arXiv subjects

Celine Boehm

Publications and source records attributed to Celine Boehm.

At least 37 records · Page 2Linked to original sources

arXiv2021

Optical reconstruction of dust in the region of SNR RX J1713.7-3946 from astrometric data

The origin of the radiation observed in the region of the supernova remnant RX J1713.7-3946, one of the brightest TeV emitters, has been debated since its discovery. The existence of atomic and molecular clouds in this object supports the idea that part of the GeV gamma rays in this region originate from proton-proton collisions. However, the observed column density of protons derived from gas observations cannot explain the whole emission. Yet there could be a fraction of protons contained in fainter structures that have note been detected so far. Here we search for faint objects in the line of sight of RX J1713.7-3946 using the principle of light extinction and the ESA/Gaia DR2 astrometric and photometric data. We reveal and locate with precision a number of dust clouds and note that only one appears to be in the vicinity of RX J1713.7-3946. We estimate the embedded mass to $M_{dust} = (7.0 \pm 0.6) \times 10^3 \, M_{\odot}$ which might be big enough to contain the missing protons. Finally, using the fact that the supernova remnant is expected to be located in a dusty environment and that there appears to be only one such structure in the vicinity of RX J1713.7-3946, we set a very precise constrain to the supernova remnant distance, at ($1.12 \pm 0.01$) kpc.

astro-ph.HE↗

arXiv2020

The full Boltzmann hierarchy for dark matter-massive neutrino interactions

The impact of dark matter-neutrino interactions on the measurement of the cosmological parameters has been investigated in the past in the context of massless neutrinos exclusively. Here we revisit the role of a neutrino-dark matter coupling in light of ongoing cosmological tensions by implementing the full Boltzmann hierarchy for three massive neutrinos. Our tightest 95% CL upper limit on the strength of the interactions, parameterized via $u_χ=\frac{σ_0}{σ_{Th}}\left(\frac{m_χ}{100 \text{GeV}}\right)^{-1}$, is $u_χ\leq3.34 \cdot 10^{-4}$, arising from a combination of Planck TTTEEE data, Planck lensing data and SDSS BAO data. This upper bound is, as expected, slightly higher than previous results for interacting massless neutrinos, due to the correction factor associated with neutrino masses. We find that these interactions significantly relax the lower bounds on the value of $σ_8$ that is inferred in the context of $Λ$CDM from the Planck data, leading to agreement within 1-2$σ$ with weak lensing estimates of $σ_8$, as those from KiDS-1000. However, the presence of these interactions barely affects the value of the Hubble constant $H_0$.

astro-ph.CO↗

arXiv2020

The BUFFALO HST Survey

The Beyond Ultra-deep Frontier Fields and Legacy Observations (BUFFALO) is a 101 orbit + 101 parallel Cycle 25 Hubble Space Telescope Treasury program taking data from 2018-2020. BUFFALO will expand existing coverage of the Hubble Frontier Fields (HFF) in WFC3/IR F105W, F125W, and F160W and ACS/WFC F606W and F814W around each of the six HFF clusters and flanking fields. This additional area has not been observed by HST but is already covered by deep multi-wavelength datasets, including Spitzer and Chandra. As with the original HFF program, BUFFALO is designed to take advantage of gravitational lensing from massive clusters to simultaneously find high-redshift galaxies which would otherwise lie below HST detection limits and model foreground clusters to study properties of dark matter and galaxy assembly. The expanded area will provide a first opportunity to study both cosmic variance at high redshift and galaxy assembly in the outskirts of the large HFF clusters. Five additional orbits are reserved for transient followup. BUFFALO data including mosaics, value-added catalogs and cluster mass distribution models will be released via MAST on a regular basis, as the observations and analysis are completed for the six individual clusters.

astro-ph.GA↗

arXiv2020

Polarisation of high energy gamma-rays after scattering

The polarisation of sunlight after scattering off the atmosphere was first described by Chandrasekhar using a geometrical description of Rayleigh interactions. Kosowsky later extended Chandrasekhar's formalism by using Quantum Field Theory (QFT) to describe the polarisation of the Cosmological Microwave Background radiation. Here we focus on a case that is rarely discussed in the literature, namely the polarisation of high energy radiation after scattering off particles. After demonstrating why the geometrical and low energy QFT approaches fail in this case, we establish the transport formalism that allows to describe the change of polarisation of high energy photons when they propagate through space or the atmosphere. We primarily focus on Compton interactions but our approach is general enough to describe e.g. the scattering of high energy photons off new particles or through new interactions. Finally we determine the conditions for a circularly polarised $γ$--ray signal to keep the same level of circular polarisation as it propagates through its environment.

hep-ph↗

arXiv2019

Reply to a comment on `Understanding the gamma-ray emission from the globular cluster 47 Tuc: evidence for dark matter?'

Analysing 9 years of Fermi-LAT observations, we recently studied the spectral properties of the prominent globular cluster 47 Tuc (Brown et al. 2018). In particular, we investigated several models to explain the observed gamma-ray emission, ranging from millisecond pulsars (MSP) to Dark Matter (DM), with the motivation for the latter model driven by recent evidence that 47 Tuc harbours an intermediate-mass black hole (IMBH). This investigation found evidence that the observed gamma-ray emission from 47 Tuc is due to two source populations of MSPs and DM. In Bartels \& Edwards (2018), the authors comment that this evidence is an artifact of the MSP spectra used in (Brown et al. 2019). Here we reply to this comment and argue that the authors of Bartels \& Edwards (2018) (i) do not give due consideration to a very important implication of their result and (ii) there is tension between our MSP fit and their MSP fit when taking uncertainties into consideration. As such, we still conclude there is evidence for a DM component which motivates a deeper radio study of the prominent globular cluster 47 Tuc.

astro-ph.HE↗

arXiv2019

All-Sky Near Infrared Space Astrometry

Gaia is currently revolutionizing modern astronomy. However, much of the Galactic plane, center and the spiral arm regions are obscured by interstellar extinction, rendering them inaccessible because Gaia is an optical instrument. An all-sky near infrared (NIR) space observatory operating in the optical NIR, separated in time from the original Gaia would provide microarcsecond NIR astrometry and millimag photometry to penetrate obscured regions unraveling the internal dynamics of the Galaxy.

astro-ph.IM↗

arXiv2019

Cosmological Probes of Dark Matter Interactions: The Next Decade

Cosmological observations offer unique and robust avenues for probing the fundamental nature of dark matter particles-they broadly test a range of compelling theoretical scenarios, often surpassing or complementing the reach of terrestrial and other experiments. We discuss observational and theoretical advancements that will play a pivotal role in realizing a strong program of cosmological searches for the identity of dark matter in the coming decade. Specifically, we focus on measurements of the cosmic-microwave-background anisotropy and spectral distortions, and tracers of structure (such as the Lyman-$α$ forest, galaxies, and the cosmological 21-cm signal).

astro-ph.CO↗

arXiv2018

Precision Space Astrometry as a Tool to Find Earth-like Exoplanets

Because of the recent technological advances, the key technologies needed for precision space optical astrometry are now in hand. The Microarcsecond Astrometry Probe (MAP) mission concept is designed to find 1 Earth mass planets at 1AU orbit (scaled to solar luminosity) around the nearest ~90 FGK stars. The MAP payload includes i) a single three-mirror anastigmatic telescope with a 1-m primary mirror and metrology subsystems, and ii) a camera. The camera focal plane consists of 42 detectors, providing a Nyquist sampled FOV of 0.4-deg. Its metrology subsystems ensure that MAP can achieve the 0.8 uas astrometric precision in 1 hr, which is required to detect Earth-like exoplanets in our stellar neighborhood. MAP mission could provide ~10 specific targets for a much larger coronagraphic mission that would measure its spectra. We argue for the development of the space astrometric missions capable of finding Earth-2.0. Given the current technology readiness such missions relying on precision astrometry could be flown in the next decade, perhaps in collaboration with other national space agencies.

astro-ph.IM↗

arXiv2018

Unique probe of dark matter in the core of M87 with the Event Horizon Telescope

We demonstrate the unprecedented capabilities of the Event Horizon Telescope (EHT) to image the innermost dark matter profile in the vicinity of the supermassive black hole at the center of the M87 radio galaxy. We present the first model of the synchrotron emission induced by dark matter annihilations from a spiky profile in the close vicinity of a supermassive black hole, accounting for strong gravitational lensing effects. Our results show that the EHT should readily resolve dark matter spikes if present. Moreover, the photon ring surrounding the silhouette of the black hole is clearly visible in the spike emission, which introduces observable small-scale structure into the signal. We find that the dark matter-induced emission provides an adequate fit to the existing EHT data, implying that in addition to the jet, a dark matter spike may account for a sizable portion of the millimeter emission from the innermost (subparsec) region of M87. Regardless, our results show that the EHT can probe very weakly annihilating dark matter. Current EHT observations already constrain very small cross sections, typically down to a few 10^{-31} cm^{3} s^{-1} for a 10 GeV candidate, close to characteristic values for p-wave-suppressed annihilation. Future EHT observations will further improve constraints on the DM scenario.

astro-ph.GA↗

arXiv2017

Exploring dark matter microphysics with galaxy surveys

We use present cosmological observations and forecasts of future experiments to illustrate the power of large-scale structure (LSS) surveys in probing dark matter (DM) microphysics and unveiling potential deviations from the standard $Λ$CDM scenario. To quantify this statement, we focus on an extension of $Λ$CDM with DM-neutrino scattering, which leaves a distinctive imprint on the angular and matter power spectra. After finding that future CMB experiments (such as COrE+) will not significantly improve the constraints set by the Planck satellite, we show that the next generation of galaxy clustering surveys (such as DESI) could play a leading role in constraining alternative cosmologies and even have the potential to make a discovery. Typically we find that DESI would be an order of magnitude more sensitive to DM interactions than Planck, thus probing effects that until now have only been accessible via $N$-body simulations.

astro-ph.CO↗

arXiv2017

Dark matter-neutrino interactions through the lens of their cosmological implications

Dark matter and neutrinos provide the two most compelling pieces of evidence for new physics beyond the Standard Model of Particle Physics but they are often treated as two different sectors. The aim of this paper is to determine whether there are viable particle physics frameworks in which dark matter can be coupled to active neutrinos. We use a simplified model approach to determine all possible renormalizable scenarios where there is such a coupling, and study their astrophysical and cosmological signatures. We find that dark matter-neutrino interactions have an impact on structure formation and lead to indirect detection signatures when the coupling between dark matter and neutrinos is sufficiently large. This can be used to exclude a large fraction of the parameter space. In most cases, dark matter masses up to a few MeV and mediator masses up to a few GeV are ruled out. The exclusion region can be further extended when dark matter is coupled to a spin-1 mediator or when the dark matter particle and the mediator are degenerate in mass if the mediator is a spin-0 or spin-1/2 particle.

hep-ph↗

arXiv2017

Future Astrometric Space Missions for Exoplanet Science

High-precision astrometry at the sub-microarcsecond level opens up a window to study Earth-like planets in the habitable zones of Sun-like stars, and to determine their masses. It thus promises to play an important role in exoplanet science in the future. However, such precision can only be acquired from space, and requires dedicated instrumentation for a sufficient astrometric calibration. Here we present a series of concepts designed for handling this task. STARE is a small satellite concept dedicated to finding planets in the very nearest stellar systems, which offers a low-cost option toward the study of habitable planets. The NEAT concept is a set of two formation-flying satellites with the aim to survey the 200 nearest Sun-like stars for Earths in the habitable zone. Finally, THEIA is a proposal for an ESA M-class mission, with a single-unit telescope designed for both dark matter studies as well as a survey for habitable Earth-like planets among the 50 nearest stars. The concepts illustrate various possible paths and strategies for achieving exquisite astrometric performance, and thereby addressing key scientific questions regarding the distribution of habitability and life in the universe.

astro-ph.EP↗

arXiv2017

Theia: Faint objects in motion or the new astrometry frontier

In the context of the ESA M5 (medium mission) call we proposed a new satellite mission, Theia, based on relative astrometry and extreme precision to study the motion of very faint objects in the Universe. Theia is primarily designed to study the local dark matter properties, the existence of Earth-like exoplanets in our nearest star systems and the physics of compact objects. Furthermore, about 15 $\%$ of the mission time was dedicated to an open observatory for the wider community to propose complementary science cases. With its unique metrology system and "point and stare" strategy, Theia's precision would have reached the sub micro-arcsecond level. This is about 1000 times better than ESA/Gaia's accuracy for the brightest objects and represents a factor 10-30 improvement for the faintest stars (depending on the exact observational program). In the version submitted to ESA, we proposed an optical (350-1000nm) on-axis TMA telescope. Due to ESA Technology readiness level, the camera's focal plane would have been made of CCD detectors but we anticipated an upgrade with CMOS detectors. Photometric measurements would have been performed during slew time and stabilisation phases needed for reaching the required astrometric precision.

astro-ph.IM↗

arXiv2017

Circular polarisation: a new probe of dark matter and neutrinos in the sky

The study of anomalous electromagnetic emission in the sky is the basis of indirect searches for dark matter. It is also a powerful tool to constrain the radiative decay of active neutrinos. Until now, quantitative analyses have focused on the flux and energy spectrum of such an emission; polarisation has never been considered. Here we show that we could be missing out on an essential piece of information. The radiative decay of neutrinos, as well as the interactions of dark matter and neutrinos with Standard Model particles can generate a circular polarisation signal in X-rays or γ-rays. If observed, this could reveal important information about their spatial distribution and particle-antiparticle ratio, and could even reveal the nature of the high-energy particle physics processes taking place in astrophysical sites. The question of the observability of these polarised signatures and their separation from background astrophysical sources is left for future work.

hep-ph↗

arXiv2017

Phenomenology of a Neutrino-DM Coupling: The Scalar Case

Dark matter (DM) and neutrinos are the two most compelling pieces of evidence of new physics beyond the Standard Model of Particle Physics but these are often treated as belonging to two different sectors. Yet DM-neutrino interactions are known to have cosmological consequences. Here, we study the scenario of a scalar DM candidate coupled to left-handed neutrinos via a Dirac mediator. We determine the mass of a DM candidate that yields the right DM relic abundance in a thermal scenario and it is consistent with large-scale structure formation. In order to satisfy both constraints, a complex DM candidate should have a mass larger than $8.14$ keV while the mass of a real DM candidate should be above $18.1$ eV, independently of the value of the DM-neutrino coupling.

hep-ph↗

arXiv2017

Connecting the new H.E.S.S. diffuse emission at the Galactic center with the Fermi GeV excess: a combination of millisecond pulsars and heavy dark matter?

The H.E.S.S. collaboration has reported a high-energy spherically symmetric diffuse gamma-ray emission in the inner 50 pc of the Milky Way, up to ~ 50 TeV. Here we propose a leptonic model which provides an alternative to the hadronic scenario presented by the H.E.S.S. collaboration, and connects the newly reported TeV emission to the Fermi-LAT Galactic center GeV excess. Our model relies on a combination of inverse Compton emission from a population of millisecond pulsars---which can account for the GeV excess---and a supermassive black hole-induced spike of heavy (~ 60 TeV) dark matter particles annihilating into electrons with a sub-thermal cross-section. With an up-to-date interstellar radiation field, as well as a standard magnetic field and diffusion set-up, our model accounts for the spectral morphology of the detected emission. Moreover, we show that the dark matter induced emission reproduces the spatial morphology of the H.E.S.S. signal above ~ 10 TeV, while we obtain a slightly more extended component from pulsars at lower energies, which could be used as a prediction for future H.E.S.S. observations.

astro-ph.HE↗

arXiv2016

Ruling out the light WIMP explanation of the galactic 511 keV line

Over the past few decades, an anomalous 511 keV gamma-ray line has been observed from the centre of the Milky Way. Dark matter (DM) in the form of light weakly interacting massive particles (WIMPs) annihilating into electron-positron pairs has been one of the leading hypotheses of the observed emission. Given the small required cross section, a further coupling to lighter particles is required to produce the correct relic density. Here, we derive constraints from the Planck satellite on light WIMPs that were in equilibrium with either the neutrino or electron sector in the early universe. For the neutrino sector, we obtain a lower bound on the WIMP mass of 4 MeV for a real scalar and 10 MeV for a Dirac fermion DM particle, at 95% CL. For the electron sector, we find even stronger bounds of 7 and 11 MeV, respectively. Using these results, we show that, in the absence of additional ingredients such as dark radiation, the light thermally produced WIMP explanation of the 511 keV excess is strongly disfavoured by the latest cosmological data. This suggests an unknown astrophysical or more exotic DM source of the signal.

astro-ph.CO↗

arXiv2016

Dark Sectors 2016 Workshop: Community Report

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years.

hep-ph↗