Neutron stars are known to show accelerated spin-up of their rotational frequency called a glitch. Highly magnetized rotating neutron stars (pulsars) are frequently observed by radio telescopes (and in other frequencies), where the glitch is observed as irregular arrival times of pulses which are otherwise very regular. A glitch in an isolated neutron star can excite the fundamental ($f$)-mode oscillations which can lead to gravitational wave generation. This gravitational wave signal associated with stellar fluid oscillations has a damping time of 10–200 ms and occurs at the frequency range between 2.2–2.8 kHz for the equation of state and mass range considered in this work, which is within the detectable range of the current generation of ground-based detectors. Electromagnetic observations of pulsars (and hence pulsar glitches) require the pulsar to be oriented so that the jet is pointed toward the detector, but this is not a requirement for gravitational wave emission which is more isotropic and not jetlike. Hence, gravitational wave observations have the potential to uncover nearby neutron stars where the jet is not pointed towards the Earth. In this work, we study the prospects of finding glitching neutron stars using a generic all-sky search for short-duration gravitational wave transients. The analysis covers the high-frequency range from 1–4 kHz of LIGO–Virgo detectors for signals up to a few seconds. We set upper limits for the third observing run of the LIGO–Virgo detectors and present the prospects for upcoming observing runs of LIGO, Virgo, KAGRA, and LIGO India. We find the detectable glitch size will be around ${10}^{-5}\mathrm{Hz}$ for the fifth observing run for pulsars with spin frequencies and distances comparable to the Vela pulsar. We also present the prospects of localizing the direction in the sky of these sources with gravitational waves alone, which can facilitate electromagnetic follow-up. We find that for the five detector configuration, the localization capability for a glitch size of ${10}^{-5}\mathrm{Hz}$ is around $132{\mathrm{deg}}^2$ at $1\sigma$ confidence for 50% of events with distance and spin frequency as that of Vela.

We put constraints on the normalized energy density in gravitational waves from cosmic domain walls by searching for the stochastic gravitational-wave background in the data of Advanced LIGO and Virgo’s first three observing runs. By adopting a phenomenological broken power-law model, we obtain the upper limit on the amplitude of stochastic gravitational-wave background generated by domain walls in the peak frequency band 10–200 Hz and get the most stringent limitation ${\mathrm{\Omega }}_{\mathrm{DW}}(f_{*}=35\mathrm{Hz})<1.4\times {10}^{-8}$ at 95% confidence level at the peak frequency $f_{*}=35\mathrm{Hz}$. Subsequently, we work out the constraints on the parameter space in the appealing realization of DW structure—the heavy axion model which can avoid the so-called quality problem.

Current searches for gravitational waves from compact-binary objects are primarily designed to detect the dominant gravitational-wave mode and assume that the binary components have spins which are aligned with the orbital angular momentum. These choices lead to observational biases in the observed distribution of sources. Sources with significant spin-orbit precession or unequal-mass-ratios, which have non-negligible contributions from subdominant gravitational-wave modes, may be missed; in particular, this may significantly suppress or bias the observed neutron star–black hole (NSBH) population. We simulate a fiducial population of NSBH mergers and determine the impact of using searches that only account for the dominant-mode and aligned spin. We compare the impact for the Advanced LIGO design, $\mathrm{A}+$, LIGO Voyager, and Cosmic Explorer observatories. We find that for a fiducial population where the spin distribution is isotropic in orientation and uniform in magnitude, we will miss $\sim 25\%$ of sources with mass-ratio $q>6$ and up to $\sim 60\%$ of highly precessing sources $({\chi }_p>0.5)$, after accounting for the approximate increase in background. In practice, the true observational bias can be even larger due to strict signal-consistency tests applied in searches. The observation of low spin, unequal-mass-ratio sources by Advanced LIGO design and Advanced Virgo may in part be due to these selection effects. The development of a search sensitive to high mass-ratio, precessing sources may allow the detection of new binaries whose spin properties would provide key insights into the formation and astrophysics of compact objects.

We show that macroscopic dark matter (DM) impacts on the degenerate helium cores of red-giant branch (RGB) stars can ignite helium fusion via DM-baryon elastic scattering. The onset of helium burning leads to a characteristic drop in luminosity and rise in temperature that marks the transition to a horizontal branch star. We show that such impacts can alter the RGB luminosity function of globular clusters (GCs), focusing in particular on the GC M15. Using models of M15 stars constructed with the stellar simulation code MESA, we compute the expected DM-ignition event rates and the theoretical RGB luminosity functions under the null and signal hypotheses. We constrain DM with masses ${10}^{17}\mathrm{g}\lesssim m_{\chi }\lesssim {10}^{20}\mathrm{g}$ and geometric cross sections ${10}^2{\mathrm{cm}}^2\lesssim {\sigma }_{\chi n}\lesssim {10}^7{\mathrm{cm}}^2$ assuming that the DM in M15 is sourced by the background Milky Way halo. We also place more stringent constraints assuming that M15 formed in a DM subhalo that survives today.

Correlated red noise recently reported from pulsar timing observations may be an indication of stochastic gravitational waves emitted by cosmic strings that formed during a primordial phase transition near the grand unification energy scale. Unfortunately, known probes of cosmic strings, namely the cosmic microwave background anisotropies and string lensing of extragalactic galaxies, are not sensitive enough for low dimensionless string tensions of $G\mu c^{-2}={10}^{-10}-{10}^{-7}$ (where the tension $\mu$ is the string energy per unit length) that are needed to explain this putative signal. We show that strong gravitational lensing of fast radio bursts (FRBs) by cosmic strings is a potentially unambiguous avenue to probe that range of string tension values. The image pair of string lensing are expected to have identical magnification factor and parity, and have a typical time delay of $\sim {10}^2(G\mu c^{-2}/{10}^{-8}{)}^2\mathrm{s}$. The unique spectral fingerprint of each FRB, as well as the possibility to detect correlations in the time series of the electric field of the radio waves, will enable verification of the string lensing interpretation. Very-long-baseline interferometry observations can spatially resolve the image pair and provide a lower bound on the string tension based on the image separation. We calculate the FRB lensing rate as a function of the FRB detection number for several different models of the FRB redshift distribution. We find that a survey detecting $\sim {10}^5$ FRBs, in line with estimates for the detection rate of the forthcoming survey CHORD, can uncover a strong lensing event for a string tension of $G\mu c^{-2}\simeq {10}^{-7}$. Larger FRB surveys, such as Phase 2 of the Square Kilometre Array, have the potential to significantly improve the sensitivity on the string tension to $G\mu c^{-2}\simeq {10}^{-9}$.

We study the partial fragmentation of a strange quark star into strangelets during the process of merger of two strange quark stars. We discuss the fate of the fragments considering their possible evaporation into nucleons. We show that only a rather small amount of large size strangelets, ejected from the spiral arms in the postmerger, survives a total evaporation into nucleons. In this way we demonstrate that (1) the density of strangelets in the galaxy is too low to trigger the conversion of all neutron stars into strange quark stars, and it allows the coexistence of both types of compact objects; (2) the probability of direct detection of a strangelet is negligible, and therefore its nondetection is compatible with the strange quark matter hypothesis; (3) most of the matter ejected during and after the merger of two strange quark stars evaporates into nucleons, and therefore it can generate a kilonova-like signal.

We present results of an all-sky search for continuous gravitational waves which can be produced by spinning neutron stars with an asymmetry around their rotation axis, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. Four different analysis methods are used to search in a gravitational-wave frequency band from 10 to 2048 Hz and a first frequency derivative from $-{10}^{-8}$ to ${10}^{-9}\mathrm{Hz}/\mathrm{s}$. No statistically significant periodic gravitational-wave signal is observed by any of the four searches. As a result, upper limits on the gravitational-wave strain amplitude $h_0$ are calculated. The best upper limits are obtained in the frequency range of 100 to 200 Hz and they are $\sim 1.1\times {10}^{-25}$ at 95% confidence level. The minimum upper limit of $1.10\times {10}^{-25}$ is achieved at a frequency 111.5 Hz. We also place constraints on the rates and abundances of nearby planetary- and asteroid-mass primordial black holes that could give rise to continuous gravitational-wave signals.

The connection between the spin distribution and the topological structure of the baryon is an open and important problem. Here we address it using QCD in ($1+1$) spacetime dimensions, which is exactly solvable at large number of colors $N$. It is found that the distribution of chirality inside a baryon is drastically different from a chirality distribution inside states with zero baryon number, “mesons.” This difference is shown to arise from the topological structure of the baryon—at large $N$, all of the baryon’s chirality is concentrated near $x=0$, whereas in a meson state it vanishes in the small $x$ limit. Our results illustrate how the constituent features of the baryon reemerge and are tied to the topological features of the bosonized solitonic solution. Possible implications for QCD in ($3+1$) dimensions and for deep inelastic scattering experiments are discussed.

We develop a complete formulation of quantum gauge invariance in light-front dynamics for interacting theories with massless vector gauge fields in the framework of null-plane causal perturbation theory. We apply the general results to quantum electrodynamics, showing that the so-called “gauge terms” present in the photon commutation distribution when quantized under the null-plane gauge condition have no contribution in the calculation of the physical $S$-operator matrix elements at any order. We use this result to prove the normalizability of the theory, and to calculate the electron’s self-energy at second order.

Inspired by the states $T_{cs0}(2900{)}^0$, $T_{cs1}(2900{)}^0$, $T_{c\overline{s}0}^a(2900{)}^0$, and $T_{c\overline{s}0}^a(2900{)}^{++}$ reported by the LHCb Collaboration, we carry out a systematical investigation on the properties of the ground and $P$-wave states $[cs][\overline{u}\overline{d}]$ and $[cu][\overline{s}\overline{d}]$ with various spin, isospin, or $U$ spin and color combinations in a multiquark color flux-tube model. Matching our results with the spin-parity and mass of the states $T_{cs0}(2900{)}^0$ and $T_{cs1}(2900{)}^0$, we can describe them as the compact states $[cs][\overline{u}\overline{d}]$ with $I(J^P)=1(0^{+})$ and $0(1^{-})$ in the model, respectively. The ground state $T_{cs0}(2900{)}^0$ is mainly made of strongly overlapped axial vector $[cs{]}_{{\overline{\mathbf{3}}}_c}$ and axial vector $[\overline{u}\overline{d}{]}_{{\mathbf{3}}_c}$. The $P$-wave state $T_{cs1}(2900{)}^0$ dominantly consists of a gradually separated scalar or axial vector $[cs{]}_{{\overline{\mathbf{3}}}_c}$ and a scalar $[\overline{u}\overline{d}{]}_{{\mathbf{3}}_c}$ in the shape of a dumbbell. Supposing the states $T_{c\overline{s}0}^a(2900{)}^0$ and $T_{c\overline{s}0}^a(2900{)}^{++}$ belong to the same isospin triplet, the mass of the state ${[[cu{]}_{{\overline{\mathbf{3}}}_c}[\overline{s}\overline{d}{]}_{{\mathbf{3}}_c}]}_{{\mathbf{1}}_c}$ with symmetrical $U$ spin and $J^P=0^{+}$ is highly consistent with that of the states $T_{c\overline{s}0}^a(2900{)}^0$ and $T_{c\overline{s}0}^a(2900{)}^{++}$ in the model. After coupling two color configurations, the state $[cu][\overline{s}\overline{d}]$ is slightly lighter than the states $T_{c\overline{s}0}^a(2900{)}^0$ and $T_{c\overline{s}0}^a(2900{)}^{++}$. In addition, we also discuss the properties of other states in the model.

The chiral soliton lattice (CSL) is a lattice structure composed of domain walls aligned in parallel at equal intervals, which is energetically stable in the presence of a background magnetic field and a finite (baryon) chemical potential due to the topological term originated from the chiral anomaly. We study its formation from the vacuum state, with describing the CSL as a layer of domain-wall disks surrounded by the vortex or string loop, based on the Nambu-Goto-type effective theory. We show that the domain wall nucleates via quantum tunneling when the magnetic field is strong enough. We evaluate its nucleation rate and determine the critical magnetic field strength with which the nucleation rate is no longer exponentially suppressed. We apply this analysis to the neutral pion in the two-flavor QCD as well as the axionlike particles (ALPs) with a finite (baryon) chemical potential under an external magnetic field. In the former case, even though the CSL state is more energetically stable than the vacuum state and the nucleation rate becomes larger for a sufficiently strong magnetic field, it cannot be large enough so that the nucleation of the domain walls is not exponentially suppressed and promoted, without suffering from the tachyonic instability of the charged pion fluctuations. In the latter case, we confirm that the effective interaction of the ALPs generically includes the topological term required for the CSL state to be energetically favored. We show that the ALP CSL formation is promoted if the magnetic field strength and the chemical potential of the system is slightly larger than the scale of the axion decay constant.

The sole static electromagnetic property of a spin-$\frac{1}{2}$ Majorana fermion is its anapole moment. Though they cannot couple to single real photons, these particles can interact with electric currents through virtual photons. If a Majorana fermion is immersed in a background current, there is an energy difference between the spin states of the fermion; the higher energy state has its anapole moment antialigned with the current. In this paper, we address the ability of a system of initially unpolarized Majorana fermions to achieve some degree of polarization relative to a static background current. In considering processes that allow the Majorana fermion’s spin to flip to the lower-energy state, we focus upon two irreversible processes: the spontaneous emission of two real photons and the emission of a single real photon emitted in virtual Compton scattering. Both of these processes involve coupling to photons via the fermion’s polarizabilities. We compute the spin-flip transition rates for these processes using a low-energy expansion of the Hamiltonian and construct a toy model to showcase how these rates depend upon the underlying parameters within a model. Applying these ideas to a thermal dark matter (DM) model, we find that when the DM thermally decouples from the Standard Model plasma in the early universe, two-photon emission is negligible but partial polarization for the DM medium can proceed via virtual Compton scattering if sufficient currents exist.

Hadronization is a complex quantum process whereby quarks and gluons become hadrons. The widely used models of hadronization in event generators are based on physically inspired phenomenological models with many free parameters. We propose an alternative approach whereby neural networks are used instead. Deep generative models are highly flexible, differentiable, and compatible with graphical processing units. We make the first step towards a data-driven machine learning-based hadronization model. In that step, we replace a component of the hadronization model within the Herwig event generator (cluster model) with $\mathsf{HADML}$, a computer code implementing a generative adversarial network. We show that a $\mathsf{HADML}$ is capable of reproducing the kinematic properties of cluster decays. Furthermore, we integrate it into $\mathsf{Herwig}$ to generate entire events that can be compared with the output of the public $\mathsf{Herwig}$ simulator as well as with $e^{+}{e}^{-}$ data.

The $U(1)$ extensions of the Standard Model contain a heavy neutral gauge boson $Z^{\prime }$. If leptophobic, the boson can evade the stringent bounds from the dilepton resonance searches. We consider two theoretically well-motivated examples of leptophobic $U(1)$ extensions in which the $Z^{\prime }$ decays to right-handed neutrinos (RHNs) with substantial branchings. The coexistence of a leptophobic $Z^{\prime }$ and the RHNs opens up a new possibility of searching for these particles simultaneously through the production of a $Z^{\prime }$ at the LHC and its decay to a RHN pair. For this decay to occur, the RHNs need to be lighter than the $Z^{\prime }$. Hence, we study this process in an inverse seesaw setup where the RHNs can be in the TeV range. However, in this case, they have a pseudo-Dirac nature, i.e., a RHN pair would produce only opposite-sign lepton pairs, as opposed to the Majorana-type neutrinos, which can produce both same- and opposite-sign lepton pairs. Hence, the final state we study has a same-flavor opposite-sign lepton pair plus hadronically decaying boosted $W$ bosons. Our analysis shows that the high luminosity LHC can discover a TeV-scale leptophobic $Z^{\prime }$ decaying via a RHN pair in a wide range of available parameters. Interestingly, large parameter regions beyond the reach of future dijet-resonance searches can be probed exclusively through our channel.

Primordial black holes (PBHs) play as a novel source to radiate light elementary particles of energies in the region of a few hundred MeV. We explore the possibility that the light axionlike particles (ALPs) are produced from PBH evaporation. The absorption of light ALPs in the underground detector targets then induces energetic photoelectron signatures in current and future neutrino experiments. Utilizing the PBH ALP event rate, we place general exclusion limits on the axion couplings at Super-K and Hyper-K. We also translate these limits into the upper bound on the fraction of dark matter composed of PBHs $f_{\mathrm{PBH}}$.

The origin of neutrino mass is a big unsolved problem of the Standard Model (SM) that motivate us to consider beyond the SM (BSM) scenarios where SM-singlet right-handed neutrinos (RHNs) are introduced to explain the origin of the light neutrino masses through the seesaw mechanism. There is a variety of ways which could lead us to this goal, and one of them is a general U(1) extension of the SM. In this scenario, three SM-singlet RHNs are introduced to cancel the gauge and mixed gauge gravity anomalies. After anomaly cancellation, we notice that the left- and right-handed charged fermions are differently charged under the general U(1) gauge group evolving a chiral scenario. After the breaking of the general U(1) symmetry, a neutral BSM gauge boson $(Z^{\prime })$ acquires mass, and it is a free parameter. Such $Z^{\prime }$, being lighter than 5 GeV, could be probed at the intensity and lifetime frontiers like FASER, FASER2, DUNE, and ILC beam dump experiments. The estimated bounds are needed to be compared with the existing bounds. We find that existing constraints from Orsay, Nomad, PS191, KEK, LSND, CHARM experiments, and cosmological scenario like SN1987A can be compared in our case once estimated for chiral scenarios. Finally, we compare the parameter spaces showing viable ones that could be probed by FASER, FASER2, DUNE, and ILC beam dump experiments and already excluded regions from Orsay, Nomad, PS191, KEK, LSND, CHARM, and SN1987A for a chiral scenario.

We consider the general class of theories in which there is a new ultralight scalar field that mediates an equivalence principle violating, long-range force. In such a framework, the Sun and Earth act as sources of the scalar field, leading to potentially observable location-dependent effects on atomic and nuclear spectra. We determine the sensitivity of current and next-generation atomic and nuclear clocks to these effects and compare the results against the existing laboratory and astrophysical constraints on equivalence principle violating fifth forces. We show that, in the future, the annual modulation in the frequencies of atomic and nuclear clocks in the laboratory caused by the eccentricity of Earth’s orbit around the Sun may offer the most sensitive probe of this general class of equivalence principle violating theories. Even greater sensitivity can be obtained by placing a precision clock in an eccentric orbit around Earth and searching for time variation in the frequency, as is done in anomalous redshift experiments. In particular, an anomalous redshift experiment based on current clock technology would already have a sensitivity to fifth forces that couple primarily to electrons at about the same level as the existing limits. Our study provides well-defined sensitivity targets to aim for when designing future versions of these experiments.

The search for dark matter (DM) at colliders is founded on the idea of looking for something invisible. There are searches based on production and decay processes where DM may reveal itself as missing energy. If nothing is found, our best tool to constrain the parameter space of many extensions of the Standard Model (SM) with a DM candidate is the Higgs boson. As the measurements of the Higgs couplings become increasingly precise, higher-order corrections will start to play a major role. The tree-level contribution to the invisible decay width provides information about the portal coupling. Higher-order corrections also give us access to other parameters from the dark sector of the Higgs potential that are not present in the tree-level amplitude. In this work we will focus on the complex singlet extension of the SM in the phase with a DM candidate. We calculate the one-loop electroweak corrections to the decay of the Higgs boson into two DM particles. We find that the corrections are stable and of the order of a few percent. The present measurement of the Higgs invisible branching ratio, $\mathrm{BR}(H\to \mathrm{invisible})<0.11$, already constrains the parameter space of the model at leading order. We expect that by the end of the LHC the experimental measurement will require the inclusion of the electroweak corrections to the decay in order to match the experimental accuracy. Furthermore, the only competing process, which is direct detection, is shown to have a cross section below the neutrino floor.

We present the first exploratory lattice quantum chromodynamics (QCD) calculation of the polarized gluon Ioffe-time pseudodistribution in the nucleon. The Ioffe-time pseudodistribution provides a frame-independent and gauge-invariant framework to determine the gluon helicity in the nucleon from first principles. We employ a high-statistics computation using a ${32}^3\times 64$ lattice ensemble characterized by a 358 MeV pion mass and a 0.094 fm lattice spacing. We establish the pseudodistribution approach as a feasible method to address the proton spin puzzle with successive improvements in statistical and systematic uncertainties anticipated in the future. Within the statistical precision of our data, we find a good comparison between the lattice determined polarized gluon Ioffe-time distribution and the corresponding expectations from the state-of-the-art global analyses. We find a hint for a nonzero gluon spin contribution to the proton spin from the model-independent extraction of the gluon helicity pseudodistribution over a range of Ioffe-time, $\nu \lesssim 9$.