Aether Scalar Tensor (AeST) theory: Quasistatic spherical solutions and their phenomenology

There have been many efforts in the last three decades to embed the empirical MOND program into a robust theoretical framework. While many such theories can explain the profile of galactic rotation curves, they usually cannot explain the evolution 15 the primordial fluctuations and the formation of large-scale-structures in the Universe. The Aether Scalar Tensor (AeST) theory seems to have overcome this difficulty, thereby providing the first compelling example of an extension of general relativity able to successfully challenge the particle dark matter hypothesis. Here we study the phenomenology of this theory in the quasistatic weak-field regime and specifically for the idealised case of spherical isolated sources. We find the existence of three distinct gravitational regimes, that is, Newtonian, MOND and a third regime characterised by the presence of oscillations in the gravitational potential which do not exist in the traditional MOND paradigm. We identify the transition scales between these three regimes and discuss their dependence on the boundary conditions and other parameters in the theory. Aided by analytical and numerical solutions, we explore the dependence of these solutions on the theory parameters. Our results could help in searching for interesting observable phenomena at low redshift pertaining to galaxy dynamics as well as lensing observations, however, this may warrant proper N-body simulations that go beyond the idealised case of spherical isolated sources.Comment: 15 pages, 8 figure

The XENON100 exclusion limit without considering Leff as a nuisance parameter

In 2011, the XENON100 experiment has set unprecedented constraints on dark matter-nucleon interactions, excluding dark matter candidates with masses down to 6 GeV if the corresponding cross section is larger than 10^{-39} cm^2. The dependence of the exclusion limit in terms of the scintillation efficiency (Leff) has been debated at length. To overcome possible criticisms XENON100 performed an analysis in which Leff was considered as a nuisance parameter and its uncertainties were profiled out by using a Gaussian likelihood in which the mean value corresponds to the best fit Leff value smoothly extrapolated to zero below 3 keVnr. Although such a method seems fairly robust, it does not account for more extreme types of extrapolation nor does it enable to anticipate on how much the exclusion limit would vary if new data were to support a flat behaviour for Leff below 3 keVnr, for example. Yet, such a question is crucial for light dark matter models which are close to the published XENON100 limit. To answer this issue, we use a maximum Likelihood ratio analysis, as done by the XENON100 collaboration, but do not consider Leff as a nuisance parameter. Instead, Leff is obtained directly from the fits to the data. This enables us to define frequentist confidence intervals by marginalising over Leff.Comment: 10 pages;, 9 figures; references adde

Implication of the PAMELA antiproton data for dark matter indirect detection at LHC

Since the PAMELA results on the "anomalously" high positron fraction and the lack of antiproton excess in our Galaxy, there has been a tremendous number of studies advocating new types of dark matter, with larger couplings to electrons than to quarks. This raises the question of the production of dark matter particles (and heavy associated coloured states) at LHC. Here, we explore a very simple benchmark dark matter model and show that, in spite of the agreement between the PAMELA antiproton measurements and the expected astrophysical secondary background, there is room for large couplings of a WIMP candidate to heavy quarks. Contrary to what could have been naively anticipated, the PAMELA pbar/p measurements do not challenge dark matter model building, as far as the quark sector is concerned. A quarkophillic species is therefore not forbidden.Owing to these large couplings, one would expect that a new production channel opens up at the LHC, through quark--quark and quark--gluon interactions. Alas, when the PDF of the quark is taken into account, prospects for a copious production fade away.Comment: 7 pages, 2 figures, captions of some figures modified, main conclusion unchange

Discovery of a new extragalactic population of energetic particles

We report the discovery of a statistically significant hardening in the Fermi-LAT $\gamma$-ray spectrum of Centaurus A's core, with the spectral index hardening from $\Gamma_{1}=2.73 \pm 0.02$ to $\Gamma_{1}=2.29 \pm 0.07$ at a break energy of ($2.6 \pm 0.3$) GeV. Using a likelihood analysis, we find no evidence for flux variability in Cen A's core lightcurve above or below the spectral break when considering the entire 8 year period. Interestingly, however, the first $\sim3.5$ years of the low energy lightcurve shows evidence of flux variability at the $\sim3.5 \sigma$ confidence level. To understand the origin of this spectral break, we assume that the low energy component below the break feature originates from leptons in Centaurus A's radio jet and we investigate the possibility that the high energy component above the spectral break is due to an additional source of very high energy particles near the core of Cen A. We show for the first time that the observed $\gamma$-ray spectrum of an Active Galactic Nucleus is compatible with either a very large localized enhancement (referred to as a spike) in the dark matter halo profile or a population of millisecond pulsars. Our work constitutes the first robust indication that new $\gamma$-ray production mechanisms can explain the emission from active galaxies and could provide tantalizing first evidence for the clustering of heavy dark matter particles around black holes.Comment: 8 pages, 10 figures. Final version selected as an editor's suggestion and published in Phys. Rev. D. Updated version includes an additional reference that was missing from the final published versio

Reply to 'Comment on ‘Understanding the γ-ray emission from the globular cluster 47 Tuc : evidence for dark matter?'.

Analyzing nine years of Fermi-LAT observations, we recently studied the spectral properties of the prominent globular cluster [Phys. Rev. 98, 041301 (2018)]. In particular, we investigated several models to explain the observed gamma-ray emission, ranging from millisecond pulsars (MSPs) to dark matter (DM), with the motivation for the latter model driven by recent evidence that 47 Tuc harbors an intermediate-mass black hole [B. Kiziltan et al., Nature (London) 542, 203 (2017)]. This investigation found evidence that the observed gamma-ray emission from 47 Tuc is due to two source populations of MSPs and DM. In preceding Comment [Phys. Rev. D 100, 068301 (2019)], Bartels and Edwards comment that this evidence is an artifact of the MSP spectra used in our paper. Here, we reply to this comment and argue that (i) Bartels and Edwards 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

A full reconstruction of two galaxy clusters intra-cluster medium with strong gravitational lensing

Whilst X-rays and Sunyaev–Zel’dovich observations allow to study the properties of the intra-cluster medium (ICM) of galaxy clusters, their gravitational potential may be constrained using strong gravitational lensing. Although being physically related, these two components are often described with different physical models. Here, we present a unified technique to derive the ICM properties from strong lensing for clusters in hydrostatic equilibrium. In order to derive this model, we present a new universal and self-similar polytropic temperature profile, which we fit using the X-COP sample of clusters. We subsequently derive an analytical model for the electron density, which we apply to strong lensing clusters MACS J0242.5-2132 and MACS J0949.8+1708. We confront the inferred ICM reconstructions to XMM-Newton and ACT observations. We contrast our analytical electron density reconstructions with the best canonical β-model. The ICM reconstructions obtained prove to be compatible with observations. However they appear to be very sensitive to various dark matter halo parameters constrained through strong lensing (such as the core radius), and to the halo scale radius (fixed in the lensing optimizations). With respect to the important baryonic effects, we make the sensitivity on the scale radius of the reconstruction an asset, and use the inferred potential to constrain the dark matter density profile using ICM observations. The technique here developed should allow to take a new, and more holistic path to constrain the content of galaxy clusters