Primordial magnetic fields in the dark sector can be transferred to magnetic fields in the visible sector due to a gauge kinetic mixing term. We show that the transfer occurs when the evolution of magnetic fields is dominated by dissipation due to finite electric conductivity, and does not occur at later times if the magnetic fields evolve according to magnetohydrodynamics scaling laws. The efficiency of the transfer is suppressed by not only the gauge kinetic mixing coupling but also the ratio between the large electric conductivity and the typical momentum of the magnetic fields. We find that the transfer gives nonzero visible magnetic fields today. However, without possible dynamo amplifications, the field transfer is not efficient enough to obtain the intergalactic magnetic fields suggested by the gamma-ray observations, although there are plenty of possibilities for efficient dark magnetogenesis, which are experimentally unconstrained.

The recent LIGO-Virgo detection of gravitational waves from a binary neutron star inspiral event GW170817 and the discovery of its accompanying electromagnetic signals mark a new era for multimessenger astronomy. In the coming years, advanced gravitational-wave detectors are likely to detect tens to hundreds of similar events. Neutron stars in binaries can possess significant spin, which is imprinted on the gravitational waveform via the effective spin parameter ${\chi }_{\mathrm{eff}}$. We explore the astrophysical inferences made possible by gravitational-wave measurements of ${\chi }_{\mathrm{eff}}$. First, using a fiducial model informed by radio observations, we estimate that $\approx 15–30\%$ of binary neutron stars should have spins measurable at $\gtrsim 90\%$ confidence level by advanced detectors assuming the spin axis of the recycled neutron star aligns with the total orbital angular momentum of the binary. Second, using Bayesian inference, we show that it is possible to tell whether or not the spin axis of the recycled neutron star tends to be aligned with the binary orbit using $\gtrsim 30$ detections. Finally, interesting constraints can be placed on neutron star magnetic field decay after $\gtrsim 300$ detections, if the spin periods and magnetic field strengths of Galactic binary neutron stars are representative of the merging population.

We thoroughly study the photo-disintegration of ${}^4\mathrm{He}$ on the cosmic microwave background using the most recent cross-section data from both the inclusive measurement observing the analog of the giant dipole resonance in ${}^4\mathrm{He}$ through the charge-exchange spin-flip ${}^4\mathrm{He}$ (${}^7\mathrm{Li},{}^7\mathrm{Be}$) reaction and from measurements of exclusive two-body and three-body processes: ${}^4\mathrm{He}(\gamma ,p){}^3\mathrm{H}$, ${}^4\mathrm{He}(\gamma ,n){}^3\mathrm{He}$, and ${}^4\mathrm{He}(\gamma ,pn){}^2\mathrm{H}$. We show that the present-day (redshift $z=0$) mean-free path of ultrarelativistic (Lorentz factor $\sim {10}^{10}$) helium nuclei increases by more that 15% with respect to previous estimates adopted as benchmarks for Monte Carlo simulation codes of ultrahigh-energy cosmic ray propagation. This implies that the physical survival probability of ${}^4\mathrm{He}$ nuclei would be larger than predicted by existing event generators. For example, for $E\sim 10^{10.8}\mathrm{GeV}$ and a propagation distance of 3.5 Mpc, the ${}^4\mathrm{He}$ intensity would be 35% larger than the output of the CRPropa 3 program and 42% larger than the output of the SimProp v2r4 program. We provide new parametrizations for the two-body and three-body photo-disintegration cross sections of ${}^4\mathrm{He}$, ${}^3\mathrm{He}$, tritium, and deuterium.

We present an updated impact parameter dependent saturation model determined through a fit to the combined HERA I and $\mathrm{I}+\mathrm{II}$ reduced cross section data. The same HERA data are used to fit the linearized version of the applied dipole amplitude, which makes it possible to estimate the magnitude of the saturation effects in various experiments. We find that both parametrizations provide comparable descriptions of the considered data when an effective confinement scale dynamics is incorporated with quark masses. Moreover, it is possible to consistently determine the light and charm quark masses. The role of potentially nonperturbatively large dipoles is examined in detail, with the result that, especially in the case of the structure function $F_2$, their contribution is numerically significant. The potential to discriminate between the two models in future $e+p$ and $e+A$ experiments is also illustrated.

I consider a theory of a real scalar and a fermion field, with a Yukawa interaction and a potential term that admits two degenerate minima at the tree level. The quantum vacuum energy difference between these two vacua can be calculated using the renormalization group improved effective potential, and gives a finite, nonzero result, dependent on the relative strength of the scalar and the Yukawa interactions.

The study of the top quark’s properties is an important part of the LHC program. In earlier work, we have studied the rare decay $t\to b\overline{b}c$, using effective operators to capture the effects of physics beyond the Standard Model. However top decay is primarily sensitive to new physics in the sub-TeV energy regime. If this new physics resides at a higher energy scale, then one needs to turn to single-top production. In this paper, we use the $s$-channel and $t$-channel single-top production measurements to constrain the new physics parameter space associated with such contact interactions. We also study the net top polarization as a means to distinguish between contributions from operators involving different fermion chiralities and Lorentz structures.

We investigate the phenomenology of scalar singlet dark matter candidates that couple dominantly to the Standard Model via a Yukawa interaction with the top quark and a colored vectorlike fermion. We estimate the viability of this vectorlike portal scenario with respect to the most recent bounds from dark matter direct and indirect detection, as well as to dark matter and vectorlike mediator searches at colliders. Moreover, we take QCD radiative corrections into account in all our theoretical calculations. This work complements analyses related both to models featuring a scalar singlet coupled through a vectorlike portal to light quarks and to scenarios in which the dark matter is a Majorana singlet coupled to the Standard Model through scalar colored particles (akin to simplified models inspired by supersymmetry). Our study puts especially forward the complementarity of different search strategies from different contexts, and we show that current experiments allow for testing dark matter masses ranging up to 700 GeV and mediator masses ranging up to 6 TeV.

We analyze the maximum contributions to the muon magnetic moment $a_{\mu }$ and Yukawa and triple Higgs couplings in the flavor-aligned two-Higgs doublet model (2HDM). We focus on the most promising case of a light pseudoscalar Higgs $A$ with large Yukawa couplings to leptons and quarks. Taking into account experimental constraints from LHC Higgs and flavor physics, we find maximum possible Yukawa couplings of a light $A$ of around 50–100 (leptons) and $\mathcal{O}(0.5)$ (quarks). An overall maximum of $a_{\mu }$ of more than $45\times {10}^{-10}$ is possible in a very small parameter region around $M_A=20\mathrm{GeV}$. For $M_A$ up to 100 GeV, the maximum possible value of $a_{\mu }$ is compatible with the currently observed deviation if the $A$ couplings to quarks and leptons are both large, making this scenario promising for LHC searches. We also analyze the subleading bosonic two-loop contributions to $a_{\mu }$, finding values up to $3\times {10}^{-10}$.

We develop an approach to quantum dynamics based on quantum phase space trajectories. The latter are built from a unitary irreducible representation of the symmetry group of the respective classical phase space. We use a quantum action functional to derive the basic equations. In principle, our formulation is equivalent to the Hilbert space formulation. However, the former allows for consistent truncations to reduced phase spaces in which approximate quantum dynamics can be derived. We believe that our approach can be very useful in the domain of quantum cosmology and therefore, we use the cosmological phase space example to establish the basic equations of this formalism.

A new class of modified theory of gravity is introduced where the volume form becomes dynamical. This approach is motivated by unimodular gravity and can also be related to Brans-Dicke theory. On the level of the action, the only change made will be through the volume element which is used in the integration. This is achieved by the introduction of a fourth-order tensor which connects the spacetime metric to the new volume form. Using dynamical systems techniques, this model is studied in the context of cosmology. The most interesting result is that there exist parameter ranges where this model starts undergoing an epoch of accelerated expansion, followed by a decelerating expansion which evolves to a final epoch of accelerated expansion.

We perform fully nonlinear numerical simulations to study aspherical deformations of the critical self-similar solution in the gravitational collapse of ultrarelativistic fluids. Adopting a perturbative calculation, Gundlach predicted that these perturbations behave like damped or growing oscillations, with the frequency and damping (or growth) rates depending on the equation of state. We consider a number of different equations of state and degrees of asphericity and find very good agreement with the findings of Gundlach for polar $\ell =2$ modes. For sufficiently soft equations of state, the modes are damped, meaning that, in the limit of perfect fine-tuning, the spherically symmetric critical solution is recovered. We find that the degree of asphericity has at most a small effect on the frequency and damping parameter or on the critical exponents in the power-law scalings. Our findings also confirm, for the first time, Gundlach’s prediction that the $\ell =2$ modes become unstable for sufficiently stiff equations of state. In this regime, the spherically symmetric self-similar solution can no longer be recovered by fine-tuning to the black-hole threshold, and one can no longer expect power-law scaling to hold to arbitrarily small scales.

The quasinormal modes associated with gravitational-wave signals from binary black hole (BBH) mergers can provide deep insight into the remnant’s properties. Once design sensitivity is achieved, present ground-based gravitational-wave interferometers could detect potentially hundreds of BBH signals in the coming years. But for most, the ringdown phase will have a very weak signal-to-noise ratio (SNR), and therefore poor, if any, scientific information could be extracted from them. We review how a summation method can help detect these weak (2,2) QNMs and potentially allow us to use their information. The method is based on two main steps: the signal’s rescaling and synchronization. In this first study, we tested the method under limited BBH parameters and review its principal limitations. In particular, the synchronization that fails for the weakest signals requires selecting ringdowns with a SNR above 2.6. Using this threshold, we show that for two different BBH populations 40% to 70% of all the potential detections could still be used for the summation while ensuring a summed SNR of $\sim 80\%$ of the maximal achievable SNR (i.e., for ideally synchronized signals).

The equations of state for a characteristic spacetime are studied in the context of the spherically symmetric interior exact and analytical solutions in Hořava gravity and Einstein-æther theory in which anisotropic fluids are considered. In particular, for a given anisotropic interior solution, the equations of state relating the density to the radial and tangential pressure are derived, by means of a polynomial best fit. Moreover, the well-known relativistic polytropic equations of state are used in order to obtain the profile of the thermodynamical quantities inside the stellar object as provided by the specific exact solution considered. It is then shown that these equations of state need to be modified in order to account for the profiles of density and pressures.

The reconstruction of an inflationary universe in the context of the Galileon model or $G$-model, considering as attractors the scalar spectral index $n_S(N)$ and the tensor to scalar ratio $r(N)$ as a function of the number of e-folding $N$ is studied. By assuming a coupling of the form $G(\varphi ,X)=g(\varphi )X$, we obtain the effective potential $V$ and the coupling parameter $g$ in terms of the cosmological parameters $n_S$ and $r$ under the slow roll approximation. From some examples for $n_S(N)$ and $r(N)$, different results for the effective potential $V(\varphi )$ and the coupling parameter $g(\varphi )$ are found.

We introduce a new family of primordial cosmological perturbations that are not described by traditional power spectra. At the linear level, these perturbations live in the kernel of the spatial Laplacian operator, and thus we call them cosmological zero modes. We compute the cosmic microwave background temperature and polarization anisotropy induced by these modes and forecast their detection sensitivity using a cosmic-variance limited experiment. In particular, we consider two configurations for the zero modes: The first configuration consists of stochastic metric perturbations described by white noise on a “holographic screen” located at our cosmological horizon. The amplitude of the power spectrum of this white noise can be constrained to be $\lesssim 9\times {10}^{-14}$. The second configuration is a primordial monopole beyond our cosmological horizon. We show that such a monopole, with “charge” $Q$, can be detected in the cosmic microwave background sky up to a distance of $11.6Q^{1/4}\times \text{horizon}$ radius (or $160Q^{1/4}\mathrm{Gpc}$). More generally, observational probes of cosmological zero modes can shed light on nonperturbative phenomena in the primordial Universe, beyond our observable horizon.

It is well known that gravitons can convert into photons, and vice versa, in the presence of cosmological magnetic fields. We study this conversion process in the context of the atomic dark matter scenario. In this scenario, we can expect cosmological dark magnetic fields, which are free from the stringent constraint from the cosmic microwave observations. We find that gravitons can effectively convert into dark photons in the presence of cosmological dark magnetic fields. The graviton-dark photon conversion effect may open up a new window for ultrahigh frequency gravitational waves.

We adopt the fluid conduction approximation to study the evolution of spherical star clusters and self-interacting dark matter (SIDM) halos. We also explore the formation and dynamical impact of density cusps that arise in both systems due to the presence of a massive, central black hole. The large N-body, self-gravitating systems we treat are “weakly collisional”: the mean free time between star or SIDM particle collisions is much longer than their characteristic crossing (dynamical) time scale, but shorter than the system lifetime. The fluid conduction model reliably tracks the “gravothermal catastrophe” in star clusters and SIDM halos without black holes. For a star cluster with a massive, central black hole, this approximation reproduces the familiar Bahcall-Wolf quasistatic density cusp for the stars bound to the black hole and shows how the cusp halts the “gravothermal catastrophe” and causes the cluster to re-expand. An SIDM halo with an initial black hole central density spike that matches onto to an exterior NFW profile relaxes to a core-halo structure with a central density cusp determined by the velocity dependence of the SIDM interaction cross section. The success and relative simplicity of the fluid conduction approach in evolving such “weakly collisional,” quasiequilibrium Newtonian systems motivates its extension to relativistic systems. We present a general relativistic extension here.

Earth-based gravitational-wave detectors will be limited by quantum noise in a large part of their spectrum. The most promising technique to achieve a broadband reduction of such noise is the injection of a frequency-dependent squeezed vacuum state from the output port of the detector, with the squeeze angle rotated by the reflection off a Fabry-Perot filter cavity. One of the most important parameters limiting the squeezing performance is represented by the optical losses of the filter cavity. We report here the operation of a 300 m filter cavity prototype installed at the National Astronomical Observatory of Japan. The cavity is designed to obtain a rotation of the squeeze angle below 100 Hz. After achieving the resonance of the cavity with a multiwavelength technique, the round trip losses have been measured to be between 50 and 90 ppm. This result demonstrates that with realistic assumptions on the input squeeze factor and the other optical losses, a quantum noise reduction of at least 4 dB in the frequency region dominated by radiation pressure can be achieved.

We show that the upper bound of the classical QCD axion window can be significantly relaxed for low-scale inflation. If the Gibbons-Hawking temperature during inflation is lower than the QCD scale, the initial QCD axion misalignment angle follows the Bunch-Davies distribution. The distribution is peaked at the strong $CP$ conserving minimum if there is no other light degree of freedom contributing to the strong $CP$ phase. As a result, the axion overproduction problem is significantly relaxed even for an axion decay constant larger than $10^{12}\mathrm{GeV}$. We also provide concrete hilltop inflation models where the Hubble parameter during inflation is comparable to or much smaller than the QCD scale, with successful reheating taking place via perturbative decays or dissipation processes.