In this paper, we explore the impact of field redefinition on the spectrum of linearized perturbations in relativistic hydrodynamics. We observe that the spectrum of hydrodynamics modes is never affected by the local field redefinition, however, the spectrum of the nonhydrodynamic modes is affected. Through an appropriate all-order redefinition, nonhydrodynamic modes can be eliminated, leading to a new frame where the spectrum contains only hydrodynamic modes. We also observe that the resulting stress-energy tensor may have an infinite series in momentum space, with a convergence radius linked to the eliminated nonhydrodynamic mode. In certain special cases, higher-order terms in the stress-energy tensor under field redefinition may cancel, indicating that nonhydrodynamic modes are mere artifacts of the fluid variable choice and hold no physical significance, even if they appear to violate physical constraints. Using a special toy example, we find a criterion to distinguish between physical and unphysical nonhydrodynamic modes.

We revisit, reformulate, and extend a method for determining the neutrino mass ordering by using precision measurements of the atmospheric $\mathrm{\Delta }{m}^2\mathrm{s}$ in both electron and muon neutrino disappearance channels, first proposed by the authors in 2005 [H. Nunokawa et al., Phys. Rev. D 72, 013009 (2005)]. The mass ordering is a very important outstanding question for our understanding of the elusive neutrino and determination of the mass ordering has consequences to particle physics, nuclear physics, and cosmology. The JUNO reactor experiment will start data taking this year, and the precision of the atmospheric $\mathrm{\Delta }{m}^2\mathrm{s}$ from electron antineutrino measurements will improve by a factor of 3 from Daya Bay’s 2.4% to 0.8% within a year. This measurement, when combined with the atmospheric $\mathrm{\Delta }{m}^2$’s measurements from T2K and NOvA for muon neutrino disappearance, will contribute substantially to the $\mathrm{\Delta }{\chi }^2$ between the two remaining neutrino mass orderings. In this paper we derive for the first time a mass ordering sum rule that can be used to address the possibility that JUNO’s atmospheric $\mathrm{\Delta }{m}^2$’s measurement, when combined with other experiments in particular T2K and NOvA, can determine the neutrino mass ordering at the $3\sigma$ confidence level within one year of operation. For a confidence level of $5\sigma$ in a single experiment, we will have to wait until the middle of the next decade when the DUNE experiment is operating.

Utilizing a dataset of $6.7{\mathrm{fb}}^{-1}$ from electron-positron collisions recorded by the BESIII detector at the BEPCII storage ring, a search is conducted for the processes $e^{+}{e}^{-}\to \varphi {\chi }_{c0}$ and $\varphi {\eta }_{c2}(1D)$ across center-of-mass energies from 4.47 to 4.95 GeV. In the absence of any significant signals, upper limits are set. These include limits on the dressed cross sections for $e^{+}{e}^{-}\to \varphi {\chi }_{c0}$, as well as the product of the dressed cross section for $e^{+}{e}^{-}\to \varphi {\eta }_{c2}(1D)$ and a sum of five branching fractions. Furthermore, the product of the electronic width of $Y(4660)$ and the branching fraction of the $Y(4660)\to \varphi {\chi }_{c0}$, denoted as ${\mathrm{\Gamma }}_{e^{+}{e}^{-}}^{Y(4660)}{\mathcal{B}}_{Y(4660)\to \varphi {\chi }_{c0}}$, is determined to be $<0.35\mathrm{eV}$ at the 90% confidence level.

Here we suggest a new local action describing arbitrary integer spin-$s$ massless particles in terms of only two symmetric fields $\phi$ and $\alpha$ of rank-$s$ and ($s-3$) respectively. It is an unconstrained version of the Fronsdal theory where the double traceless constraint on the physical field is evaded via a rank-($s-4$) Weyl like symmetry. The constrained higher spin diffeomorphism is enlarged to full diffeomorphism via the Stueckelberg field $\alpha$ through an appropriate field redefinition. After a partial gauge fixing where the Weyl symmetry is broken while preserving diffeomorphisms, the field equations reproduce, for arbitrary integer spin-$s$, diffeomorphism invariant equations of motion previously obtained via a truncation of the spectrum of the open bosonic string field theory in the tensionless limit. In the $s=4$ case we show that the functional integration over $\alpha$ leads to a unique nonlocal Weyl and diffeomorphism invariant action given only in terms of the physical field $\phi$ whose spectrum is confirmed via an analysis of the analytic structure of the spin-4 propagator for which we introduce a complete basis of projection and transition nonlocal differential operators. We also show that the elimination of $\alpha$ after the Weyl gauge fixing leads to a nonlocal diffeomorphism invariant action previously obtained in the literature.

Recently, several LQCD simulations have proven that the interaction in the isoscalar channel in $D{D}^{*}$ scattering is attractive. This channel is naturally connected to the $T_{cc}(3875{)}^{+}$ which is observed in the $D^0{D}^0{\pi }^{+}$ invariant mass distribution. However, it remains an open question whether the virtual bound state found in these several LQCD simulations is actually linked to the LHCb experimental observation. In this article we perform an EFT-based analysis of the LQCD data and demonstrate that a proper chiral extrapolation leads to a $T_{cc}$ pole compatible with experiment. At the physical pion mass, we find a virtual bound state with a binding energy $\mathrm{\Delta }E=-0.06(\genfrac{}{}{0ex}{}{+1.30}{-2.20})(\genfrac{}{}{0ex}{}{+0.50}{-1.11})$. Moreover, we extract from a global analysis both the light and heavy quark mass dependence of the $T_{cc}$ pole and study the role of the $\rho$- and $\pi$-meson exchanges.

We study the applicability of the finite temperature effective potential in the equation of motion of a homogeneous “misaligned” scalar condensate $\phi$ and find important caveats that severely restrict its domain of validity: (i) the assumption of local thermodynamic equilibrium is in general not warranted, (ii) we show a direct relation between the effective potential and the thermodynamic entropy density $\mathcal{S}=-\partial V_{\mathrm{eff}}(T,\phi )/\partial T$, which entails that for a dynamical $\phi (t)$ the entropy becomes a nonmonotonic function of time, (iii) parametric instabilities in both cases with and without spontaneous symmetry breaking lead to profuse particle production with nonthermal distribution functions, (iv) in the case of spontaneous symmetry breaking spinodal instabilities yield a complex effective potential, internal energy and entropy, an untenable situation in thermodynamics. All these caveats associated with using the effective potential in the equation of motion of the condensate cannot be overcome by finite temperature equilibrium resummation schemes. We argue that the dynamics of the condensate leads to decoupling and freeze-out from local thermodynamic equilibrium, and propose a closed quantum system approach based on unitary time evolution. It yields the correct equations of motion without the caveats of the effective potential, and provides a fully renormalized and thermodynamically consistent framework to study the dynamics of the “misaligned” condensate, with real and conserved energy and entropy amenable to numerical study. The evolution of the condensate leads to profuse stimulated particle production with nonthermal distribution functions. Possible emergent asymptotic nonthermal states and eventual rethermalization are conjectured.

Laser pulse collisions are a promising tool for the investigation of light-by-light scattering phenomena induced by quantum vacuum fluctuations. Using the numerical code based on the vacuum emission picture and put forward in [1], we observe a strong dependence of the signal features on the transverse profiles of the colliding laser pulses in the interaction region. For a probe beam tailored such as to feature an annular far-field profile and a pronounced on-axis focus peak counterpropagating a pump beam at zero impact parameter, the signal’s main emission direction can undergo the analog of a phase transition with the beam-waist ratio of the pulses serving as a control parameter. Depending on the pump’s beam profile, this phase transition can be first order (e.g., for a pump with a flat-top far-field profile) or second order (e.g., for a Gaussian pump). From the simulation data, we determine the critical point and extract the corresponding critical exponent for the second-order transition of the main emission direction of the signal in the far field. For this, we improve the performance of the above numerical code, using the phase transition analogs as an example to illustrate the capabilities and limitations of the code and current workflows.

In this paper, we investigate the Higgs boson decay process $H\to f\overline{f}Z\to f\overline{f}{\mu }^{-}{\mu }^{+}$, where $f$ denotes any light fermions, at the next-to-leading order (NLO) accuracy. The calculation is performed within the framework of single-pole approximation, in which the contributions of different polarization states of the $Z$ boson are considered separately. Numerical results show that, by taking appropriate cut, the nonresonant background is negligible, and the NLO corrections are 1%–4% of the LO contributions. We also find that the inclusion of NLO corrections can greatly reduce the dependence on the electroweak coupling scheme, and enhance the prediction reliability. We formulate a method for the extraction of the pseudo-observable ${\mathrm{\Gamma }}^{H\to ffZ}$ from the $f\overline{f}{\mu }^{-}{\mu }^{+}$ signal.

The stability of the standard model (SM) Higgs vacuum is a long-standing issue in particle physics. The SM Higgs quartic coupling parameter is expected to become negative at high scales, potentially generating an unstable vacuum well before reaching the Planck scale. We investigate whether the introduction of vectorlike leptons (VLLs) in six distinct gauge anomaly-independent representations can stabilize the SM vacuum without introducing additional scalar fields. By analyzing the mass spectrum and mixing angles of these VLLs with the SM leptons, we identify conditions under which the Higgs potential remains stable. We demonstrate that there exists a set of allowed but narrowed VLL spectra that can indeed stabilize the SM vacuum. We also study the effect of these VLLs on electroweak precision observables, particularly the oblique parameters $\mathbb{S}$ and $\mathbb{T}$, to ensure the fit within global experimental constraints. Finally, we perform a comprehensive analysis of the parameter space allowed by electroweak precision data and the parameter space required for stability, highlighting cases that accommodate both. This study opens up new avenues for understanding the role of vectorlike leptons in extending the validity of the standard model up to the Planck scale.

$R$-parity can be extended to a continuous global $\mathrm{U}(1{)}_R$ symmetry. We investigate whether an anomalous $\mathrm{U}(1{)}_R$ can be identified as the Peccei-Quinn symmetry suitable for solving the strong $CP$ problem within supersymmetric extensions of the Standard Model. In this case, $\mathrm{U}(1{)}_R$ is broken at some intermediate scale and the quantum chromodynamics axion is the $R$-axion. Moreover, the $R$-symmetry can potentially be gauged via the Green-Schwarz mechanism within completions to supergravity, in order to evade the axion quality problem. Obstacles to realizing this scenario are highlighted and phenomenologically viable approaches are identified.

The extradimensional axion solves the strong $CP$ problem while largely circumventing the quality problem that plagues its four-dimensional counterparts. Such high quality can be clearly understood in terms of the generalized global symmetries of the higher-dimensional theory. We emphasize that an electric one-form symmetry is entirely responsible for protecting the potential of axions arising from 5D gauge theories and use this to systematically characterize the extradimensional axion quality problem. We identify three ways of breaking this one-form symmetry to generate an axion potential: adding electrically charged matter, gauging a magnetic higher-form symmetry, and turning on an Adler-Bell-Jackiw anomaly. In the latter case, we identify new ways of generating an axion potential via extradimensional magnetic monopoles. We also discuss how the axion is modified if the protective electric one-form symmetry is itself gauged. Finally, we relate these effects to gravitational expectations for the quality problem via generalized weak gravity conjectures. The clarity that generalized symmetries bring to the extradimensional axion quality problem highlights their relevance to particle phenomenology.

The precision measurements of the muon magnetic moment and the $W$ boson mass have sparked interest in the potential deviations from standard model (SM) predictions. While it may be premature to attribute any excesses in these precision measurements to new physics, they do offer a valuable indication of potential directions for physics beyond the SM. Additionally, the particle nature of dark matter (DM) remains a crucial enigma. Despite the absence of any definitive DM signal in direct detection and collider experiments, the Galactic Center GeV $\gamma$-ray excess and the AMS-02 antiproton ($\overline{p}$) excess could potentially offer hints related to the evidence of DM. Motivated by these observations, we propose a simple DM model that addresses all these issues. This model extends the SM by incorporating singlet and doublet Dirac fermion fields, along with a doublet complex scalar field. For the viable parameter regions in this model, we find that future upgrades of the Large Hadron Collider and DM direct detection experiments can only partially probe them, while future high-energy muon colliders hold promise for exploring the unexplored parameter space.

Leptoquarks (LQs) can contribute to the magnetic and electric dipole moments of charged leptons, which the current experiments have measured with good accuracy. We revisit the parameter spaces of TeV-scale vector LQs that contribute to these observables and study how these models fare against the LHC bounds. We show that significant portions of the parameter space are excluded when the current LHC data is utilized effectively. We find that only $U_1$ and $V_2$ can explain the observed positive shift in $(a_{\mu }^{\exp }-a_{\mu }^{\mathrm{SM}})$ through a lepton chirality-flipping contribution with $\mathcal{O}(1)$ LQ-quark-lepton coupling. We also see how these two LQs can fit the electron dipole moment and atomic parity violation measurements. We find that the current electric dipole moment measurements of the muon cannot restrain the LQ-quark-lepton couplings within perturbative regions.

New gauge forces can play an important role in the evolution of the early Universe. In this work we investigate the cosmological implications of a pure Yang-Mills dark sector that is dominantly populated after primordial inflation. Such a dark sector takes the form of a bath of dark gluons at high temperatures, but confines at lower temperatures to produce a spectrum of dark glueballs. These glueballs then undergo a freeze-out process such that the remnant population is nearly completely dominated by the lightest state. To reproduce the observed cosmology, this lightest glueball species must decay to the Standard Model to repopulate and reheat it. At leading order, this can occur through a connector operator of dimension six. In contrast, other glueballs can be parametrically long lived or stable, and remain as contributors to dark matter or modify the observed cosmology through their later decays. In this work we study the evolution of such dark sectors in detail. We demonstrate that stable remnant glueballs can produce the measured dark matter abundance. We also derive broad constraints on non-Abelian dark sectors from overproduction of remnant glueballs when they are stable or from their destructive impact when they are able to decay.

We propose a simple model in the type-III seesaw framework to explain the neutrino mass, asymmetric dark matter (DM), and baryon asymmetry of the Universe. We extend the Standard Model with a vectorlike singlet lepton ($\chi$) and a hypercharge zero scalar triplet ($\mathrm{\Delta }$) in addition to three hypercharge zero triplet fermions (${\mathrm{\Sigma }}_i,i=1$, 2, 3). A $Z_2$ symmetry is imposed under which $\chi$ and $\mathrm{\Delta }$ are odd, while all other particles are even. As a result, the lightest $Z_2$ odd particle $\chi$ behaves as a candidate of DM. In the early Universe, the $CP$-violating out-of-equilibrium decay of heavy triplet fermions to the Standard Model lepton ($L$) and Higgs ($H$) generate a net lepton asymmetry, while that of triplet fermions to $\chi$ and $\mathrm{\Delta }$ generate a net asymmetric DM. The lepton asymmetry is converted to the required baryon asymmetry of the Universe via the electroweak sphalerons, while the asymmetry in $\chi$ remains as a DM relic that we observe today. We introduce a singlet scalar $\mathrm{\Phi }$, with mass $M_{\mathrm{\Phi }}<M_{\chi }$, which not only assists to deplete the symmetric component of $\chi$ through the annihilation process $\overline{\chi }\chi \to \mathrm{\Phi }\mathrm{\Phi }$, but also paves a path to detect DM $\chi$ at direct search experiments through $\mathrm{\Phi }-H$ mixing. The electroweak symmetry breaking induces a nonzero vacuum expectation value to $\mathrm{\Delta }$, which leads to an unstable asymmetric DM ranging from a few MeV to hundreds of GeV. We then explore the displaced vertex signatures of the charged components of the scalar triplet $\mathrm{\Delta }$ at colliders.

The Froggatt-Nielsen (FN) mechanism is an elegant solution to the flavor problem. In its minimal application to the quark sector, the different quark types and generations have different charges under a $U(1{)}_X$ flavor symmetry. The SM Yukawa couplings are generated below the flavor breaking scale with hierarchies dictated by the quark charge assignments. Only a handful of charge assignments are generally considered in the literature. We analyze the complete space of possible charge assignments with $|X_{q_i}|\le 4$ and perform both a set of Bayesian-inspired numerical scans and an analytical spurion analysis to identify those charge assignments that reliably generate SM-like quark mass and mixing hierarchies. The resulting set of top-20 flavor charge assignments significantly enlarges the viable space of FN models but is still compact enough to enable focused phenomenological study. We then apply our numerical methodology to demonstrate that these distinct charge assignments result in the generation of correlated flavor-violating four-quark operators characterized by significantly varied strengths, potentially differing substantially from the possibilities previously explored in the literature. Future precision measurement of $\mathrm{\Delta }F=2$ observables, along with increasingly accurate SM predictions, may therefore enable us to distinguish among otherwise equally plausible FN charges, thus shedding light on the UV structure of the flavor sector.

Below the electroweak scale, new physics that violates the lepton number in two units ($\mathrm{\Delta }L=2$) and is mediated by heavy particle exchange can be parametrized by a dimension-nine low-energy effective Lagrangian. Operators in this Lagrangian involving first-generation quarks and leptons contribute to the short-range mechanism of neutrinoless double beta decay ($0\nu \beta \beta$) and therefore they are strongly constrained. On the other hand, operators with other quark and lepton families are bounded by the nonobservation of different lepton number violating meson and tau decays, such as $M_1^{-}\to M_2^{+}{\ell }_1^{-}{\ell }_2^{-}$ and ${\tau }^{-}\to {\ell }^{+}{M}_1^{-}{M}_2^{-}$. In this work, we calculate renormalization-group-evolution (RGE)-improved bounds on the Wilson coefficients involved in these decays. We calculate QCD corrections to the dimension-nine operator basis and find RGE matrices that describe the evolution of the Wilson coefficients across different energy scales. Unlike the running of operators involved in $0\nu \beta \beta$ decay, the general flavor structure leads to the mixing of not only different Lorentz structures but also of different quark-flavor configurations. Additionally, operators that vanish for the identical lepton case need to be added to the operator basis. We find new constraints on previously unbounded operators and the enhancement of bounds for specific Wilson coefficients. We also find new bounds coming from the mixing between operators with different quark-flavor configurations.

We develop a bottom-up holographic model that provides the dual description of a strongly coupled field theory, in which the spontaneous breaking of an approximate global symmetry yields the $SO(5)/SO(4)$ coset relevant to minimal composite-Higgs models. The gravity background is completely regular and smooth, and has an end of space that mimics confinement on the field theory side. We add to the gravity description a set of localized boundary terms, that introduce additional symmetry-breaking effects, capturing those that would result from coupling the dual strongly coupled field theory to an external, weakly coupled sector. Such terms encapsulate the gauging of a subgroup of the global $SO(5)$ symmetry of the dual field theory, as well as additional explicit symmetry-breaking effects. We show how to combine spurions and gauge fixing and how to take the appropriate limits, so as to respect gauge principles and avoid violations of unitarity. The interplay of bulk and boundary-localized couplings leads to the breaking of the $SO(5)$ symmetry to either its $SO(4)$ or $SO(3)$ subgroup, via vacuum misalignment. In field theory terms, the model describes the spontaneous breaking of a $SO(4)$ gauge symmetry to its $SO(3)$ subgroup. We expose the implications of the Higgsing phenomenon by computing the spectrum of fluctuations of the model, which we interpret in four-dimensional field-theory terms, for a few interesting choices of parameters. We conclude by commenting on the additional steps needed to build a realistic composite Higgs model.