In an environment with high-density neutrinos formed in a core-collapse supernova (CCSN), the neutrinos exhibit nonlinear and complex oscillation behaviors due to their self-interactions. The onset of this nonlinear oscillation can be investigated by linearizing the evolution equation for small perturbations around the flavor eigenstates. While the condition under which the flavor eigenstates are unstable has been investigated in many studies, how the perturbations evolve in spacetime has yet to be elucidated. In this paper, we analytically and correctly derive the asymptotic behaviors of the linear perturbations in four-dimensional spacetime in the linear regime for a two-beam neutrino model using the recently proposed Lefschetz thimble formulation. The result suggests that the perturbations grow in the directions between the two neutrino beams. We also briefly discuss the possible effects of neutrino flavor conversion on the explosion mechanism of a CCSN. In particular, the result implies that the flavor instability in the preshock region may propagate into the postshock region, contrary to the previous study focusing on the group velocity in one-dimensional space. How to treat the case of a more realistic continuous spectrum is also discussed.

Neutrinos drive core-collapse supernovae, launch outflows from neutron star merger accretion disks, and set the ratio of protons to neutrons in ejecta from both systems that generate heavy elements in the Universe. Neutrinos of different flavors interact with matter differently, and much recent work has suggested that fast flavor instabilities are likely ubiquitous in both systems, but the final flavor content after the instability saturates has not been well understood. In this work we present particle-in-cell calculations which follow the evolution of all flavors of neutrinos and antineutrinos through saturation and kinematic decoherence. We conduct one-dimensional three-flavor simulations of neutrino quantum kinetics to demonstrate the outcome of this instability in a few example cases. We demonstrate the growth of both axially symmetric and asymmetric modes whose wavelength and growth rate match predictions from linear stability analysis. Finally, we vary the number density, flux magnitude, and flux direction of the neutrinos and antineutrinos and demonstrate that these factors modify both the growth rate and postsaturation neutrino flavor abundances. Weak electron lepton number crossings in these simulations produce both slow growth of the instability and little difference between the flavor abundances in the initial and final states. In all of these calculations the same number of neutrinos and antineutrinos change flavor, making the least abundant between them the limiting factor for postsaturation flavor change. Many more simulations and multidimensional simulations are needed to fully probe the parameter space of the initial conditions.

Working with scalar field theories, we discuss choices of regulator that, inserted in the functional renormalization group equation, reproduce the results of dimensional regularization at one and two loops. The resulting flow equations can be seen as nonperturbative extensions of the $\overline{\mathrm{MS}}$ scheme. We support this claim by recovering all the multicritical models in two dimensions. We discuss a possible generalization to any dimension. Finally, we show that the method also preserves nonlinearly realized symmetries, which is a definite advantage with respect to other regulators.

It has been shown that scalar fields can form gravitationally bound compact objects called boson stars. In this study, we analyze boson star configurations where the scalar fields contain a small amount of angular momentum and find two new classes of solutions. In the first case all particles are in the same slowly rotating state, and in the second case the majority of particles are in the nonrotating ground state and a small number of particles are in an excited rotating state. In both cases, we solve the underlying Gross-Pitaevskii-Poisson equations that describe the profile of these compact objects both numerically as well as analytically through series expansions.

The decays $B_c^{+}\to B_a\overline{\ell }{\nu }_{\ell }$ and $B_c^{+}\to B_a^{*}(\to B_a\gamma )\overline{\ell }{\nu }_{\ell }$, with $a=s$, $d$ and $\ell =e$, $\mu$, are studied in the Standard Model (SM) and in the extension based on the low-energy Hamiltonian comprising the full set of dimension-6 semileptonic $c\to s,d$ operators with left-handed neutrinos. Tests of $\mu /e$ universality are investigated using such modes. The heavy quark spin symmetry is applied to relate the relevant hadronic matrix elements and to exploit lattice QCD results on $B_c$ form factors. Optimized observables are selected, and the pattern of their correlations is studied to identify the effects of the various operators in the extended low-energy Hamiltonian.

Fifth forces arising from hidden sector scalar operator exchange, as probed in a variety of present and planned experiments, can be captured by a general dispersion relation involving one real, positive, spectral density function. Previously considered scalar fifth forces, from tree-level to more exotic loop-level possibilities, are derived in this formalism, without explicitly performing conventional loop calculations. A variety of experimental observables commonly used in fifth force searches are also presented in the same formalism, allowing the straightforward extraction of limits on any specific model. The speculative possibility of probing hidden sector violations of unitarity, causality, or locality, manifested as a breakdown of the positivity of the spectral density, is also discussed.

We propose and experimentally demonstrate a method for detection of a light scalar dark matter (DM) field through probing temporal oscillations of fundamental constants in an atomic optical transition. Utilizing the quantum information notion of dynamic decoupling (DD) in a tabletop setting, we are able to obtain model-independent bounds on variations of $\alpha$ and $m_e$ at frequencies up to the MHz scale. We interpret our results to constrain the parameter space of light scalar DM field models. We consider the generic case, where the couplings of the DM field to the photon and the electron are independent, as well as the case of a relaxion DM model, including the scenario of a DM boson star centered around Earth. Given the particular nature of DD, allowing one to directly observe the oscillatory behavior of coherent DM and considering future experimental improvements, we conclude that our proposed method could be complimentary to, and possibly competitive with, gravitational probes of light scalar DM.

We present lattice Monte Carlo evidence of stable excitations of isolated static charges in the Higgs phase of the charge $q=2$ Abelian Higgs model. These localized excitations are excited states of the interacting fields surrounding the static charges. Since the $q=2$ Abelian Higgs model is a relativistic version of the Landau-Ginzburg effective action of a superconductor, we conjecture that excited states of this kind might be relevant in a condensed matter context. Taken together with recent related work in SU(3) gauge Higgs theory, our result suggests that a massive fermion excitation spectrum may be a general feature of gauge Higgs theories.

We develop a flow-based sampling algorithm for $\mathrm{SU}(N)$ lattice gauge theories that is gauge invariant by construction. Our key contribution is constructing a class of flows on an $\mathrm{SU}(N)$ variable [or on a $\mathrm{U}(N)$ variable by a simple alternative] that respects matrix conjugation symmetry. We apply this technique to sample distributions of single $\mathrm{SU}(N)$ variables and to construct flow-based samplers for SU(2) and SU(3) lattice gauge theory in two dimensions.

Lepton flavor universality can be tested through the ratio of semileptonic $B$ meson decays and leptonic $\mathrm{\Upsilon }$ meson decays, with $\mathrm{\Upsilon }\equiv \mathrm{\Upsilon }(nS)$ ($n=1$, 2, 3). For the charged-current transitions $b\to c\tau {\overline{\nu }}_{\tau }$, discrepancies between the experiment and the Standard Model (SM) have been observed in recent years by different flavor facilities such as BABAR, Belle, and LHCb. While for the neutral-current transitions $b\overline{b}\to \tau \overline{\tau }$, the BABAR experiment reported recently a new measurement of leptonic decay ratio $R_{\mathrm{\Upsilon }(3S)}=\mathrm{BR}(\mathrm{\Upsilon }(3S)\to {\tau }^{+}{\tau }^{-})/\mathrm{BR}(\mathrm{\Upsilon }(3S)\to {\mu }^{+}{\mu }^{-})$, showing an agreement with the SM at the $1.8\sigma$ level. In light of this new BABAR result and regarding the connection between new physics (NP) interpretations to the charged-current $b\to c\tau {\overline{\nu }}_{\tau }$ anomalies and neutral-current $b\overline{b}\to \tau \overline{\tau }$ processes, in this study, we revisit the NP consequences of this measurement within a simplified model with extra massive gauge bosons that coupled predominantly to left-handed leptons of the third generation. We show that the BABAR measurement of $R_{\mathrm{\Upsilon }(3S)}$ cannot easily be accommodated (within its experimental $1\sigma$ range) together with the other $b\to c\tau {\overline{\nu }}_{\tau }$ data, hinting toward a new anomalous observable.

Using $(1310.6\pm 7.0)\times {10}^6$ $J/\psi$ events acquired with the BESIII detector at the BEPCII storage rings, the decay ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-}$ is observed for the first time with a significance of $8\sigma$ via the process $J/\psi \to \gamma {\eta }^{\prime }$. We measure the branching fraction of ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-}$ to be $\mathcal{B}({\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-})=(1.97\pm 0.33(\mathrm{stat})\pm 0.19(\mathrm{syst}))\times {10}^{-5}$, where the first and second uncertainties are statistical and systematic, respectively.

In this work we study the problem of linear stability of gravitational perturbations in stationary and spherically symmetric wormholes. For this purpose, we employ the Newman-Penrose formalism which is well suited for treating gravitational radiation in general relativity, as well as the geometrical aspect of this theory. With this method we obtain a “master equation” that describes the behavior of gravitational perturbations that are of odd parity in the Regge-Wheeler gauge. This equation is later applied to a specific class of Morris-Thorne wormholes and also to the metric of an asymptotically flat scalar field wormhole. The analysis of the equations that these space-times yield reveals that there are no unstable vibrational modes generated by the type of perturbations here studied.

We discuss the weight of vacuum energy in various contexts. First, we compute the vacuum energy for flat spacetimes of the form ${\mathbb{T}}^3\times \mathbb{R}$, where ${\mathbb{T}}^3$ stands for a general 3-torus. We discover a quite simple relationship between energy at radius $R$ and energy at radius $\frac{l_s^2}{R}$. Then we consider quantum gravity effects in the vacuum energy of a scalar field in ${\mathbb{M}}_3\times S^1$ where ${\mathbb{M}}_3$ is a general curved spacetime, and the circle $S^1$ refers to a spacelike coordinate. We compute it for general relativity and generic transverse diffeomorphisms theories. In the particular case of unimodular gravity vacuum energy does not gravitate.

We investigate the massless scalar field perturbations of a new loop quantum gravity motivated regular black hole proposed by Ashtekar et al. in [Quantum Transfiguration of Kruskal Black Holes, Phys. Rev. Lett. 121, 241301 (2018), Quantum extension of the kruskal space-time, Phys. Rev. D 98, 126003 (2018)]. The spacetime of this black hole is distinguished by its asymptotic properties: in Schwarzschild coordinates one of the metric functions diverges as $r\to \infty$ even though the spacetime is asymptotically flat. We show that despite this unusual asymptotic behavior, the quasinormal mode potential is well defined everywhere when Schwarzschild coordinates are used. We propose a useful approximate form of the metric, which allows us to produce quasinormal mode frequencies and ringdown waveforms to high accuracy with manageable computation times. Our results indicate that this black hole model is stable against massless scalar field perturbations. We show that, compared to the Schwarzschild black hole, this black hole oscillates with higher frequency and less damping. We also observe a qualitative difference in the power-law tail of the ringdown waveform between this black hole model and the Schwarzschild black hole. This suggests the quantum corrections affect the behavior of the waves at large distances from the black hole.

We investigate the possibility of testing short-distance modifications to general relativity via higher-curvature terms in the fundamental gravity Lagrangian by analyzing their impact on observations of spinning astronomical binary systems. By using effective field theory methods applied to the two-body problem, generic lower bounds on the short-distance scale accompanying high-curvature terms can be set. In particular, we extend known results by deriving spin-dependent effects in binding energy, radiation emission process, and spin precession equations in binary systems, which are the fundamental ingredients to observe spin-dependent effects in gravitational wave detections from compact binary coalescences and spin precession in double binary pulsars.

Gravitational wave bursts with memory (BWMs) can generate measurable, long-lived frequency shifts and permanent angular deflections in distant sources of light. These perturbations vary across the sky with a characteristic spatial pattern and evolve slowly over long periods of time. In this work, we develop formalism that can be used to describe how a BWM influences the spatial pattern of temperature fluctuations in the cosmic microwave background (CMB). We limit our attention to planar gravitational wave fronts—this assumption dramatically simplifies the necessary calculations. Using toy models of the CMB’s primary temperature variation pattern, we demonstrate that a BWM can mix power from a spherical harmonic mode of a certain degree into modes of various other degrees with vastly different $l$ values. In other words, BWM-induced perturbations to the CMB at any angular scale depend in detail on the unperturbed character of the CMB on all angular scales. The tools developed herein will greatly facilitate future analyses of BWM-induced temperature perturbations that incorporate all of the important physics underlying the CMB.

The action of loop quantum gravity includes the Holst term and/or the Nieh–Yan term in addition to the Ricci scalar. These terms are expected to couple nonminimally to the Higgs. Thus the Holst and Nieh–Yan terms contribute to the classical equations of motion, and they can have a significant impact on inflation. We derive inflationary predictions in the parameter space of the nonminimal couplings, including nonminimally coupled terms up to dimension 4. Successful inflation is possible even with zero or negative coupling of the Ricci scalar. Notably, inflation supported by the nonminimally coupled Holst term alone gives almost the same observables as the original metric formulation plateau Higgs inflation. A nonminimally coupled Nieh–Yan term alone cannot give successful inflation. When all three terms are considered, the predictions for the spectral index and tensor-to-scalar ratio span almost the whole range probed by upcoming experiments. This is not true for the running of the spectral index, and many cases are highly tuned.

At sufficiently high densities and low temperatures matter is expected to behave as a degenerate Fermi gas of quarks forming Cooper pairs, namely a color superconductor, as was originally suggested by Alford, Rajagopal, and Wilczek [Nucl. Phys. B537, 443 (1999). The ground state is a superfluid, an electromagnetic insulator that breaks chiral symmetry, called the color-flavor locked phase. If such a phase occurs in the cores of compact stars, the maximum mass may exceed that of hadronic matter. The gravitational-wave signal GW190814 involves a compact object with mass $2.6{\mathrm{M}}_{\odot }$, within the so-called low mass gap. Since it is too heavy to be a neutron star and too light to be a black hole, its nature has not been identified with certainty yet. Here, we show not only that a color-flavor locked quark star with this mass is viable, but also we calculate the range of the model parameters, namely the superconducting gap $\mathrm{\Delta }$ and the bag constant $B$, that satisfies the strict LIGO constraints on the equation of state. We find that a color-flavor locked quark star with mass $2.6{\mathrm{M}}_{\odot }$ satisfies the observational constraints on the equation of state if $\mathrm{\Delta }\ge 200\mathrm{MeV}$ and $B\ge 83\mathrm{MeV}/{\mathrm{fm}}^3$ for a strange quark mass $m_s=95\mathrm{MeV}/c^2$, and attains a radius $(12.7–13.6)\mathrm{km}$ and central density $(7.5–9.8){10}^{14}\mathrm{g}/{\mathrm{cm}}^3$.

IceCube has observed a flux of cosmic neutrinos, with a “bump” in the energy range $10\lesssim E/\mathrm{TeV}\lesssim 100$ that creates a $3\sigma$ tension with $\gamma$-ray data from the Fermi satellite. This has been interpreted as evidence for a population of hidden cosmic-ray accelerators. We propose an alternative explanation of this conundrum on the basis of cold dark matter which decays into sterile neutrinos after oscillations produce the bump in the cosmic neutrino spectrum.

We investigate a non-Abelian vector dark matter candidate $W^{\prime }$ with a MeV–GeV low mass range, accompanied by a dark photon $A^{\prime }$ and a dark $Z^{\prime }$ in the context of a gauged two-Higgs-doublet model. The model is scrutinized by considering various experimental constraints including dark photon searches, electroweak precision data, the relic density of dark matter together with its direct and indirect searches, monojet and Higgs data from the LHC. The viable parameter space indicates that while a dark $Z^{\prime }$ can be the dominant contribution in the relic density due to resonant annihilation of the dark matter, a dark photon is crucial to dark matter direct detection. The model can be further probed in the near future by sub-GeV dark matter and dark photon experiments.