We explore the possibility of redshift-dependent deviations in the contribution of relativistic degrees of freedom to the radiation budget of the cosmos, conventionally parametrized by the effective number of neutrinos $N_{\mathrm{eff}}$, from the predictions of the standard model. We expand the deviations $\mathrm{\Delta }{N}_{\mathrm{eff}}(z)$ in terms of top-hat functions and treat their amplitudes as the free parameters of the theory to be measured alongside the standard cosmological parameters by the Planck measurements of the cosmic microwave background (CMB) anisotropies and baryonic acoustic oscillations, as well as performing forecasts for futuristic CMB surveys such as PICO and CMB-S4. We reconstruct the history of $\mathrm{\Delta }{N}_{\mathrm{eff}}$ and find that with the current data the history is consistent with the standard scenario. Inclusion of the new degrees of freedom in the analysis increases $H_0$ to $68.71\pm 0.44$, slightly reducing the Hubble tension. With the smaller forecasted errors on the $\mathrm{\Delta }{N}_{\mathrm{eff}}(z)$ parametrization modes from future CMB surveys, very accurate bounds are expected within the possible range of dark radiation models.

Gravitational waves (GWs) generated by a first-order phase transition at the electroweak scale are detectable by future space-based detectors like LISA. The lifetime of the resulting shock waves plays an important role in determining the intensity of the generated GWs. We have simulated decaying primordial acoustic turbulence in three dimensions and make a prediction for the universal shape of the energy spectrum by using its self-similar decay properties and the shape of individual shock waves. The shape for the spectrum is used to determine the time dependence of the fluid kinetic energy and the energy containing length scale at late times. The inertial range power law is found to be close to the classically predicted $k^{-2}$ and approaches it with increasing Reynolds number. The resulting model for the velocity spectrum and its decay in time is combined with the sound shell model assumptions about the correlations of the velocity field to compute the GW power spectrum for flows that decay in less than the Hubble time. The decay is found to bring about a convergence in the spectral amplitude and the peak power law that leads to a power law shallower than the $k^9$ of the stationary case.

The location of the baryon acoustic oscillation (BAO) feature in the two-point correlation function (2PCF) of matter produces a standard ruler that is useful for the measurement of the expansion history of the Universe. Inspired by the possibility of reconstructing the positions of protohalos in the initial density field with a novel method rooted in optimal transport theory, we revisit the BAO signal in the protohalo correlation function. Our work examines the performance of a template 2PCF built on a tracer bias relation that includes scale dependence—a term that can be motivated by peaks theory or a general bias expansion. Working in protohalos, halos, and the linear combination of the protohalo and matter fields that is motivated by the continuity equation, we demonstrate that this model accurately captures the shape of the BAO feature and improves the precision of the BAO scale measurement relative to a model that does not include scale-dependent bias by 47% in protohalos, 15% in halos, and 14% in the linear combination of the protohalo and matter fields. Allowing for scale dependence does not appear to introduce any shift in the BAO feature. The precision of the BAO distance scale estimate is highest with the linear combination of the protohalo and matter fields, which offers a factor of 3.5 improvement over Eulerian-space measurements and a factor of 4–8 improvement over the estimate made with protohalos alone.

We propose a novel leptogenesis scenario in the gauged $U(1{)}_{L_{\mu }-L_{\tau }}$ model. Achieving successful leptogenesis in the $U(1{)}_{L_{\mu }-L_{\tau }}$ symmetric phase is challenging due to the absence of a $CP$ phase, caused by restriction from the gauge symmetry. To overcome this issue, we introduce an additional global symmetry, $U(1{)}_{B-L}$, and a scalar field $\mathrm{\Phi }$ responsible for breaking this symmetry. Through the kinetic misalignment mechanism, the Majoron field associated with $U(1{)}_{B-L}$ symmetry breaking has a kinetic motion in the early Universe. Subsequently, time-dependent Majoron field background induces the background $CP$ phase dynamically, leading to successful leptogenesis in the $U(1{)}_{L_{\mu }-L_{\tau }}$ symmetric phase. Furthermore, Majoron itself serves as a dark matter candidate in this scenario. As one of the phenomenological applications, we consider the model that can also explain the muon $g-2$ anomaly.

The goal of this study is to conduct a timely analysis of the high-redshift star-forming galaxy populations, which will be informative in designing next-generation experiments and their extragalactic targets. We use the hydrodynamical simulation MillenniumTNG to model Lyman-alpha emitting galaxies (LAEs) to extract key properties such as their clustering and occupation statistics. We define LAEs through an empirical relation between star formation rate (SFR) and Lyman-alpha flux. We also explore two other definitions, finding that imposing an additional cut on the maximum stellar mass of the galaxy sample, which approximates the effect of a low escape fraction at high halo mass, leads to a 5–10% decrease of the linear bias of the population. As expected, we find that the halo occupation distribution (HOD) mass parameters rapidly decrease with increasing number density. Additionally, the HOD parameter $\sigma$ also decreases with number density, implying that the SFR-halo mass relationship becomes tighter for low-luminosity objects. Surprisingly, the nonlinear clustering, estimated by the parameter $r_0$, is fixed at fixed number density, whereas the linear bias parameter varies with redshift as $b(z)\propto (1+z)$, suggesting that our LAE samples are relatively stable and long-lived. Finally, we study the amount of galaxy assembly bias present at $z=2$, 3 and find that while at $z=2$ it is roughly $\lesssim 10\%$, at $z=3$ it decreases significantly to $\lesssim 5\%$, showing that assembly bias effects become less important at high $z$. While our study is based on a single full-physics simulation, we expect our results to reflect the properties of LAEs in the Universe. We demonstrate that our findings are in good agreement with previous results using both observations and simulations.

Nuclear theory and experiments, alongside astrophysical observations, constrain the equation of state (EOS) of supranuclear-dense matter. Conversely, knowledge of the EOS allows an improved interpretation of nuclear or astrophysical data. In this article, we use several established constraints on the EOS and the new NICER measurement of PSR J0437-4715 to comment on the nature of the primary companion in GW230529 and the companion of PSR J0514-4002E. We find that, with a probability of $\gtrsim 84\%$ and $\gtrsim 68\%$, respectively, both objects are black holes. These likelihoods increase to above 95% when one uses GW170817’s remnant as an upper limit on the TOV mass. We also demonstrate that the current knowledge of the EOS substantially disfavors high masses and radii for PSR $\mathrm{J}0030+0451$, inferred recently when combining NICER with XMM-Newton background data and using particular hot-spot models. Finally, we also use our obtained EOS knowledge to comment on measurements of the nuclear symmetry energy, finding that the large value predicted by the PREX-II measurement displays some mild tension with other constraints on the EOS.

Rigid (uniform) rotation is usually assumed when investigating the properties of mature neutron stars (NSs). Although it simplifies their description, it is an assumption because we cannot observe the NS’s innermost parts. Here, we analyze the structure of NSs in the simple case of “almost rigidity,” where the innermost and outermost parts rotate with different angular velocities. This is motivated by the possibility of NSs having superfluid interiors, phase transitions, and angular momentum transfer during accretion processes. We show that, in general relativity, the relative difference in angular velocity between different parts of an NS induces a change in the moment of inertia compared to that of rigid rotation. The relative change depends nonlinearly on where the angular velocity jump occurs inside the NS. For the same observed angular velocity in both configurations, if the jump location is close to the star’s surface—which is possible in central compact objects (CCOs) and accreting stars—the relative change in the moment of inertia is close to that of the angular velocity (which is expected due to total angular momentum aspects). If the jump occurs deep within the NS, for instance, due to phase transitions or superfluidity, smaller relative changes in the moment of inertia are observed; we found that if it is at a radial distance smaller than approximately 40% of the star’s radius, the relative changes are negligible. Additionally, we outline the relevance of systematic uncertainties that nonrigidity could have on some NS observables, such as radius, ellipticity, and the rotational energy budget of pulsars, which could explain the x-ray luminosity of some sources. Finally, we also show that nonrigidity weakens the universal $I$-Love-$Q$ relations.

We studied the possible presence of dark matter (DM) in neutron stars (NSs) and the structural properties of the DM admixed NSs (DMANSs) in one of our recent works [1]. The feeble interaction between the fermionic DM ($\chi$) with the hadronic matter is introduced through a dark scalar ($\varphi$) and a dark vector ($\xi$) boson as mediators. The allowed range of the mass of the fermionic DM ($m_{\chi }$), for a particular range of DM Fermi momentum ($k_F^{\chi }$), was obtained in the same work [1] with respect to the various astrophysical constraints on the structural properties of compact stars viz., the mass, radius, and tidal deformability. The present work is dedicated to the calculation and study of nonradial oscillation of the DMANSs using Cowling approximation. We particularly investigate the effect of the presence of DM on the fundamental ($f$) mode oscillation frequencies of the DMANSs utilizing the previously obtained range of $m_{\chi }$ for four different hadronic models. In this work we thoroughly investigate how the individual and combined effects of $m_{\chi }$ and $k_F^{\chi }$ affect the $f$-mode oscillation frequency. Within the framework of our DMANS models, for a particular value of $k_F^{\chi }$, the range of $f_{\max }^{\mathrm{DMANS}}$, with respect to the allowed range of $m_{\chi }$, is also obtained in the present work for four different hadronic models. Since in the present era, the 1.4 and $2.01M_{\odot }$ NSs are of special interest after the detection of GW170817 and PSR $\mathrm{J}0740+6620$, we particularly investigate, for the four hadronic models, the range of $f_{1.4}^{\mathrm{DMANS}}$ and $f_{2.01}^{\mathrm{DMANS}}$ with respect to the acceptable range of $m_{\chi }$ corresponding to the range of $k_F^{\chi }$.

We semianalytically investigate the postmerger evolution of the binary quark star merger. The effective-one-body method is employed to estimate the energy and angular momentum dissipation due to gravitational waves in the inspiral phase. Three major mechanisms of energy and angular momentum dissipation are considered in the postmerger phase: mass outflows, neutrinos, and gravitational waves. The proportion of each mechanism could be determined by baryon number, energy and angular momentum conservation laws, as well as the equilibrium model for rotating quark stars. Applying this analysis to the GW170817 event suggests two important conclusions: (1) A remnant quark star whose mass is smaller than the maximum mass of a uniformly rotating quark star can collapse before its rotational energy is dissipated via electromagnetic radiation (i.e., $\sim 100\mathrm{s}$), as the angular momentum left in the remnant quark star might not be large enough to sustain the additional self-gravity of the supramassive quark star due to the angular momentum dissipation of mass outflows, neutrinos, and gravitational waves, and (2) considering a general quark star equation-of-state model, a constraint on the maximum mass of cold and nonrotating quark stars is found as $M_{\mathrm{TOV}}\lesssim 2.35_{-0.17}^{+0.07}{M}_{\odot }$, assuming a delayed collapse occurred before a large fraction of the total rotational energy ($\gtrsim {10}^{53}\mathrm{erg}$) of the merger remnant was deposited into the merger environment for the GW170817 event. These constraints could be improved with future merger events, once there is more evidence of its postmerger evolution channel or information on the amount of postmerger gravitational wave and neutrino emissions inferred from the multimessenger observations.

Capture and annihilation of weakly interacting massive particle (WIMP)-like dark matter in red giant stars can lead to faster-than-expected ignition of the helium core, and thus a lower tip of the red giant branch (TRGB) luminosity. We use Gaia data to place constraints on the dark matter-nucleon cross section using 22 globular clusters with measured TRGB luminosities, and place projections on the sensitivity resulting from 161 clusters with full phase space distributions observed by Gaia. Although limits remain weaker than those from Earth-based direct detection experiments, they represent a constraint that is fully independent of dark matter properties in the solar neighborhood, probing its properties across the entire Milky Way galaxy. Based on our findings, it is likely that the use of the TRGB as a standard candle in $H_0$ measurements is very robust against the effects of dark matter.

The observation of gravitational waves from binary neutron star mergers offers insights into properties of extreme nuclear matter. However, their high-frequency signals in the kHz range are often masked by quantum noise of the laser light used. Here, we propose the “quantum expander with coherent feedback,” a new detector design that features an additional optical cavity in the detector output and an internal squeeze operation. This approach allows us to boost the sensitivity at high frequencies while at the same time providing a compact and tunable design for signal extraction. It also allows us to tailor the sensitivity of the detector to the specific signal frequency range. We demonstrate that our design can improve the sensitivity of the high-frequency detector concept NEMO, increasing the detection rates by around 14%. Our approach promises a new level of flexibility in designing the detectors aimed at high-frequency signals.

A relativistic model of geometrically thin and optically thick accretion disks is worked out for a class of magnetically charged black holes, which are solutions to the Einstein-Maxwell-dilaton theory with a dilaton-coupled Euler-Heisenberg correction. Constraints on black hole parameters are derived from the subextremality condition and energy conditions. The Keplerian orbits, the time-averaged energy flux, the local temperature, the specific luminosity, and the conversion efficiency of accreting mass into radiation are obtained and compared with Schwarzschild and Gibbons-Maeda-Garfinkle-Horowitz-Strominger black holes.

We search for narrow-line optical emission from dark matter decay by stacking dark-sky spectra from the Dark Energy Spectroscopic Instrument (DESI) at the redshift of nearby galaxies from DESI’s Bright Galaxy and Luminous Red Galaxy samples. Our search uses regions separated by 5 to 20 arcsec from the centers of the galaxies, corresponding to an impact parameter of approximately 50 kpc. No unidentified spectral line shows up in the search, and we place a line flux limit of ${10}^{-19}\mathrm{ergs}/\mathrm{s}/{\mathrm{cm}}^2/{\mathrm{arcsec}}^2$ on emissions in the wavelength range of $2000–9000\stackrel{\circ }{\mathrm{A}}$. This places the tightest constraints yet on the two-photon decay of dark matter in the mass range of 5 to 12 eV, with a particle lifetime exceeding $3\times {10}^{25}\mathrm{s}$. This detection limit also implies that the line surface brightness contributed from all dark matter along the line of sight is at least 2 orders of magnitude lower than the measured extragalactic background light (EBL), ruling out the possibility that narrow optical-line emission from dark matter decay is a major source of the EBL.

In this article, we explore a feedback-control protocol in different quantum field theories (QFTs) to study the quantum correlation in nonunitary evolution of quantum systems. Traditional studies on QFTs focus on quantum entanglement of pure states under the unitary evolution, however, we examine quantum correlation in mixed states using quantum energy teleportation (QET), which is an energy transfer protocol by utilizing ground state entanglement, and introduce quantum discord as a measure. QET involves a midcircuit measurement, which disrupts pure state entanglement. Despite this, our analysis demonstrates that quantum discord maintains the correlation throughout the QET process. We conducted numerical analyses with benchmark models including the Nambu-Jona-Lasinio (NJL) model, revealing that quantum discord consistently acts as an order parameter for phase transitions. The model is extended in a way that it has both the chiral chemical potential and the chemical potential, which are useful to study the phase structures mimicking the chiral imbalance between left- and right- quarks coupled to the chirality density operator. In all cases we studied, the quantum discord behaved as an order parameter of the phase transition.

The production of three Higgs bosons could be a stretch goal for the LHC and a strategic case for future colliders. In this work, we analyse the phenomenological prospects of (neutral) triple Higgs compared to di-Higgs boson production, for a range of Higgs-sector extensions from a strong first-order electroweak phase transition perspective. In parallel, we include constraints from existing exotics and Higgs boson measurements that further limit the parameter space of such models. Resonance contributions offer large modifications in particular for triple Higgs production, albeit starting from a small SM expectation. With enhancements of order 40 over the SM, however, experimental efforts to obtain limits at the HL-LHC are well motivated and well placed. This is further highlighted by the potential of these processes to inform the investigation of the thermal history of our Universe.

The discovery of neutrino oscillations implies that neutrinos are massive and mixed, necessitating an extension of the Standard Model, which may require the introduction of nonstandard neutrino interactions (NSIs). We investigate the potential of a high-energy muon collider to probe such NSIs with muons, specifically focusing on muonic forces. By analyzing the monophoton signal from the process ${\mu }^{+}{\mu }^{-}\to \nu \overline{\nu }\gamma$, we explore four-fermion contact interactions involving two muons and two neutrinos. Moreover, we examine minimal models that generate scalar and vector-mediated NSIs and study their phenomenology. Projected sensitivities for the strength of NSIs, ${\epsilon }_{\alpha \beta }^{\mu \mu }$, are presented at a 95% confidence level for a center-of-mass energy of 3 TeV and integrated luminosities of $\mathcal{L}=1$ and $10{\mathrm{ab}}^{-1}$, showcasing the complementarity between a muon collider and other experimental probes.

Axion-like particles (ALPs) are good candidates for mediators to the dark sector. We explore scenarios in which an ALP mediates interactions between dark matter and electroweak gauge bosons. These models yield testable electromagnetic signals in astrophysical, cosmological, and terrestrial probes. We find promising prospects for both indirect detection and accelerator tests, with interesting parameter space already constrained by current experiments. Our work provides concrete benchmarks for future tests of the electroweak ALP portal.

We suggest a simplified model that simultaneously addresses the dark matter problem and gives rise to top-quark flavor changing neutral current (FCNC) interactions at the one-loop order. The model consists of two extra $SU(2{)}_L$ gauge singlets: a colored mediator of spin zero ($S$) and a right-handed fermion ($\chi$); both are odd under an ad hoc $Z_2$ symmetry. The right-handed fermion plays the role of the dark matter candidate. In this model, the presence of the two dark sector particles generates one-loop induced FCNC decays of the top quark into light quarks and bosons such as the gluon, the photon, the $Z$ boson, or the Higgs boson. As a case study, we analyze the top-quark FCNC decays into light quarks ($u$ or $c$) and $Z$ or Higgs bosons. We then study the reliable solutions to the dark matter problem by estimating the regions in the parameter space that are consistent with the Planck measurement of the dark matter relic density. We also revisit the bounds from the searches of dark matter in events with at least one high-$p_T$ jet and large missing transverse energy at the Large Hadron Collider (LHC). We then define four benchmark points that are consistent with the existing constraints from collider experiments and cosmology. We finally estimate, for these benchmark scenarios, the rates of a broad range of channels that can be used to probe the connection between the top FCNC transitions and dark matter, both at the HL-LHC and at a future 100 TeV collider.

The main limitation for preinflationary breaking of Peccei-Quinn (PQ) symmetry is the upper bound on the Hubble rate during inflation from axion isocurvature fluctuations. This leads to a tension between high scale inflation and QCD axions with grand unified theory scale decay constants, which reduces the potential for a detection of tensor modes at next generation cosmic microwave background (CMB) experiments. We propose a mechanism that explicitly breaks PQ symmetry via nonminimal coupling to gravity, that lifts the axion mass above the Hubble scale during inflation and has negligible impact on today’s axion potential. The initially heavy axion gets trapped at an intermediate minimum during inflation given by the phase of the nonminimal coupling, before it moves to its true $CP$-conserving minimum after inflation. During this stage, it undergoes coherent oscillations around an adiabatically decreasing minimum, which slightly dilutes the axion energy density, while still being able to explain the observed dark matter relic abundance. This scenario can be tested by the combination of next generation CMB surveys like CMB-S4 and LiteBIRD with haloscopes such as ABRACADABRA, DMRadio, or CASPEr-Electric.

We study the conditions under which the $CP$ violation in the quark mixing matrix can leak into the scalar potential of the real two-Higgs-doublet model (2HDM) via divergent radiative corrections, thereby spoiling the renormalizability of the model. We show that any contributing diagram must involve 12 Yukawa-coupling insertions and a factor of the $U(1{)}_{\mathrm{PQ}}$-breaking scalar potential parameter ${\lambda }_5$, thereby requiring at least six loops; this also implies that the 2HDM with only softly broken $U(1{)}_{\mathrm{PQ}}$ is safe from divergent leaks of $CP$ violation to all orders. We demonstrate that additional symmetries of the six-loop diagrams in the type I and II 2HDMs guarantee that all of the divergent $CP$-violating contributions cancel at this order. We also show that these symmetries are violated at seven loops and enumerate the classes of diagrams that can contribute to $CP$-violating divergences, providing evidence that the real 2HDM is theoretically inconsistent starting at the seven-loop level.