Double gamma-ray lines from unassociated Fermi-LAT sources revisited

We search for the presence of double gamma-ray line from unassociated Fermi-LAT sources including detailed Monte Carlo simulations to study its global statistical significance. Applying the Su & Finkbeiner selection criteria for high-energy photons we obtain a similar excess over the power-law background from 12 unassociated sources. However, the Fermi-LAT energy resolution and the present low statistics does not allow to distinguish a double peak from a single one with any meaningful statistical significance. We study the statistical significance of the fit to data with Monte Carlo simulations and show that the fit agrees almost perfectly with the expectations from random scan over the sky. We conclude that the claimed high-energy gamma-ray excess over the power-law background from unassociated sources is nothing but an artifact of the applied selection criteria and no preference to any excess can be claimed with the present statistics.Comment: 3 pages, 1 figur

Improved bounds on Z3\mathbb{Z}_{3} singlet dark matter

We reconsider complex scalar singlet dark matter stabilised by a $\mathbb{Z}_{3}$ symmetry. We refine the stability bounds on the potential and use constraints from unitarity on scattering at finite energy to place a stronger lower limit on the direct detection cross section. In addition, we improve the treatment of the thermal freeze-out by including the evolution of the dark matter temperature and its feedback onto relic abundance. In the regions where the freeze-out is dominated by resonant or semi-annihilation, the dark matter decouples kinetically from the plasma very early, around the onset of the chemical decoupling. This results in a modification of the required coupling to the Higgs, which turns out to be at most few per cent in the semi-annihilation region, thus giving credence to the standard approach to the relic density calculation in this regime. In contrast, for dark matter mass just below the Higgs resonance, the modification of the Higgs invisible width and direct and indirect detection signals can be up to a factor $6.7$. The model is then currently allowed at $56.8$ GeV to $58.4$ GeV (depending on the details of early kinetic decoupling) $\lesssim M_{S} \lesssim 62.8$ GeV and at $M_{S} \gtrsim 122$ GeV if the freeze-out is dominated by semi-annihilation. We show that the whole large semi-annihilation region will be probed by the near-future measurements at the XENONnT experiment.Comment: 22 pages, 4 figure

Constraints on primordial black hole dark matter from Galactic center X-ray observations

Surprisingly high masses of the black holes inferred from the LIGO & Virgo gravitational wave measurements have lead to speculations that the observed mergers might be due to ${\cal O}(10) M_\odot$ primordial black holes (PBHs). Furthermore, it has been suggested that the whole amount of dark matter (DM) might be in that exotic form. We investigate constraints on the PBH DM using NuSTAR Galactic center (GC) X-ray data. We used a robust Monte Carlo approach in conjunction with a radiatively inefficient PBH accretion model with commonly accepted model parameters. Compared to previous studies we allowed for multiple forms of DM density profiles. Most importantly, our study includes treatment of the gas turbulence, which significantly modifies the relative velocity between PBHs and gas. We show that inclusion of the effects of gas turbulence and the uncertainties related to the DM density profile reduces significantly the gas accretion onto PBHs compared to the claimed values in previous papers. It is highly improbable to obtain accreting PBHs brighter than the NuSTAR point source limit using observationally determined gas velocities. As such, one can safely conclude that GC X-ray observations cannot rule out ${\cal O}(10) M_\odot$ PBH DM.Comment: 8 pages, 5 figures, A&A accepte

A new mechanism for dark energy: the adaptive screening

We describe how known matter effects within a well-motivated particle physics framework can explain the dark energy component of the Universe. By considering a cold gas of particles which interact via a vector mediator, we show that there exists a regime where the gas reproduces the dynamics of dark energy. In this regime the screening mass of the mediator is proportional to the number density of the gas, hence we refer to this phenomenon as "the adaptive screening mechanism". As an example, we argue that such screening mass can result from strong localization of the vector mediators. The proposed dark energy mechanism could be experimentally verified through cosmological observations by the Euclid experiment, as well as by studying properties of dark photons and sterile neutrinos.Comment: Accepted for publication in JHEP. 8 pages, 2 figure

Muon Anomalous Magnetic Moment and Lepton Flavor Violating Tau Decay in Unparticle Physics

We study effects of unparticle physics on muon g-2 and LFV tau decay processes. LFV interactions between the Standard Model sector and unparticles can explain the difference of experimental value of muon g-2 from the Standard Model prediction. While the same couplings generate LFV tau decay, we found that LFV coupling can be of O(0.1 ... 1) without conflict with experimental bounds of LFV tau decay if the scaling dimension of unparticle operator d_{U} > 1.6.Comment: 12 pages, 7 figure

Running of Low-Energy Neutrino Masses, Mixing Angles and CP Violation

We calculate the running of low-energy neutrino parameters from the bottom up, parameterizing the unknown seesaw parameters in terms of the dominance matrix $R$. We find significant running only if the $R$ matrix is non-trivial and the light-neutrino masses are moderately degenerate. If the light-neutrino masses are very hierarchical, the quark-lepton complementarity relation $\theta_c + \theta_{12} = \pi/4$ is quite stable, but $\theta_{13,23}$ may run beyond their likely future experimental errors. The running of the oscillation phase $\delta$ is enhanced by the smallness of $\theta_{13}$, and jumps in the mixing angles occur in cases where the light-neutrino mass eigenstates cross.Comment: 14 pages, 7 figure