If we imagine rewinding the universe to early times, the scale factor shrinks and the existence of a finite spatial volume may play a role in quantum tunneling effects in a closed universe. It has recently been shown that such finite volume effects dynamically generate an effective equation of state that could support a cosmological bounce. In this work we extend the analysis to the case in which a (homogeneous) anisotropy is present, and identify a criteria for a successful bounce in terms of the size of the closed universe and the properties of the quantum field.

We couple the issue of evolution in the laws of physics with that of violations of energy conservation. Avoiding a time dependence in terms of coordinate time, we define evolution as a function of time variables canonically dual to “constants” (such as $\mathrm{\Lambda }$, the Planck mass, or the gravitational coupling), mimicking a procedure associated with one formulation of unimodular gravity. We then introduce variability via a dependence of other fundamental “constants” on these clocks. Although this is not needed, sharper results are obtained if this procedure violates local Lorentz invariance, which we define in the spirit of Horava-Lifshitz theories (modifying a $3+1$ split action, so that a Lorentz invariant 4D reassembly is no longer possible). We find that variability in the “laws of physics” generically leads to violations of energy conservation if either a matter parameter varies as a function of a gravitational clock, or a gravity parameter depends on a matter clock, with the other combinations sterile. In general the matter components associated with the varying parameter or the clock absorb or give off the violated energy. We illustrate this with a variety of clocks (ticking unimodular time, Ricci time, etc.) and parameters (mainly the gravitational and matter speed of light, but also $\mathrm{\Lambda }$). We can accommodate in this construction (and improve on) several early varying speed of light models, allowing for variability effects related to the spatial curvature and $\mathrm{\Lambda }$ to cause creation of radiation and a hot big bang.

The prevailing assumption is that all exoplanets are made of ordinary matter. However, we propose an unconventional possibility that some exoplanets could be made of dark matter, which we name “dark exoplanets.” In this paper, we explore methods to search for dark exoplanets, including the mass-radius relation, spectroscopy, missing transit, and transit light curve. Specifically, we focus on the transit light-curve method and demonstrate how to distinguish partially transparent dark exoplanets from fully opaque ordinary exoplanets using both observed exoplanet data and dark exoplanet mock data. Our analysis shows that dark exoplanets with a large radius (above around 10% of the star radius) and a small optical depth (below around one) can be identified with current telescope sensitivities.

An ultralight axion like particle (ALP) can mediate a macroscopic force with long-range monopole-dipole interactions between the Earth and the Sun, if the Earth is treated as a polarized source. Because of the geomagnetic field, there exists an estimated ${10}^{42}$ polarized electrons within the Earth. These electrons, in a polarized state, can interact with the unpolarized nucleons in the Sun, giving rise to a monopole-dipole potential between the Sun-Earth system. This phenomenon ultimately influences the trajectories of light and celestial bodies, resulting in observable effects such as gravitational light bending, Shapiro time delay, and perihelion precession of planets. We investigate two scenarios for constraining the monopole-dipole coupling strength. In the first scenario, we establish a constraint on the monopole-dipole strength based on a single astrophysical observation for the first time, treating the Earth as a source of polarized electrons. The perihelion precession of Earth sets an upper limit on the monopole-dipole coupling strength as $g_S{g}_P\lesssim 1.75\times {10}^{-16}$ for the ALP of mass $m_a\lesssim 1.35\times {10}^{-18}\mathrm{eV}$. This bound surpasses the limits obtained from gravitational light bending and Shapiro time delay. In the second scenario, constraints on monopole-monopole coupling strength $g_S(\lesssim 3.51\times {10}^{-25})$ arise from the perihelion precession of the planet Mars, while the limit on dipole-dipole coupling strength $g_P(\lesssim 1.6\times {10}^{-13})$ is taken from the measurement of the tip of the red giant branch in $\omega$ Centauri using Gaia DR2 data. Together, they yield a hybrid constraint on the monopole-dipole coupling strength as $g_S{g}_P\lesssim 5.61\times {10}^{-38}$. Our hybrid bound is 3 orders of magnitude more stringent than the Eöt-Wash experiment and 1 order of magnitude stronger than the current hybrid $(\text{Lab}{)}_{\mathrm{S}}^{\mathrm{N}}\times (\text{Astro}{)}_{\mathrm{P}}^{\mathrm{e}}$ limit.

We present, for the first time, recoil velocity estimates for binary neutron star mergers using data from numerical relativity simulations. We find that binary neutron star merger remnants can have recoil velocity of the order of a few tens of kilometers per second and as high as 150 kilometers per second in our dataset. These recoils are attained due to equivalent contributions from the anisotropic gravitational wave emission as well as the asymmetric ejection of dynamical matter during the merger. We provide fits for net recoil velocity as well as its ejecta component as a function of the amount of ejected matter, which may be useful when constraints on the ejected matter are obtained through electromagnetic observations. We also estimate the mass and spin of the remnants and find them to be in the range $[2.34,3.38]M_{\odot }$ and [0.63, 0.82], respectively, for our dataset.

The relativistic Langevin equation poses a number of technical and conceptual problems related to its derivation and underlying physical assumptions. Recently, a method has been proposed in Petrosyan and Zaccone [J. Phys. A 55, 015001 (2022)] to derive the relativistic Langevin equation from a first-principles particle-bath Lagrangian. As a result of the particle-bath coupling, a new “restoring force” term appeared, which breaks translation symmetry. Here we revisit this problem aiming at deriving a fully translation-invariant relativistic Langevin equation. We successfully do this by adopting the renormalization potential protocol originally suggested by Caldeira and Leggett. The relativistic renormalization potential is derived here and shown to reduce to Caldeira and Leggett’s form in the nonrelativistic limit. The introduction of this renormalization potential successfully removes the restoring force and a fully translation-invariant relativistic Langevin equation is derived for the first time. The physically necessary character of the renormalization potential is discussed in analogy with nonrelativistic systems, where it emerges due to the renormalization of the tagged particle dynamics due to its interaction with the bath oscillators (a phenomenon akin to level repulsion or avoided crossing in condensed matter). We discuss the properties that the corresponding non-Markovian friction kernel has to satisfy, with implications ranging from transport models of the quark-gluon plasma to relativistic viscous hydrodynamic simulations and to electrons in graphene.

The detection of a single Higgs boson at the Large Hadron Collider (LHC) has allowed one to probe some properties of it, including the Yukawa and gauge couplings. However, in order to probe the Higgs potential, one has to rely on new production mechanisms, such as Higgs pair production. In this paper, we show that such a channel is also sensitive to the production and decay of a so-called ‘flavon’ field ($H_F$), a new scalar state that arises in models that attempt to explain the hierarchy of the Standard Model (SM) fermion masses. Our analysis also focuses on the other decay channels involving the flavon particle, specifically the decay of the flavon to a pair of $Z$ bosons ($H_F\to ZZ$) and the concurrent production of a top quark and charm quark via the $\varphi \to tc$ decays ($\varphi =H_F,A_F$), having one or more leptons in the final states. In particular, we show that, with $3000{\mathrm{fb}}^{-1}$ of accumulated data at 14 TeV (the Run 3 stage) of the LHC an heavy flavon $H_F$ with mass $M_{H_F}\simeq 2m_t$ can be explored with $3\sigma –5\sigma$ significance through these channels.

Two classes of far detectors have been proposed or are under operation at the LHC. The first class is a series of neutrino detectors that are sensitive to light active neutrinos via either charged-current or neutral-current interactions; exemplary ideas are $\mathrm{FASER}\nu$, SND@LHC, and FLArE. Another type aims primarily at looking for displaced decays of long-lived particles (LLPs) into charged final-state particles, including ANUBIS and FASER. In this work, we propose searches for probing lepton number violation associated with a Majorana active/sterile neutrino, for the first time with these experiments, which, if discovered, would be a clear signature of new physics beyond the Standard Model. With Monte Carlo simulation, we find that while the neutrino detectors, unfortunately, are estimated to have signal-event rates orders of magnitude below $\mathcal{O}(1)$, some LLP far detectors such as ANUBIS, if upgraded, would be most promising for discovering a Majorana sterile neutrino of mass $\mathcal{O}(1)\mathrm{GeV}$ in certain so-far unexcluded parameter space. In this exploratory work, we emphasize on the importance of leveraging the LHC far detectors for purposes beyond the planned ones, such as searching for lepton number violation.

This work investigates the implications of very special relativity (VSR) on the calculation of vacuum polarization for fermions in the presence of Maxwell and Kalb-Ramond gauge fields in four-dimensional spacetime. We derive the SIM(2)-covariant gauge theory associated with an Abelian antisymmetric two-tensor and its corresponding field strength. We demonstrate that the free VSR-Kalb-Ramond electrodynamics is equivalent to a massive scalar field with a single polarization. Furthermore, we determine an explicit expression for the effective action involving Maxwell and Kalb-Ramond fields due to fermionic vacuum polarization at one-loop order. The quantum corrections generate divergences free of nonlocal terms only in the VSR-Maxwell sector. At the same time, we observe UV/IR mixing divergences due to the entanglement of VSR-nonlocal effects with quantum higher-derivative terms for the Kalb-Ramond field. However, in the lower energy limit, the effective action can be renormalized like in the Lorentz invariant case.

We propose a supersymmetric extension of the minimal $U(1{)}_X$ model, along with a new $Z_2$ parity. One of the salient features of this model relates to how both the $U(1{)}_X$ gauge symmetry and R parity are broken radiatively at the TeV scale by the vacuum expectation value of a $Z_2$-even right-handed sneutrino. By assigning one right-handed neutrino $Z_2$-odd parity, it can remain a viable dark matter (DM) candidate, despite R parity being broken. Furthermore, the DM relic abundance receives an enhanced annihilation cross section due to the $U(1{)}_X$ gauge boson ($Z^{\prime }$) resonance and is in agreement with the current observations. We have also found a complementarity that exists between the observed DM relic abundance and search results for the $Z^{\prime }$ boson resonance at the Large Hadron Collider, which further constrains the parameter space of our $U(1{)}_X$ model. Finally, we consider a $SU(5)\times U(1{)}_x$ grand unified theory extension and investigate the complementarities mentioned previously.

The initiation of a novel neutrino physics program at the Large Hadron Collider (LHC) and the purpose-built Forward Physics Facility (FPF) proposal have motivated studies exploring the discovery potential of these searches. This requires resolving degeneracies between new predictions and uncertainties in modeling neutrino production in the forward kinematic region. The present work investigates a broad selection of existing predictions for the parent hadron spectra at $\mathrm{FASER}\nu$ and the FPF to parametrize expected correlations in the neutrino spectra produced in their decays and to determine the highest achievable precision for their observation based on Fisher information. This allows for setting constraints on various physics processes within and beyond the Standard Model, including neutrino non-standard interactions. We also illustrate how combining multiple neutrino observables could lead to experimental confirmation of the enhanced-strangeness scenario proposed to resolve the cosmic-ray muon puzzle already during the ongoing LHC run 3.

Composite Higgs extensions of the Standard Model provide an explanation for the large hierarchies between the Yukawa couplings. We study their realization in the context of fundamental partial compositeness where the Standard Model fermions mix linearly with bound states of the new sector, consisting of a fermion and a scalar. The properties of this composite are unraveled with the functional renormalization group approach using dynamically emergent composites. Specifically, we extract the scaling of correlation functions along a walking regime and provide indicative estimates for the minimal incarnation of the theory.

We present the numerical equivalence between the Wilson flow and stout-link smearing, both of which are known to be a well-established technique for smoothing the gauge fields on the lattice. Although the conceptional correspondence between two methods was first pointed out by Lüscher in his original paper [J. High Energy Phys. 08 (2010) 071], we provide a direct analytical proof of the equivalence between the two methods at finite lattice spacing $a$ in the zero limit of the stout-smearing parameter $\rho$. The leading order corrections start at $\mathcal{O}(\rho )$, which would induce $\mathcal{O}(a^2)$ corrections. It is, therefore, not obvious that they remain equivalent even with finite parameters ($a\ne 0$ and $\rho \ne 0$) within some numerical precision. In this paper, we demonstrate the equivalence of both methods by directly comparing the expectation value of the action density, which is measured in actual numerical simulations.

In this work, we analyze a large class of effective Yang-Mills-Higgs models constructed in terms of adjoint scalars. In particular, we reproduce asymptotic properties of the confining string, suggested by lattice simulations of $SU(N)$ pure Yang-Mills theory, in models that are stable in the whole range of Higgs-field mass parameters. These properties include $N$-ality, Abelian-like flux-tube profiles, independence of the profiles with the $N$-ality of the quark representation, and Casimir scaling. We find that although these models are formulated in terms of many fields and possible Higgs potentials, a collective behavior can be established in a large region of parameter space, where the desired asymptotic behavior is realized.

We demonstrate some shortcomings of “fixing the equations,” an increasingly popular remedy for time evolution problems of effective field theories (EFTs). We compare the EFTs and their “fixed” versions to the UV theories from which they can be derived in two cases: K-essence and nonlinear Proca theory. We find that when an EFT breaks down due to loss of hyperbolicity, fixing does not approximate the UV theory well if the UV solution does not quickly settle down to vacuum. We argue that this can be related to the EFT approximation itself becoming invalid, which cannot be rectified by fixing.

Light dark matter (DM) in the GeV ballpark faces weaker constraint from direct detection experiments. If such DM also has sufficient self-interactions due to a light mediator, it can alleviate the small-scale problems of the cold dark matter (CDM) paradigm while being consistent with the latter at large scales, as suggested by astrophysical observations. However, generating the correct thermal relic for such light DM is challenging. While GeV scale CDM typically leads to thermal overproduction due to the absence of sufficient annihilation channels, self-interacting dark matter (SIDM) typically has an under-abundant thermal relic due to its large annihilation rates into mediator particles. In this Letter, we propose a minimal realization of GeV scale SIDM with correct thermal relic, where one of the three singlet fermions, responsible for seesaw origin of light neutrino masses, assists in generating correct SIDM relic density via freeze-out. The setup thereby encompasses astrophysical as well as cosmological aspects of light DM while simultaneously providing a solution to the origin of light neutrino mass. Because of such a connection to several frontiers, there exist exciting discovery prospects in terms of direct and indirect search of DM, laboratory and cosmology based dark photon signatures and effective light neutrino mass.

We present an innovative approach to the linearly polarized gluons confined inside the unpolarized nucleon in lepton-nucleon scattering. Our method analyzes the correlation of energy flows at azimuthal separations $\varphi$. The interference of the spinning gluon with both positive and negative helicities translates into a $\cos (2\varphi )$ asymmetry imprinted on the detector. Unlike the conventional transverse momentum dependent probes, the $\cos (2\varphi )$ asymmetry in this approach is preserved by rotational symmetry, holds to all orders, and is free of radiation contamination and is thus expected to provide the exquisite signature of the nucleon linearly polarized gluons.

The electric dipole moment (EDM) of elementary particles, arising from flavor-diagonal $CP$ violation, serves as a powerful probe for new physics beyond the Standard Model and holds the potential to provide novel insights in unraveling the puzzle of the matter-dominated Universe. Hyperon EDM is a largely unexplored territory. In this paper, we present a comprehensive angular analysis that focuses on entangled hyperon-antihyperon pairs in $J/\psi$ decays for the indirect extraction of hyperon EDM. The statistical sensitivities are investigated for BESIII and the proposed Super Tau-Charm Facility (STCF). Leveraging the statistics from the BESIII experiment, the estimated sensitivity for $\mathrm{\Lambda }$ EDM can reach an impressive level of ${10}^{-19}e\mathrm{cm}$, achieving a 3-orders-of-magnitude improvement over the only existing measurement in a fixed-target experiment at Fermilab with similar statistics. The estimated sensitivities for the ${\mathrm{\Sigma }}^{+}$, ${\mathrm{\Xi }}^{-}$, and ${\mathrm{\Xi }}^0$ hyperons at the same level of ${10}^{-19}e\mathrm{cm}$ will mark the first-ever achievement and the latter two will be the first exploration of hyperons with two strange valence quarks. The EDM measurements for hyperons conducted at the BESIII experiment will be a significant milestone and serve as a litmus test for new physics such as supersymmetry and the left-right symmetrical model. Furthermore, at the STCF experiment, the sensitivity of hyperon EDM measurements can be further enhanced by 2 orders of magnitude. Additionally, this angular analysis enables the determination of $CP$ violation in hyperon decays, the effective weak mixing angle, and beam polarization.

Sign and magnitude of the thermodynamic curvature provides empirical information about the nature of microstructures of a general thermodynamic system. For charged black holes in anti–de Sitter (AdS), thermodynamic curvature is positive for large charge or chemical potential, and diverges for extremal black holes, indicating strongly repulsive nature. We compute the thermodynamic curvature at low temperatures, for charged black holes with ${\mathrm{AdS}}_2$ near horizon geometry, and containing a zero temperature horizon radius $r_h$, in a spacetime which asymptotically approaches ${\mathrm{AdS}}_D$ (for $D>3$). In the semiclassical analysis at low temperatures, the curvature shows a novel crossover from negative to positive side, indicating the shift from attraction to repulsion dominated regime near $T=0$, before diverging as $1/(\gamma T)$, where $\gamma$ is the coefficient of leading low temperature correction to entropy. Accounting for quantum fluctuations, the curvature computed in the canonical ensemble is positive, whereas the one in the grand canonical ensemble, shows a crossover from negative to positive side in the Schwarzian region. Moreover, the divergence of curvature at $T=0$ is cured irrespective of the ensemble used, resulting in a universal constant, inversely related to the number of symmetry generators of vacuum ${\mathrm{AdS}}_2$.