Search results for "Dimension"

Hydrodynamical forces acting on particles in a two-dimensional flow near a solid wall

2000

The hydrodynamical forces acting on a single particle and on a random rigid array of particles suspended in a two-dimensional shear flow of Newtonian fluid near a rigid wall were studied numerically in the flow regime where the relevant Reynolds numbers are of the order of unity. The simulations were done with conventional finite volume method for single-particle cases and with lattice-Boltzmann method for many-particle cases. A set of comparison cases was solved with both methods in order to check the accuracy of the lattice-Boltzmann method. For the single-particle case analytic formulae for the longitudinal drag force and for the transverse lift force were found. A modification to Darcy'…

Multifractal wave functions at the Anderson transition.

1991

Electronic wave functions in disordered systems are studied within the Anderson model of localization. At the critical disorder in 3D we diagonalize very large (103 823\ifmmode\times\else\texttimes\fi{}103 823) secular matrices by means of the Lanczos algorithm. On all length scales the obtained strong spatial fluctuations of the amplitude of the eigenstates display a multifractal character, reflected in the set of generalized fractal dimensions and the singularity spectrum of the fractal measure. An analysis of 1D systems shows multifractality too, in contrast to previous claims.

Searches for Physics Beyond the Standard Model

2015

Despite its phenomenal success, the Standard Model is not expected to be a complete description of nature all the way up to the Planck scale where quantum gravity comes into play. As the collider at the current energy frontier, the LHC is in a unique position to look for signals of physics beyond the Standard Model. In this chapter, results from the first run of the LHC are surveyed that go beyond the supersymmetric extension of the Standard Model discussed in the previous chapter. At the time of writing, no evidence for new phenomena has been discovered. Instead, the LHC experiments have constrained the parameter space of conceivable models significantly. The most prominent results are on …

Higgs production and decay in models of a warped extra dimension with a bulk Higgs

2014

Warped extra-dimension models in which the Higgs boson is allowed to propagate in the bulk of a compact AdS5 space are conjectured to be dual to models featuring a partially composite Higgs boson. They offer a framework with which to investigate the implications of changing the scaling dimension of the Higgs operator, which can be used to reduce the constraints from electroweak precision data. In the context of such models, we calculate the cross section for Higgs production in gluon fusion and the H → γγ decay rate and show that they are finite (at one-loop order) as a consequence of gauge invariance. The extended scalar sector comprising the Kaluza-Klein excitations of the Standard Model …

A simple microsuperspace model in 2 + 1 spacetime dimensions

1992

Abstract We quantize the closed Friedmann model in 2 + 1 spacetime dimensions using euclidean path-integral approach and a simple microsuperspace model. A relationship between integration measure and operator ordering in the Wheeler-DeWitt equation is found within our model. Solutions to the Wheeler-DeWitt equation are exactly reproduced from the path integral using suitable integration contours in the complex plane.

Geometric operators in the asymptotic safety scenario for quantum gravity

2019

We consider geometric operators, such as the geodesic length and the volume of hypersurfaces, in the context of the Asymptotic Safety scenario for quantum gravity. We discuss the role of these operators from the Asymptotic Safety perspective, and compute their anomalous dimensions within the Einstein-Hilbert truncation. We also discuss certain subtleties arising in the definition of such geometric operators. Our results hint to an effective dimensional reduction of the considered geometric operators.

Post-Newtonian constraints onf(R)cosmologies in metric and Palatini formalism

2005

We compute the complete post-Newtonian limit of both the metric and Palatini formulations of $f(R)$ gravities using a scalar-tensor representation. By comparing the predictions of these theories with laboratory and solar system experiments, we find a set of inequalities that any lagrangian $f(R)$ must satisfy. The constraints imposed by those inequalities allow us to find explicit bounds to the possible nonlinear terms of the lagrangian. We conclude that in both formalisms the lagrangian $f(R)$ must be almost linear in $R$ and that corrections that grow at low curvatures are incompatible with observations. This result shows that modifications of gravity at very low cosmic densities cannot b…

(2+1)-dimensional Einstein-Kepler problem in the centre-of-mass frame

1999

We formulate and analyze the Hamiltonian dynamics of a pair of massive spinless point particles in (2+1)-dimensional Einstein gravity by anchoring the system to a conical infinity, isometric to the infinity generated by a single massive but possibly spinning particle. The reduced phase space \Gamma_{red} has dimension four and topology R^3 x S^1. \Gamma_{red} is analogous to the phase space of a Newtonian two-body system in the centre-of-mass frame, and we find on \Gamma_{red} a canonical chart that makes this analogue explicit and reduces to the Newtonian chart in the appropriate limit. Prospects for quantization are commented on.

One-Dimensional Diffusion

2009

Effect of spin on the inspiral of binary neutron stars

2019

We perform long-term simulations of spinning binary neutron stars, with our highest dimensionless spin being $\chi \sim 0.32$. To assess the importance of spin during the inspiral we vary the spin, and also use two equations of state, one that consists of plain nuclear matter and produces compact stars (SLy), and a hybrid one that contains both nuclear and quark matter and leads to larger stars (ALF2). Using high resolution that has grid spacing $\Delta x\sim 98$ m on the finest refinement level, we find that the effects of spin in the phase evolution of a binary system can be larger than the one that comes from tidal forces. Our calculations demonstrate explicitly that although tidal effec…