Sterile neutrinos as subdominant warm dark matter

In light of recent findings which seem to disfavor a scenario with (warm) dark matter entirely constituted of sterile neutrinos produced via the Dodelson-Widrow (DW) mechanism, we investigate the constraints attainable for this mechanism by relaxing the usual hypothesis that the relic neutrino abundance must necessarily account for all of the dark matter. We first study how to reinterpret the limits attainable from X-ray non-detection and Lyman-alpha forest measurements in the case that sterile neutrinos constitute only a fraction fs of the total amount of dark matter. Then, assuming that sterile neutrinos are generated in the early universe solely through the DW mechanism, we show how the X-ray and Lyman-alpha results jointly constrain the mass-mixing parameters governing their production. Furthermore, we show how the same data allow us to set a robust upper limit fs < 0.7 at the 2 sigma level, rejecting the case of dominant dark matter (fs = 1) at the ~ 3 sigma level.Comment: Minor changes; added references; version accepted for publication in Phys. Rev.

B2 and G2 Toda systems on compact surfaces: a variational approach

We consider the B2 and G2 Toda systems on compact surfaces. We attack the problem using variational techniques. We get existence and multiplicity of solutions under a topological assumption on the surface and some generic conditions on the parameters. We also extend some of the results to the case of general systems.Comment: 28 pages, accepted on Journal of Mathematical Physic

The effect of tides on the Sculptor dwarf spheroidal galaxy

Dwarf spheroidal galaxies (dSphs) appear to be some of the most dark matter dominated objects in the Universe. Their dynamical masses are commonly derived using the kinematics of stars under the assumption of equilibrium. However, these objects are satellites of massive galaxies (e.g.\ the Milky Way) and thus can be influenced by their tidal fields. We investigate the implication of the assumption of equilibrium focusing on the Sculptor dSph by means of ad-hoc $N$-body simulations tuned to reproduce the observed properties of Sculptor following the evolution along some observationally motivated orbits in the Milky Way gravitational field. For this purpose, we used state-of-the-art spectroscopic and photometric samples of Sculptor's stars. We found that the stellar component of the simulated object is not directly influenced by the tidal field, while $\approx 30\%-60\%$ the mass of the more diffuse DM halo is stripped. We conclude that, considering the most recent estimate of the Sculptor proper motion, the system is not affected by the tides and the stellar kinematics represents a robust tracer of the internal dynamics. In the simulations that match the observed properties of Sculptor, the present-day dark-to-luminous mass ratio is $\approx 6$ within the stellar half-light radius ($\approx0.3$ kpc) and $>50$ within the maximum radius of the analysed dataset ($\approx1.5^\circ\approx2$ kpc).Comment: 19 pages, 10 figures, accepted for publication in MNRAS. V3: updated after editor comments See our playlist for simulation videos: https://av.tib.eu/series/633/supplemental+videos+of+the+paper+the+effect+of+tides+on+the+sculptor+dwarf+spheroidal+galax

Common-reflection-surface imaging of shallow and ultrashallow reflectors

We analyzed the feasibility of the common-reflection-surface (CRS) stack for near-surface surveys as an alternative to the conventional common midpoint (CMP) stacking procedure. The data-driven, less user-interactive CRS method could be more cost efficient for shallow surveys, where the high sensitivity to velocity analysis makes data processing a critical step. We compared the results for two field data sets collected to image shallow and ultrashallow reflectors: an example of shallow Pwave reflection for targets in the first few hundred meters, and an example of SH-wave reflection for targets in the first 10 m. By processing the shallow P-wave records using the CMP method, we imaged several nearly horizontal reflectors with onsets from 60 to about 250 ms. The CRS stack produced a stacked section more suited for a subsurface interpretation, without any preliminary formal and time-consuming velocity analysis, because the imaged reflectors possessed greater coherency and lateral continuity. With CMP processing of the SHwave records, we imaged a dipping bedrock interface below four horizontal reflectors in unconsolidated, very low velocity sediments. The vertical and lateral resolution was very high, despite the very shallow depth: the image showed the pinchout of two layers at less than 10 m depth. The numerous traces used by the CRS stack improved the continuity of the shallowest reflector, but the deepest overburden reflectors appear unresolved, with not well-imaged pinchouts. Using the kinematic wavefield attributes determined for each stacking operation, we retrieved velocity fields fitting the stacking velocities we had estimated in the CMP processing. The use of CRS stack could be a significant step ahead to increase the acceptance of the seismic reflection method as a routine investigation method in shallow and ultrashallow seismics

Exciting dark matter in the galactic center

We reconsider the proposal of excited dark matter (DM) as an explanation for excess 511 keV gamma rays from positrons in the galactic center. We quantitatively compute the cross section for DM annihilation to nearby excited states, mediated by exchange of a new light gauge boson with off-diagonal couplings to the DM states. In models where both excited states must be heavy enough to decay into e^+ e^- and the ground state, the predicted rate of positron production is never large enough to agree with observations, unless one makes extreme assumptions about the local circular velocity in the Milky Way, or alternatively if there exists a metastable population of DM states which can be excited through a mass gap of less than 650 keV, before decaying into electrons and positrons.Comment: Dedicated to the memory of Lev Kofman; 16 pages, 9 figures; v3 added refs, minor changes, accepted to PR

Gamma rays from ultracompact primordial dark matter minihalos

Ultracompact minihalos have recently been proposed as a new class of dark matter structure. These minihalos would be produced by phase transitions in the early Universe or features in the inflaton potential, and constitute non-baryonic massive compact halo objects (MACHOs) today. We examine the prospect of detecting ultracompact minihalos in gamma-rays if dark matter consists of self-annihilating particles. We compute present-day fluxes from minihalos produced in the electron-positron annihilation epoch, and the QCD and electroweak phase transitions in the early Universe. Even at a distance of 100 pc, minihalos produced during the electron-positron annihilation epoch should be eminently detectable today, either by the Fermi satellite, current Air Cherenkov telescopes, or even in archival EGRET data. Within ~1 pc, minihalos formed in the QCD phase transition would have similar predicted fluxes to the dwarf spheroidal galaxies targeted by current indirect dark matter searches, so might also be detectable by present or upcoming experiments.Comment: 5 pages, 3 figures. Minor update to match published version of erratu

Studies of New Vector Resonances at the CLIC Multi-TeV e+e- Collider

Several models predict the existence of new vector resonances in the multi-TeV region, which can be produced in high energy e+e- collisions in the s-channel. In this paper we review the existing limits on the masses of these resonances from LEP/SLC and TEVATRON data and from atomic parity violation in some specific models. We study the potential of a multi-TeV e+e- collider, such as CLIC, for the determination of their properties and nature.Comment: 17 pages, 16 EPS figures, uses JHEP3.cl

Bicycle Mobility in Glacier National Park: Assessing Going-to-the-Sun Road Travelers\u27 Attitudes, Knowledge, and Perceptions of Bicycling

The central aim of this thesis assessed whether Going-to-the-Sun Road (GTSR) travelers have a positive or negative association with roadway bicycling and the degree of public support for GTSR bicycling in Glacier National Park (GNP). Secondarily, this thesis tested a control and treatment group’s knowledge of roadway cycling laws to determine the effectiveness of a “Bicycles May Use Full Lane” sign and brochure, which both reflected Montana’s cycling laws. Finally, an analysis of the necessity of GNP’s partial bicycle restriction on the GTSR was conducted by comparing the characteristics of two road segments using GIS, and by assessing the attitudes, perceptions, and interactions occurring between travelers. Two approaches were used to assess bicycling mobility in GNP: (1) a quantitative analysis of travelers’ frequency of bicycling, attitudes, knowledge, and perceptions (2) and a geographical and mobilities framework to critically discuss the hierarchy of GTSR mobility. An onsite survey was conducted at Logan Pass in August to collect data from travelers based on their frequency with cycling, whether they cycled the GTSR or drove a motor vehicle, and whether or not they viewed an experimental treatment sign. A GIS was used to analyze two sections of the GTSR. This thesis challenges the assumption that a partial bicycling restriction is warranted based on the key findings reported. Despite travelers’ frequency of bicycling, they were primarily positive in the way they legitimize cyclists on the roadway, and the majority were neutral to positive in their support for unrestricted GTSR cycling. Respondents with knowledge of cycling laws showed more positive attitudes, and the sign/brochure treatments were effective at improving their knowledge of the cycling laws. Interactions between GTSR cyclists and motorists were overwhelmingly positive. Finally, the comparison of road segments suggests the restriction was implemented arbitrarily without empirical evidence. Automobility is prioritized over bicycling mobility to support steady tourism flows. By confronting power relations that prioritize auto-tourism, a re-produced tourism space can begin to occur along the Going-to-the-Sun Road. Glacier National Park is in a position to evaluate the data and critical discussion from this thesis to begin working towards greater mobility evenness

Excuse Me, Everybody

For my senior thesis I planned to write, produce, and direct a short-form, narrative film, entitled Excuse Me, Everybody. The original plot of the film is about a 19-year-old college student named Jacob who feels that his life is turned upside down after taking lewd photos of a fellow female student. While meeting with his psychotherapist, he refuses to reveal to him the true nature of his distress. He ultimately comes to terms with his crime by experiencing a hallucination where an imaginary being named Ego appears to him and forces Jacob to recollect the past events and explain his inner thoughts. As his conversation with Ego proceeds, Jacob wonders if he can ever redeem himself, or if he will continue to fall into a deeper, downward spiral. I was inspired to produce this film by some of television journalist Chris Hansen’s work, namely, To Catch a Predator and Hansen Vs. Predator as well as some other “predator catching” channels on YouTube that I watched for research and inspiration, such as Predator Poachers and Dads Against Predators. What I found interesting about these TV shows and videos was how the predators react at the moment of being caught. They start to change their emotions, begging and crying, and complaining that their lives and reputation are about to be ruined. Obviously, I don’t have much sympathy for these predators; however, from their perspective, it seems like an absolutely terrifying situation to experience. So, with Excuse Me Everybody, I wanted to delve into the psychology of a deviant person at the moment they realize they have been discovered and their entire life is ruined by their unscrupulous actions. For my film, I thought it would be interesting to condense the psychological trauma experienced by the perpetrator into a single, intense moment. I developed the original screenplay based on this concept and a copy of that script is included with this thesis submission. I also created storyboards based on this screenplay. The original intent was to produce a film that blended elements of psychological horror with dark comedy. Unfortunately, towards the end of the project, I ran into some major production issues with the original script, which forced me to significantly alter the premise and plot of the film. The final version of the film as shot ended up being a mockumentary/narrative of the events during the final weeks of production, where a young, aspiring filmmaker struggles with the difficulties in trying to complete his first major project