# Conformal Higgs Gravity [CL]

It is shown that gravitation emerges naturally from the standard model of particle physics if local scale invariance is imposed in the context of a single conformal theory. Doing so resolves major puzzles afflicting the standard models of particle physics and cosmology, clearly indicating these to be artifacts stemming from universally applying the system of units selected here and now. Slip-free scalar (but not vector or tensor) modes of metric perturbations can be gauged away and are thus spurious degrees of freedom. In the approach adopted here gravitation is viewed as a collective phenomenon, with its characteristic Planck scale devoid of fundamental meaning; consequently, mass hierarchy and Higgs mass instability concerns are avoided altogether. On cosmological scales, the dynamical vacuum-like Higgs self-coupling energy accounts for dark energy, and its near equality with nonrelativistic matter is simply a result of the choice of standard units.

M. Shimon
Tue, 12 Dec 17
10/78

# $ν$CO$N$CEPT: Cosmological neutrino simulations from the non-linear Boltzmann hierarchy [CEA]

In this paper the non-linear effect of massive neutrinos on cosmological structures is studied in a conceptually new way. We have solved the non-linear continuity and Euler equations for the neutrinos on a grid in real space in $N$-body simulations, and closed the Boltzmann hierarchy at the non-linear Euler equation using the stress and pressure perturbations from linear theory. By comparing with state-of-the art cosmological neutrino simulations, we are able to simulate the non-linear neutrino power spectrum very accurately. This translates into a negligible error in the matter power spectrum, and so our CONCEPT code is ideally suited for extracting the neutrino mass from future high precision non-linear observational probes such as Euclid.

J. Dakin, J. Brandbyge, S. Hannestad, et. al.
Tue, 12 Dec 17
11/78

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# Dark Matter as Ultralight Axion-Like particle in $E_6 \times U(1)_X$ GUT with QCD Axion [CL]

Axion-like fields are naturally generated by a mechanism of anomaly cancellation of one or more anomalous gauge abelian symmetries at the Planck scale, emerging as duals of a two-form from the massless bosonic sector of string theory. This suggests an analogy of the Green-Schwarz mechanism of anomaly cancellation, at field theory level, which results in one or more Stueckelberg pseudoscalars. In the case of a single Stueckelberg pseudoscalar $b$, vacuum misalignments at phase transitions in the early Universe at the GUT scale provide a small mass – due to instanton suppression of the periodic potential – for a component of $b$, denoted as $\chi$ and termed the “axi-Higgs”, which is a physical axion-like particle. The coupling of the axi-Higgs to the gauge sector via Wess-Zumino terms is suppressed by the Planck mass, which guarantees its decoupling, while its angle of misalignment is related to $M_{GUT}$. We build a gauged $E_6\times U(1)$ model with anomalous $U(1)$. It contains both an automatic invisible QCD axion and an ultra-light axi-Higgs. The invisible axion present in the model solves the strong CP problem and has mass in the conventional range while the axi-Higgs, which can act as dark matter, is sufficiently light ($10^{-22} \textrm{ eV} < m_{\chi} < 10^{-20} \textrm{ eV}$) to solve short-distance problems which confront other cold dark matter candidates.

C. Coriano and P. Frampton
Tue, 12 Dec 17
16/78

# Late time afterglow observations reveal a collimated relativistic jet in the ejecta of the binary neutron star merger GW170817 [HEAP]

The binary neutron star (BNS) merger GW170817 was the first astrophysical source detected in gravitational waves and multi-wavelength electromagnetic radiation. The almost simultaneous observation of a pulse of gamma-rays proved that BNS mergers are associated with at least some short gamma-ray bursts (GRBs). However, the gamma-ray pulse was faint, casting doubts on the association of BNS mergers with the luminous, highly relativistic outflows of canonical short GRBs. Here we show that structured jets with a relativistic, energetic core surrounded by slower and less energetic wings produce afterglow emission that brightens characteristically with time, as recently seen in the afterglow of GW170817. Initially, we only see the relatively slow material moving towards us. As time passes, larger and larger sections of the outflow become visible, increasing the luminosity of the afterglow. The late appearance and increasing brightness of the multi-wavelength afterglow of GW170817 allow us to constrain the geometry of its ejecta and thus reveal the presence of an off-axis jet pointing about 20 degrees away from Earth. Our results confirm a single origin for BNS mergers and short GRBs: GW170817 produced a structured outflow with a highly relativistic core and a canonical short GRB. We did not see the bright burst because it was beamed away from Earth. However, approximately one in 20 mergers detected in gravitational waves will be accompanied by a bright, canonical short GRB.

D. Lazzati, R. Perna, B. Morsony, et. al.
Tue, 12 Dec 17
19/78

Comments: 24 pages, 3 figures (main text), 7 figures (methods) and 1 table

# The Evens and Odds of CMB Anomalies [CEA]

The lack of power of large–angle CMB anisotropies is known to increase its statistical significance at higher Galactic latitudes, where a string–inspired pre–inflationary scale $\Delta$ can also be detected. Considering the Planck 2015 data, and relying largely on a Bayesian approach, a novelty for CMB anomalies, we show that the effect is mostly driven by the \emph{even}–$\ell$ harmonic multipoles with $\ell \lesssim 20$, which appear sizably suppressed in a way that is robust with respect to Galactic masking, along with the corresponding detections of $\Delta$. On the other hand, the first \emph{odd}–$\ell$ multipoles are only suppressed at high Galactic latitudes. We investigate this behavior in different sky masks, constraining $\Delta$ through even and odd multipoles, and we elaborate on possible implications. We include systematically low–$\ell$ polarization data, which are currently noise limited and yet help in attaining confidence levels of about 3 $\sigma$ in the detection of $\Delta$. We also show by direct forecasts that a future all–sky $E$–mode cosmic–variance–limited polarization survey may push the constraining power for $\Delta$ beyond 5 $\sigma$.

A. Gruppuso, N. Kitazawa, M. Lattanzi, et. al.
Tue, 12 Dec 17
25/78

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# Prospects of type-II seesaw at future colliders in light of the DAMPE $e^+ e^-$ excess [CL]

The DAMPE $e^+ e^-$ excess at around 1.4 TeV could be explained in the type-II seesaw model with a scalar dark mater $D$ which is stabilized by a discrete $Z_2$ symmetry. The simplest scenario is the annihilation $DD \to H^{++} H^{–}$ followed by the subsequent decay $H^{\pm\pm} \to e^\pm e^\pm$, with both the DM and triplet scalars roughly 3 TeV with a small mass splitting. In addition to the Drell-Yan process at future 100 TeV hadron colliders, the doubly-charged components could also be produced at lepton colliders like ILC and CLIC in the off-shell mode, and mediate lepton flavor violating processes $e^+ e^- \to \ell_i^\pm \ell_j^\mp$ (with $i \neq j$). A wide range of parameter space of the type-II seesaw could be probed, which are well below the current stringent lepton flavor constraints.

Y. Sui and Y. Zhang
Tue, 12 Dec 17
26/78