The triviality of the scalar sector of the standard one-doublet Higgs model implies that this model is only an effective low-energy theory valid below some cut-off scale Λ. The underlying high-energy ...theory must include flavor dynamics at a scale of order Λ or greater in order to give rise to the different Yukawa couplings of the Higgs to ordinary fermions. This flavor dynamics will generically produce flavor-changing neutral currents and non-universal corrections to
Z → b
b
. We show that the experimental constraints on the neutral
D-meson mass difference imply that Λ must be greater than of order 21 TeV. We also discuss bounds on Λ from the constraints on extra contributions to the
K
L
-
K
S
mass difference and to the coupling of the
Z boson to
b-quarks. For theories defined about the infrared-stable Gaussian fixed-point, we estimate that this lower bound on Λ yields an upper bound of approximately 460 GeV on the Higgs boson's mass, independent of the regulator chosen to define the theory.
The ununified standard model is an extension of the standard model that contains separate electroweak gauge groups for quarks and leptons. When it was originally proposed, data allowed the new gauge ...bosons to be quite light. We use recent data from precision electroweak measurements to put stringent bounds on the ununified standard model. In particular, at the 95% confidence level, we find that the ununified gauge bosons must have masses above about 2 TeV.
A series of complexes FeIV(O)(TMC)(X)+ (where X = OH−, CF3CO2 −, N3 −, NCS−, NCO−, and CN−) were obtained by treatment of the well-characterized nonheme oxoiron(IV) complex FeIV(O)(TMC)(NCMe)2+ (TMC ...= tetramethylcyclam) with the appropriate NR4X salts. Because of the topology of the TMC macrocycle, the FeIV(O)(TMC)(X)+ series represents an extensive collection of S = 1 oxoiron(IV) complexes that only differ with respect to the ligand trans to the oxo unit. Electronic absorption, Fe K-edge X-ray absorption, resonance Raman, and Mössbauer data collected for these complexes conclusively demonstrate that the characteristic spectroscopic features of the S = 1 FeIVO unit, namely, (i) the near-IR absorption properties, (ii) X-ray absorption pre-edge intensities, and (iii) quadrupole splitting parameters, are strongly dependent on the identity of the trans ligand. However, on the basis of extended X-ray absorption fine structure data, most FeIV(O)(TMC)(X)+ species have FeO bond lengths similar to that of FeIV(O)(TMC)(NCMe)2+ (1.66 ± 0.02 Å). The mechanisms by which the trans ligands perturb the FeIVO unit were probed using density functional theory (DFT) computations, yielding geometric and electronic structures in good agreement with our experimental data. These calculations revealed that the trans ligands modulate the energies of the FeO σ- and π-antibonding molecular orbitals, causing the observed spectroscopic changes. Time-dependent DFT methods were used to aid in the assignment of the intense near-UV absorption bands found for the oxoiron(IV) complexes with trans N3 −, NCS−, and NCO− ligands as X−-to-FeIVO charge-transfer transitions, thereby rationalizing the resonance enhancement of the ν(FeO) mode upon excitation of these chromophores.
A flavorful top-coloron model Chivukula, R. Sekhar; Simmons, Elizabeth H.; Vignaroli, Natascia
Physical review. D, Particles, fields, gravitation, and cosmology,
04/2013, Letnik:
87, Številka:
7
Journal Article
Recenzirano
Odprti dostop
In this paper we introduce a simple renormalizable model of an extended color gauge sector in which the third-generation quarks couple differently than the lighter quarks. In addition to a set of ...heavy color-octet vector bosons (colorons), the model also contains a set of heavy weak vector quarks. Mixing between the third generation of quarks and the first two is naturally small and occurs only through the (suppressed) mixing of all three generations with the heavy vector quarks. We discuss the constraints on this model arising from limits on flavor-changing neutral currents and from collider searches for the colorons and vector quarks, and discuss the prospects for discovery at the LHC.
Experiments at the LHC may yet discover a dijet resonance indicative of beyond the standard model (BSM) physics. In this case, the question becomes: what BSM theories are consistent with the ...unexpected resonance? One possibility would be a spin-2 object called the 'colorphilic graviton'-a spin-2 color-singlet particle which couples exclusively to the quark and gluon stress-energy tensors. We assess the possibility of this state's discovery in the dijet channel as an s-channel resonance, and report the regions of parameter space where colorphilic gravitons have not yet been excluded by LHC-13 data but still may be discovered in the dijet channel at LHC-14 for integrated luminosities of 0.3, 1, and 3 ab−1. We then delineate which of those regions remain accessible to future collider searches, once one accounts for applicability of the narrow-width approximation, mass resolution of the detector, and self-consistency according to tree-level partial-wave unitarity. We discover that-despite the strong constraints unitarity imposes on collider searches-the colorphilic graviton remains potentially discoverable in the LHC dijet channel. A means of investigation would be to apply the color discriminant variable, a dimensionless combination of quantities (production cross-section, total decay width, and invariant mass) that can be quickly measured after the discovery of a dijet resonance. Previous publications have demonstrated the color discriminant variable's utility when applied to theories containing vector bosons (colorons, Z ′ ), excited quarks, and diquarks. We extend this analysis to the case of the colorphilic graviton by applying the color discriminant variable to the appropriate region of parameter space. We conclude that resolvable, discoverable dijet resonances consistent with colorphilic gravitons span a narrower range of masses than those consistent with leptophobic Z ′ models, and can be distinguished from those originating from coloron, excited quark, and diquark models.
Successful occlusion of cerebral aneurysms using coil embolization is contingent upon stable thrombus formation, and the quality of the thrombus depends upon the biomechanical environment. The goal ...of this study was to investigate how coil embolization alters the mechanical micro-environment within the aneurysm dome. Inertialess particles were injected in three-dimensional, computational simulations of flow inside patient aneurysms using patient-specific boundary conditions. Coil embolization was simulated as a homogenous porous medium of known permeability and inertial constant. Lagrangian particle tracking was used to calculate the residence time and shear stress history for particles in the flow before and after treatment. The percentage of particles entering the aneurysm dome correlated with the neck surface area before and after treatment (pretreatment: R2 = 0.831, P < 0.001; post-treatment: R2 = 0.638, P < 0.001). There was an inverse relationship between the change in particles entering the dome and coil packing density (R2 = 0.600, P < 0.001). Following treatment, the particles with the longest residence times tended to remain within the dome even longer while accumulating lower shear stress. A significant correlation was observed between the treatment effect on residence time and the ratio of the neck surface area to porosity (R2 = 0.390, P = 0.007). The results of this study suggest that coil embolization triggers clot formation within the aneurysm dome via a low shear stress-mediated pathway. This hypothesis links independently observed findings from several benchtop and clinical studies, furthering our understanding of this treatment strategy.
The renormalizable coloron model, which has previously been shown in the literature to be consistent with a wide array of theoretical and precision electroweak constraints, includes a pair of ...spinless bosons (one scalar, one pseudoscalar). We show that either of them, or both together if they are degenerate, could be responsible for the diphoton resonance signal for which both CMS and ATLAS have seen evidence. Because either of these bosons would be produced and decay through loops of spectator fermions, the absence of signals in dijet, tt, and electroweak boson pair channels is not a surprise.
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