We constrain six possible extensions to the $\mathrm{\Lambda }$ cold dark matter (CDM) model using measurements from the Dark Energy Survey’s first three years of observations, alone and in combination with external cosmological probes. The DES data are the two-point correlation functions of weak gravitational lensing, galaxy clustering, and their cross-correlation. We use simulated data vectors and blind analyses of real data to validate the robustness of our results to astrophysical and modeling systematic errors. In many cases, constraining power is limited by the absence of theoretical predictions beyond the linear regime that are reliable at our required precision. The $\mathrm{\Lambda }\mathrm{CDM}$ extensions are dark energy with a time-dependent equation of state, nonzero spatial curvature, additional relativistic degrees of freedom, sterile neutrinos with eV-scale mass, modifications of gravitational physics, and a binned ${\sigma }_8(z)$ model which serves as a phenomenological probe of structure growth. For the time-varying dark energy equation of state evaluated at the pivot redshift we find $(w_{\mathrm{p}},w_a)=(-0.99_{-0.17}^{+0.28},-0.9\pm 1.2)$ at 68% confidence with $z_{\mathrm{p}}=0.24$ from the DES measurements alone, and $(w_{\mathrm{p}},w_a)=(-1.03_{-0.03}^{+0.04},-0.4_{-0.3}^{+0.4})$ with $z_{\mathrm{p}}=0.21$ for the combination of all data considered. Curvature constraints of ${\mathrm{\Omega }}_k=0.0009\pm 0.0017$ and effective relativistic species $N_{\mathrm{eff}}=3.10_{-0.16}^{+0.15}$ are dominated by external data, though adding DES information to external low-redshift probes tightens the ${\mathrm{\Omega }}_k$ constraints that can be made without cosmic microwave background observables by 20%. For massive sterile neutrinos, DES combined with external data improves the upper bound on the mass $m_{\mathrm{eff}}$ by a factor of 3 compared to previous analyses, giving 95% limits of $(\mathrm{\Delta }{N}_{\mathrm{eff}},m_{\mathrm{eff}})\le (0.28,0.20\mathrm{eV})$ when using priors matching a comparable Planck analysis. For modified gravity, we constrain changes to the lensing and Poisson equations controlled by functions $\mathrm{\Sigma }(k,z)={\mathrm{\Sigma }}_0{\mathrm{\Omega }}_{\mathrm{\Lambda }}(z)/{\mathrm{\Omega }}_{\mathrm{\Lambda },0}$ and $\mu (k,z)={\mu }_0{\mathrm{\Omega }}_{\mathrm{\Lambda }}(z)/{\mathrm{\Omega }}_{\mathrm{\Lambda },0}$, respectively, to ${\mathrm{\Sigma }}_0=0.6_{-0.5}^{+0.4}$ from DES alone and $({\mathrm{\Sigma }}_0,{\mu }_0)=(0.04\pm 0.05,0.08_{-0.19}^{+0.21})$ for the combination of all data, both at 68% confidence. Overall, we find no significant evidence for physics beyond $\mathrm{\Lambda }\mathrm{CDM}$.

We review the features of Dark Matter as a particle, presenting some old and new instructive models, and looking for their physical implications in the early universe and in the process of structure formation. We also present a schematic of Dark Matter searches and introduce the most promising candidates to the role of Dark Matter particle.

We propose an effective model to describe the bias induced on cosmological observables by Laniakea, the gravitational supercluster hosting the Milky Way, which was defined using peculiar velocity data from Cosmicflows-4 (CF4). The structure is well described by an ellipsoidal shape exhibiting triaxial expansion, reasonably approximated by a constant expansion rate along the principal axes. Our best fits suggest that the ellipsoid, after subtracting the background expansion, contracts along the two smaller axes and expands along the longest one, predicting an average expansion of ∼ -1.1 km/s/Mpc. The different expansion rates within the region, relative to the mean cosmological expansion, induce line-of-sight-dependent corrections in the computation of luminosity distances. We apply these corrections to two low-redshift datasets: the Pantheon+ catalog of type Ia Supernovae (SN Ia), and 63 measurements of Surface Brightness Fluctuations (SBF) of early-type massive galaxies from the MASSIVE survey. We find corrections on the distances of order ∼ 2-3%, resulting in a shift in the inferred best-fit values of the Hubble constant H ₀ of order ΔH ₀ ^SN Ia ≈ 0.5 km/s/Mpc and ΔH ₀ ^SBF ≈ 1.1 km/s/Mpc, seemingly worsening the Hubble tension.

We devise and demonstrate a method to search for nongravitational couplings of ultralight dark matter to standard model particles using space-time separated atomic clocks and cavity-stabilized lasers. By making use of space-time separated sensors, which probe different values of an oscillating dark matter field, we can search for couplings that cancel in typical local experiments. This provides sensitivity to both the temporal and spatial fluctuations of the field. We demonstrate this method using existing data from a frequency comparison of lasers stabilized to two optical cavities connected via a 2220 km fiber link [Schioppo , ], and from the atomic clocks on board the global positioning system satellites. Our analysis results in constraints on the coupling of scalar dark matter to electrons, d m e , for masses between 10 − 19 and 2 × 10 − 15 eV / c 2 . These are the first constraints on d m e alone in this mass range.

The apparent angular size of the shadow of a black hole in an expanding Universe is redshift-dependent. Since cosmological redshifts change with time - known as the redshift drift - all redshift-dependent quantities acquire a time dependence, and _a fortiori_ so do black hole shadows. We find a mathematical description of the black hole shadow drift and show that the amplitude of this effect is of order $10^{-16}$ per day for M87$^{\star}$. While this effect is small, we argue that its non-detection can be used to constrain the accretion rate around supermassive black holes, as well as a novel probe of the equivalence principle. If general relativity is assumed, we infer from the data obtained by the Event Horizon Telescope for M87$^{\star}$ a maximum accretion rate of $|\dot{M}/{M}| \leq 10^5 M_{\odot}$ per year. On the other hand, in the case of an effective gravitation coupling, we derive a constraint of $|\dot{G}/G| \leq 10^{-3}-10^{-4}$ per year. The effect of redshift drift on the visibility amplitude and frequency of the universal interferometric signatures of photon rings is also discussed, which we show to be very similar to the shadow drift. This is of particular interest for future experiments involving spectroscopic and interferometric techniques, which could make observations of photon rings and their frequency drifts viable.