Search results for "GRAVITATION"

Gravitational wave probes of axionlike particles

2020

We have recently shown that axions and axion-like particles (ALPs) may emit an observable stochastic gravitational wave (GW) background when they begin to oscillate in the early universe. In this note, we identify the regions of ALP parameter space which may be probed by future GW detectors, including ground- and space-based interferometers and pulsar timing arrays. Interestingly, these experiments have the ability to probe axions from the bottom up, i.e. in the very weakly coupled regime which is otherwise unconstrained. Furthermore, we discuss the effects of finite dark photon mass and kinetic mixing on the mechanism, as well as the (in)sensitivity to couplings of the axion to Standard Mo…

Neutrino Spin Oscillations in External Gravitational Fields

2007

Triangle singularity enhancing isospin violation in $D_s^ + \to {\pi ^ + }{\pi ^0}{f_0}(980)$ and $\overline B _s^0 \to J/\psi {\pi ^0}{f_0}(980)$ de…

2019

We investigate isospin violation in the and reactions, which proceed via a triangle mechanism. We show that the mechanism develops a singularity around the π 0 f 0 (980) or π 0 a0 (980) invariant mass of 1420 MeV where the π 0 f 0 and π 0 a0 decay modes are magnified and also the ratio of π 0 f0 to π 0 a0 production, stressing the role of the triangle singularities as a factor to enhance isospin violation. The measurement of these reactions would bring further information into the role of triangle singularities in isospin violation and the a 0 – f 0 mixing in particular and shed further light into the nature of the low lying scalar mesons.

Calculation of theO(? s 2 ) parity-violating structure functions in $$e^ + e^ - \to q\bar qg$$

1986

We calculate the two nonvanishingO(αs2) parity-violating structure functions that contribute to\(e^ + e^ - \xrightarrow{{\gamma ,Z}}q\bar qg\). We discuss how these can be measured. We work with massless quarks and gluons and use dimensional regularization to regularize ultra-violet and infrared singularities. We carefully discuss how to deal withγ5 in the dimensional regularization scheme when infrared singularities are present.

Study of the possible role of triangle singularities in ${B^ - }\, \to {D^{*0}}{\pi ^ - }{\pi ^0}\eta $ and ${B^ - }\, \to {D^{*0}}{\pi ^ - }{\pi ^ +…

2019

Studying the effects of triangle singularities in hadronic processes is of the utmost importance since they can originate peaks that may wrongfully be associated with resonances. In this work, the role of the triangle mechanism in the decays and is explored. Here, the singularity appears when B- decays into , K *0 decays into K + through pion emission, and K - K + fuse together forming either the a 0 (980) or f 0 (980) which then decays into π 0 η or π+ π – , respectively. As a result, the K * K + K - loop generates a peak in the invariant mass of π - a 0 or π - f 0 around 1420 MeV. The branching ratios that come from this peak are and , which are well within the measurable range. Thus, thi…

Deforming D-brane models on T6/(Z2×Z2M) orbifolds

2016

We review the stabilisation of complex structure moduli in Type IIA orientifolds, especially on with discrete torsion, via deformations of orbifold singularities. While D6-branes in SO(2N) and USp(2N) models always preserve supersymmetry and thus give rise to flat directions, in an exemplary Pati-Salam model with only U(N) gauge groups ten out of the 15 deformation moduli can be stabilised at the orbifold point.

Exact non-Hookean scaling of cylindrically bent elastic sheets and the large-amplitude pendulum

2010

A sheet of elastic foil rolled into a cylinder and deformed between two parallel plates acts as a non-Hookean spring if deformed normally to the axis. For large deformations the elastic force shows an interesting inverse squares dependence on the interplate distance [Siber and Buljan, arXiv:1007.4699 (2010)]. The phenomenon has been used as a basis for an experimental problem at the 41st International Physics Olympiad. We show that the corresponding variational problem for the equilibrium energy of the deformed cylinder is equivalent to a minimum action description of a simple gravitational pendulum with an amplitude of 90 degrees. We use this analogy to show that the power-law of the force…

Electroweak baryogenesis at high bubble wall velocities

2020

It is widely believed that electroweak baryogenesis should be suppressed in strong phase transitions with fast-moving bubble walls, but this effect has never been quantitatively studied. We rederive fluid equations describing transport of particle asymmetries near the bubble wall without making the small-wall-velocity approximation. We show that the suppression of the baryon asymmetry is a smooth function of the wall speed and that there is no special behavior when crossing the sound speed barrier. Electroweak baryogenesis can thus be efficient also with strong detonations, generically associated with models with observably large gravitational waves. We also make a systematic and critical c…

Gravity and handedness of photons

2017

Vacuum fluctuations of quantum fields are altered in presence of a strong gravitational background, with important physical consequences. We argue that a non-trivial spacetime geometry can act as an optically active medium for quantum electromagnetic radiation, in such a way that the state of polarization of radiation changes in time, even in the absence of electromagnetic sources. This is a quantum effect, and is a consequence of an anomaly related to the classical invariance under electric-magnetic duality rotations in Maxwell theory.

Gravitational Waves from an Axion-Dark Photon System: A Lattice Study

2021

In this work, we present a lattice study of an axion - dark photon system in the early Universe and show that the stochastic gravitational wave (GW) background produced by this system may be probed by future GW experiments across a vast range of frequencies. The numerical simulation on the lattice allows us to take into account non-linear backreaction effects and enables us to accurately predict the final relic abundance of the axion or axion-like particle (ALP) as well as its inhomogeneities, and gives a more precise prediction of the GW spectrum. Importantly, we find that the GW spectrum has more power at high momenta due to $2\rightarrow1$ processes. Furthermore, we find the degree of po…