Search results for "massless"
showing 10 items of 191 documents
Effect of low mass dark matter particles on the Sun
2010
We study the effect of dark matter (DM) particles in the Sun, focusing in particular on the possible reduction of the solar neutrinos flux due to the energy carried away by DM particles from the innermost regions of the Sun, and to the consequent reduction of the temperature of the solar core. We find that in the very low-mass range between 4 and 10 GeV, recently advocated to explain the findings of the DAMA and CoGent experiments, the effects on neutrino fluxes are detectable only for DM models with very small, or vanishing, self-annihilation cross section, such as the so-called asymmetric DM models, and we study the combination of DM masses and Spin Dependent cross sections which can be e…
A Wilson-Yukawa Model with undoubled chiral fermions in 2D
1997
We consider the fermion spectrum in the strong coupling vortex phase of a lattice fermion-scalar model with a global $U(1)_L\times U(1)_R$, in 2D, in the context of a recently proposed two-cutoff lattice formulation. The fermion doublers are made massive by a strong Wilson-Yukawa coupling, but in contrast with the standard formulation of these models, in which the light fermion spectrum was found to be massive and vectorlike, we find massless undoubled fermions with chiral quantum numbers at finite lattice spacing. When the global symmetry is gauged, this model is expected to give rise to a chiral gauge theory.
Massless Spectra and Gauge Couplings at One-Loop on Non-Factorisable Toroidal Orientifolds
2018
So-called `non-factorisable' toroidal orbifolds can be rewritten in a factorised form as a product of three two-tori by imposing an additional shift symmetry. This finding of Blaszczyk et al., arXiv:1111.5852, provides a new avenue to Conformal Field Theory methods, by which the vector-like massless matter spectrum - and thereby the type of gauge group enhancement on orientifold invariant fractional D6-branes - and the one-loop corrections to the gauge couplings in Type IIA orientifold theories can be computed in addition to the well-established chiral matter spectrum derived from topological intersection numbers among three-cycles. We demonstrate this framework for the $\mathbb{Z}_4 \times…
Bounds on Neutrino-Scalar Yukawa Coupling
2015
General neutrino-scalar couplings appear in many extensions of Standard Model. We can probe these neutrino-scalar couplings by leptonic decay of mesons and from heavy neutrino search. Our analysis improves the present limits to $|g_e|^2<1.9\times 10^{-6}$ and $|g_\mu|^2<1.9\times 10^{-7}$ at 90\% C.L. for massless scalars. For massive scalars we found for the first time the constraints for $g^2_{\alpha}$ couplings to be $10^{-6}-10^{-1}$ respectively for scalar masses between below 1 MeV and for 300 MeV.
Energy-level shifts of a uniformly accelerated atom between two reflecting plates
2011
We discuss the radiative level shifts of a uniformly accelerated atom moving between two infinite reflecting plates and interacting with a massless scalar field in the vacuum state. The atom, supposed to be a two-level system, accelerates in a direction parallel to the conducting plates. We evaluate separately the contributions of vacuum fluctuations and radiation reaction field to the energy shift of the atomic levels, and discuss their dependence on acceleration, atomic position and cavity length.
Probing New Long-Range Interactions by Isotope Shift Spectroscopy
2018
We explore a method to probe new long- and intermediate-range interactions using precision atomic isotope shift spectroscopy. We develop a formalism to interpret linear King plots as bounds on new physics with minimal theory inputs. We focus only on bounding the new physics contributions that can be calculated independently of the standard model nuclear effects. We apply our method to existing Ca[superscript +] data and project its sensitivity to conjectured new bosons with spin-independent couplings to the electron and the neutron using narrow transitions in other atoms and ions, specifically, Sr and Yb. Future measurements are expected to improve the relative precision by 5 orders of magn…
Four-gluon scattering at three loops, infrared structure and Regge limit
2016
We compute the three-loop four-gluon scattering amplitude in maximally supersymmetric Yang-Mills theory, including its full color dependence. Our result is the first complete computation of a non-planar four-particle scattering amplitude to three loops in four-dimensional gauge theory and consequently provides highly non-trivial data for the study of non-planar scattering amplitudes. We present the amplitude as a Laurent expansion in the dimensional regulator to finite order, with coefficients composed of harmonic poly-logarithms of uniform transcendental weight, and simple rational prefactors. Our computation provides an independent check of a recent result for three-loop corrections to th…
Schwinger mechanism in linear covariant gauges
2016
In this work we explore the applicability of a special gluon mass generating mechanism in the context of the linear covariant gauges. In particular, the implementation of the Schwinger mechanism in pure Yang-Mills theories hinges crucially on the inclusion of massless bound-state excitations in the fundamental nonperturbative vertices of the theory. The dynamical formation of such excitations is controlled by a homogeneous linear Bethe-Salpeter equation, whose nontrivial solutions have been studied only in the Landau gauge. Here, the form of this integral equation is derived for general values of the gauge-fixing parameter, under a number of simplifying assumptions that reduce the degree of…
Conformal Symmetry and Feynman Integrals
2018
Singularities hidden in the collinear region around an external massless leg may lead to conformal symmetry breaking in otherwise conformally invariant finite loop momentum integrals. For an $\ell$-loop integral, this mechanism leads to a set of linear $2$nd-order differential equations with a non-homogeneous part. The latter, due to the contact nature of the anomaly in momentum space, is determined by $(\ell-1)$-loop information. Solving such differential equations in general is an open problem. In the case of 5-particle amplitudes up to two loops, the function space is known, and we can thus follow a bootstrap approach to write down the solution. As a first application of this method, we …
Nonequilibrium dressing in a cavity with a movable reflecting mirror
2017
We consider a movable mirror coupled to a one-dimensional massless scalar field in a cavity. Both the field and the mirror's mechanical degrees of freedom are described quantum-mechanically, and they can interact each other via the radiation pressure operator. We investigate the dynamical evolution of mirror and field starting from a nonequilibrium initial state, and their local interaction which brings the system to a stationary configuration for long times. This allows us to study the time-dependent dressing process of the movable mirror interacting with the field, and its dynamics leading to a local equilibrium dressed configuration. Also, in order to explore the effect of the radiation …