David Radice, Albino Perego, Francesco Zappa

Gravitational waves detected from the binary neutron star (NS) merger GW170817 constrained the NS equation of state by placing an upper bound on certain parameters describing the binary's tidal interactions. We show that the interpretation of the UV/optical/infrared counterpart of GW170817 with kilonova models, combined with new numerical relativity results, imply a complementary lower bound on the tidal deformability parameter. The joint constraints tentatively rule out both extremely stiff and soft NS equations of state.

Antony Lewis, Alex Hall, Anthony Challinor

Lensing of the CMB is an important effect, and is usually modelled by remapping the unlensed CMB fields by a lensing deflection. However the lensing deflections also change the photon path so that the emission angle is no longer orthogonal to the background last-scattering surface. We give the first calculation of the emission-angle corrections to the standard lensing approximation from dipole (Doppler) sources for temperature and quadrupole sources for temperature and polarization. We show that while the corrections are negligible for the temperature and E-mode polarization, additional large-scale B-modes are produced with a white spectrum that dominates those from post-Born field rotation (curl lensing). On large scales about one percent of the total lensing-induced B-mode amplitude is expected to be due to this effect. However, the photon emission angle does remain orthogonal to the perturbed last-scattering surface due to time delay, and half of the large-scale emission-angle B modes cancel with B modes from time delay to give a total contribution of about half a percent. While not important for planned observations, the signal could ultimately limit the ability of delensing to reveal low amplitudes of primordial gravitational waves.We also derive the rotation of polarization due to multiple deflections between emission and observation. The rotation angle is of quadratic order in the deflection angle, and hence negligibly small: polarization typically rotates by less than an arcsecond, orders of magnitude less than a small-scale image rotates due to post-Born field rotation (which is quadratic in the shear). The field-rotation B modes dominate the other effects on small scales.

jtd55

https://arxiv.org/new#nov13_2017

13 Nov 2017

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Nathan Moynihan, Jeff Murugan

Armed with the latest technology in the computation of scattering amplitudes involving massive particles of any spin, we revisit the van Dam-Veltman-Zakharov (vDVZ) discontinuity of massive gravity and show how it may be understood in terms of the Britto-Cachazo-Feng-Witten (BCFW) relations.

Boryana Hadzhiyska, David Spergel, Joanna Dunkley

Calculations of the Cosmic Microwave Background lensing power implemented into the standard cosmological codes such as CAMB and CLASS usually treat the surface of last scatter as an infinitely thin screen. However, since the CMB anisotropies are smoothed out on scales smaller than the diffusion length due to the effect of Silk damping, the photons which carry information about the small-scale density distribution come from slightly earlier times than the standard recombination time. The dominant effect is the scale dependence of the mean redshift associated with the fluctuations during recombination. We find that fluctuations at $k = 0.01 {\rm \ Mpc^{-1}}$ come from a characteristic redshift of $z \approx 1090$, while fluctuations at $k = 1 {\rm \ Mpc^{-1}}$ come from a characteristic redshift of $z \approx 1200$. We then estimate the corrections to the lensing kernel due to the finite size of the thickness of the surface of last scatter. We conclude that neglecting it would result in a deviation from the true value of the lensing kernel at the half percent level at small scales. For future high signal-to-noise CMB experiments (e.g., CMB-S4), this corresponds to a $\sim 0.3 \sigma$ shift on scales $k \sim 1 {\rm \ Mpc^{-1}}$.

Yevgeny V. Stadnik

The exchange of a pair of low-mass neutrinos between electrons, protons and neutrons produces a "long-range" $1/r^5$ potential, which can be sought for in phenomena originating on the atomic and nuclear scales. We calculate the effects of neutrino-pair exchange on transition and binding energies in atoms and nuclei. In the case of atomic $s$-wave states, there is a particularly large enhancement of the induced energy shifts due to the lack of a centrifugal barrier and the highly singular nature of the neutrino-mediated potential. We derive limits on neutrino-mediated forces from measurements of the deuteron binding energy and transition energies in positronium, muonium, hydrogen and deuterium, as well as isotope-shift measurements in calcium ions. Our limits improve on existing constraints on neutrino-mediated forces from experiments that search for new macroscopic forces by 18 orders of magnitude. Future spectroscopy experiments have the potential to probe long-range forces mediated by the exchange of pairs of standard-model neutrinos and other weakly-charged particles.