Lina Necib

New angles on energy correlation functions

A bstractJet substructure observables, designed to identify specific features within jets, play an essential role at the Large Hadron Collider (LHC), both for searching for signals beyond the Standard Model and for testing QCD in extreme phase space regions. In this paper, we systematically study the structure of infrared and collinear safe substructure observables, defining a generalization of the energy correlation functions to probe n-particle correlations within a jet. These generalized correlators provide a flexible basis for constructing new substructure observables optimized for specific purposes. Focusing on three major targets of the jet substructure community — boosted top tagging, boosted W/Z/H tagging, and quark/gluon discrimination — we use power-counting techniques to identify three new series of powerful discriminants: Mi, Ni, and Ui. The Mi series is designed for use on groomed jets, providing a novel example of observables with improved discrimination power after the removal of soft radiation. The Ni series behave parametrically like the N -subjettiness ratio observables, but are defined without respect to subjet axes, exhibiting improved behavior in the unresolved limit. Finally, the Ui series improves quark/gluon discrimination by using higher-point correlators to simultaneously probe multiple emissions within a jet. Taken together, these observables broaden the scope for jet substructure studies at the LHC.

Deciphering Contributions to the Extragalactic Gamma-Ray Background from 2 GeV to 2 TeV

Astrophysical sources outside the Milky Way, such as active galactic nuclei and star-forming galaxies, leave their imprint on the gamma-ray sky as nearly isotropic emission referred to as the Extragalactic Gamma-Ray Background (EGB). While the brightest of these sources may be individually resolved, their fainter counterparts contribute diffusely. In this work, we use a recently-developed analysis method, called the Non-Poissonian Template Fit, on up to 93 months of publicly-available data from the Fermi Large Area Telescope to determine the properties of the point sources that comprise the EGB. This analysis takes advantage of photon-count statistics to probe the aggregate properties of these source populations below the sensitivity threshold of published catalogs. We measure the source-count distributions and point-source intensities, as a function of energy, from 2 GeV to 2 TeV. We find that the EGB is dominated by point sources, likely blazars, in all seven energy sub-bins considered. These results have implications for the interpretation of IceCubes PeV neutrinos, which may originate from sources that contribute to the non-blazar component of the EGB. Additionally, we comment on implications for future TeV observatories such as the Cherenkov Telescope Array. We provide sky maps showing locations most likely to contain these new sources at both low ( 50 GeV) energies for use in future observations and cross-correlation studies.

Dark matter, shared asymmetries, and galactic gamma ray signals

We introduce a novel dark matter scenario where the visible sector and the dark sector share a common asymmetry. The two sectors are connected through an unstable mediator with baryon number one, allowing the standard model baryon asymmetry to be shared with dark matter via semi-annihilation. The present-day abundance of dark matter is then set by thermal freeze-out of this semi-annihilation process, yielding an asymmetric version of the WIMP miracle as well as promising signals for indirect detection experiments. As a proof of concept, we find a viable region of parameter space consistent with the observed Fermi excess of GeV gamma rays from the galactic center.

The metal-poor stellar halo in RAVE-TGAS and its implications for the velocity distribution of dark matter

The local velocity distribution of dark matter plays an integral role in interpreting the results from direct detection experiments. We previously showed that metal-poor halo stars serve as excellent tracers of the virialized dark matter velocity distribution using a high-resolution hydrodynamic simulation of a Milky Way--like halo. In this paper, we take advantage of the first \textit{Gaia} data release, coupled with spectroscopic measurements from the RAdial Velocity Experiment (RAVE), to study the kinematics of stars belonging to the metal-poor halo within an average distance of

Spherical cows in dark matter indirect detection

\sim 5

In)Direct detection of boosted dark matter

kpc of the Sun. We study stars with iron abundances [Fe/H]

In)direct Detection of Boosted Dark Matter

< -1.5

Empirical Determination of Dark Matter Velocities Using Metal-Poor Stars

and

Dark Matter in Disequilibrium: The Local Velocity Distribution from SDSS-Gaia

-1.8

Hunting for Point Sources in the Extragalactic Gamma-Ray Sky

that are located more than