective breaking mechanism. In sharp contrast with the case of a fundamental Higgs scalar, the rate only depends on the decay constant f and is not sensitive to masses of new particles. After including electroweak constraints, there is a substantial reduction in the rate, in the range of 10%-30% or greater. © 2011 American Physical Society
T-parity, its problems and their solution
No full textWe point out a basic difficulty in the construction of little-Higgs models with T-parity which is overlooked by large part of the present literature. Almost all models proposed so far fail to achieve their goal: they either suffer from sizable electroweak corrections or from a breakdown of collective breaking. We provide a model building recipe to bypass the above problem and apply it to build the simplest T-invariant extension of the Littlest Higgs. Our model predicts additional T-odd pseudo-Goldstone bosons with weak scale masses. © SISSA 2011
Universal constraints on conformal operator dimensions
Full text linkWe continue the study of model-independent constraints on the unitary conformal field theories (CFTs) in four dimensions, initiated in. Our main result is an improved upper bound on the dimension Δ of the leading scalar operator appearing in the operator product expansion (OPE) of two identical scalars of dimension d: φ d≠1+O δ+.... In the interval 1<1.7 this universal bound takes the form Δ≤2+0.7(d-1)1/2+2. 1(d-1)+0.43(d-1)3/2. The proof is based on prime principles of CFT: unitarity, crossing symmetry, OPE, and conformal block decomposition. We also discuss possible applications to particle phenomenology and, via a 2D analogue, to string theory. © 2009 The American Physical Society
Clinical procedure for luting glass-fiber posts
No full textPurpose: This report presents clinical cases in which a self-activating dual-cure adhesive system was used in combination with proprietary self-curing resin cement for bonding a translucent glass-fiber post. The clinical luting procedure of a self-activating bonding/self-curing resin cement system in combination with a glass-fiber post based on fiber-reinforced technology is documented. Materials and Methods: The glass-fiber post was placed into a root canal preparation under clinical conditions and documented. A few restored teeth were extracted after 1 week and processed for SEM observations to determine the bonding mechanism to root dentin under clinical conditions. Results: The SEM observations clearly showed that the bonding mechanism between Excite Dual Cure and root dentin was based on hybrid layer, resin tag, and adhesive lateral branch formation. Conclusion: The luting procedure described is simple and easy, and can be proposed as a daily clinical technique
Mixed scalar-current bootstrap in three dimensions
No full textWe study the mixed system of correlation functions involving a scalar field charged under a global U(1) symmetry and the associated conserved spin-1 current Jμ. Using numerical bootstrap techniques we obtain bounds on new observables not accessible in the usual scalar bootstrap. We then specialize to the O(2) model and extract rigorous bounds on the three-point function coefficient of two currents and the unique relevant scalar singlet, as well as those of two currents and the stress tensor. Using these results, and comparing with a quantum Monte Carlo simulation of the O(2) model conductivity, we give estimates of the thermal one-point function of the relevant singlet and the stress tensor. We also obtain new bounds on operators in various sectors
Comparison between two clinical procedures for bonding fiber posts into a root canal: a microscopic investigation
No full textThe purpose of this study was to evaluate the influence of two brushes used as carriers of a primer-adhesive solution as to the formation of resin tags, adhesive lateral branches, and a hybrid layer when used to bond translucent fiber posts. Twenty endodontically treated teeth, extracted for periodontal reasons, were used. The samples were randomly divided into two groups of 10 samples each (Group 1: Microbrush Scotchbond 1 Rely X ARC resin cement; Group 2: small plastic brush Scotchbond 1 Rely X ARC resin cement). The adhesive system and resin cement were used strictly following manufacturers' instructions. The priming-adhesive solution of the one-bottle system was light-cured before placing the resin cement and the post. Twenty translucent fiber posts were used. After luting procedures, root samples were processed for SEM observations. The adhesive system showed a resin dentin interdiffusion zone (RDIZ), resin tag, and adhesive lateral branch formation. Microscopic examination of restored interfaces of group 1 showed a higher percentage (p < 0.05) of RDIZ than those found in samples of group 2. In group 1 samples, RDIZ morphology was well detectable and uniform in all thirds of the root canals. In group 2, RDIZ was not visible in the apical third. No statistically significant differences were found among the two groups coronally and at the middle third, but the apical third of group 1 showed significantly more resin tag formation than group 2. The characteristic reverse cone shape of resin tags was always noted in the coronal and middle third of the root canals of both groups and in the apical third of group 1. In the apical third of group 2 root canals, the resin tags showed a less uniform morphology and a shorter length than those found in the other observed thirds. Copyright © 2002 by The American Association of Endodontists
Clinical evaluation of fiber-reinforced epoxy resin posts and cast post and cores
No full textPurpose: This retrospective study evaluated treatment outcome of cast post and core and Composipost systems after 4 yrs of clinical service. Materials and Methods: 200 patients were included in the study. They were divided in two groups of 100 endodontically treated teeth restored with a post. Group 1: Composipost systems were luted into root canal following the manufacturer's instructions. Group 2: Cast post and cores were cemented into root canal preparations with a traditional technique. The patients were recalled after 6 months, 1, 2 and 4 yrs and clinical and radiographic examinations were completed. Endodontic and prosthodontic results were recorded. Results: Group 1: 95% of the teeth restored with Composiposts showed clinical success; 3% of these samples were excluded for noncompliance and 2% showed endodontic failure. Group 2: Clinical success was found with 84% of teeth restored with cast post and core. 2% of these samples were excluded for noncompliance, 9% showed root fracture, 2% dislodgment of crown and 3% endodontic failure. Statistical evaluation showed significant differences between Groups 1 and 2 (P< 0.001). The results of this retrospective study indicated that the Composipost system was superior to the conventional cast post and core system after 4 yrs of clinical service
Bounds in 4D conformal field theories with global symmetry
No full textWe explore the constraining power of OPE associativity in 4D conformal field theory with a continuous global symmetry group. We give a general analysis of crossing symmetry constraints in the 4-point function (φφφ †φ†, where φ is a primary scalar operator in a given representation R. These constraints take the form of 'vectorial sum rules' for conformal blocks of operators whose representations appear in R ⊗ R and R ⊗ R̄. The coefficients in these sum rules are related to the Fierz transformation matrices for the R ⊗ R ⊗ R̄ ⊗ R̄ invariant tensors. We show that the number of equations is always equal to the number of symmetry channels to be constrained. We also analyze in detail two cases-the fundamental of SO(N) and the fundamental of SU(N). We derive the vectorial sum rules explicitly, and use them to study the dimension of the lowest singlet scalar in the φ × φ† OPE. We prove the existence of an upper bound on the dimension of this scalar. The bound depends on the conformal dimension of φ and approaches 2 in the limit dim(φ) → 1. For several small groups, we compute the behavior of the bound at dim(φ) > 1. We discuss implications of our bound for the conformal technicolor scenario of electroweak symmetry breaking. © 2011 IOP Publishing Ltd
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