When properly engineered, simple quantum systems such as harmonic oscillators or spins can be excellent detectors of feeble forces and fields. Following a general introduction to this fast growing area of research I will focus on using optomechanical systems as sensors of weak strain fields. We show that certain mechanical systems can compete with interferometric detectors and potentially surpass the gravitational strain limits set by them for pulsar sources within a few months of integration time.

The observed dark matter (DM) abundance in the Universe can be fully accounted for by a minimally coupled spectator scalar field that was light during inflation. In this scenario, dark matter was produced during inflation by amplification of quantum fluctuations of the spectator field. I will discuss the DM isocurvature perturbations that are unavoidably generated in such scenarios and the circumstances under which they are not problematic for the viability of non-thermal DM models.

Despite countless evidence for its existence, the nature of dark matter remains one of the main open questions in modern physics. If the dark matter is composed of heavy particles, dark matter decay or self-annihilation can be expected to produce high energy neutrinos. A dark matter neutrino signature could be detectable by a neutrino telescope, such as The IceCube Neutrino Observatory, a cubic kilometre detector located at the geographic South Pole. With over 5000 optical sensors, IceCube detects the Cherenkov light emitted by particles produced in neutrino interactions in the Antarctic ice.

We present a set of minimal Dirac neutrino mass models and discuss their cosmological consequences. Specifically, such models generate a neutrino mass at tree level and can have a multiple gravitational wave signature through primordial phase transition(s), can explain the asymmetry between matter and antimatter via neutrinogenesis and accommodate a dark matter candidate in dark glueballs or dark baryons. We discuss situations where the effects on the parameter space from different cosmological considerations overlap and are complimentary to collider probes.

I am going to present the search of light dark matter (DM) particles with Charge Coupled Devices (CCDs). A CCD has exquisite energy and spatial resolutions, low-energy threshold and unique background characterization and rejection. The DArk Matter In Ccds (DAMIC) experiment, currently running at the SNOLAB underground laboratory, clearly demonstrates these abilities. I will discuss recent results on the DM scattering on silicon nuclei and electrons, and absorption of hidden photons.

Blazars such as TXS0506+056 are collimated relativistic outflows from active galactic nuclei and among the brightest persistent radiation sources in the universe. The recent detection with the IceCube Observatory of a very-high-energy neutrino from TXS0506+056 in coincidence with a multi-wavelength flare supports the hypothesis that blazars accelerate cosmic rays beyond PeV energies, challenging conventional theoretical models.

I will discuss the various ways that high energy astrophysics can be used to probe the physics at 10^-43 seconds after the big bang.

The problem of moduli stabilisation and inflation are discussed in type IIB/F-theory. Considering a configuration of three intersecting D7 branes with fluxes, it is shown that higher loop effects induce logarithmic corrections to the K\"ahler potential which can stabilise the K\"ahler moduli. When a new Fayet-Iliopoulos term is included, it is also possible to generate the required number of e-foldings and satisfy the conditions for slow-roll inflation.

I explore the cosmological signatures associated with the twin baryons, electrons, photons and neutrinos in the Mirror Twin Higgs framework. I consider a scenario in which the twin baryons constitute a subcomponent of dark matter, and the contribution of the twin photon and neutrinos to dark radiation is suppressed due to late time asymmetric reheating, but remains large enough to be detected in future cosmic microwave background (CMB) experiments.

New frontiers of astroparticle physics have been opened by IceCube's discovery of high-energy cosmic neutrinos. Their origin is a new mystery in the field, and solving this problem may enable us not only to understand the physics of astrophysical sources but also to obtain important clues about the old mystery, the origin of cosmic rays, and to utilize neutrinos as probes of neutrino properties, dark matter, and fundamental physics. In this talk, I discuss implications of the latest results of IceCube observations, with emphases on multi-messenger approaches.