We consider the vector and the pseudovector glueball in the top-down holographic model of large-$N_c$ QCD of Witten and their decays into ordinary mesons described by the D8 brane construction due to Sakai and Sugimoto. At leading order, the relevant interactions are determined exclusively by the Chern-Simons action of the D8 branes and are thus rigidly connected to the chiral anomaly and the Wess-Zumino-Witten terms. As found in a previous study of the pseudovector glueball, which we revisit and complete, the resulting decay widths are surprisingly large, implying that both the pseudovector and the vector glueball are very broad resonances, with a conspicuous dominance of decays into $a_1\rho$ and $K_1(1400)K^{*}$ in the case of the vector glueball. We also obtain a certain weak mixing of vector glueballs with ordinary vector mesons, but we conclude that it does not provide an explanation for the so-called $\rho \pi$ puzzle in charmonium decays.

We discuss the possibility that threshold photoproduction of ${\eta }_{c,b}$ may be sensitive to the pseudovector $1^{+-}$ glueball exchange. We use the holographic construction to identify the pseudovector glueball with the Kalb-Ramond field, minimally coupled to bulk Dirac fermions. We derive the holographic C-odd form factor and its respective charge radius. Using the pertinent Witten diagrams, we derive and analyze the differential photoproduction cross section for ${\eta }_{c,b}$ in the threshold regime, including the interference from the dual bulk photon exchange with manifest vector dominance. The possibility of measuring this process at current and future electron facilities is discussed.

Strong transient magnetic fields are generated in noncentral relativistic heavy-ion collisions. These fields induce anisotropy within the strongly interacting medium that, in principle, can affect the thermodynamic properties of the medium. We use the Polyakov loop extended Nambu Jona-Lasinio model to study the quark matter subjected to an external magnetic field at vanishing baryon chemical potential (${\mathit{\mu }}_{\mathit{B}}$). We have estimated the degree of anisotropy in the speed of sound and isothermal compressibility within the magnetized quark matter as a function of temperature (T) and magnetic field (eB). This study helps us to understand the extent of directionality generated in the initial stages of noncentral collisions while giving us useful information about the system.

The entanglement entropy of a black hole and that of its Hawking radiation are expected to follow the so-called Page curve: After an increase in line with Hawking’s calculation, it is expected to decrease back to zero once the black hole has fully evaporated, as demanded by unitarity. Recently, a simple system-plus-bath model has been proposed which shows a similar behavior. Here, we make a general argument as to why such a Page-curve-like entanglement dynamics should be expected to hold generally for system-plus-bath models at small coupling and low temperatures, when the system is initialized in a pure state far from equilibrium. The interaction with the bath will then generate entanglement entropy, but it eventually has to decrease to the value prescribed by the corresponding mean-force Gibbs state. Under those conditions, it is close to the system ground state. We illustrate this on two paradigmatic open-quantum-system models, the exactly solvable harmonic quantum Brownian motion and the spin-boson model, which we study numerically. In the first example we find that the intermediate entropy of an initially localized impurity is higher for more localized initial states. In the second example, for an impurity initialized in the excited state, the Page time—when the entropy reaches its maximum—occurs when the excitation has half decayed.

In loop quantum cosmology, ambiguities in the Hamiltonian constraint can result in models with varying phenomenological predictions. In the homogeneous isotropic models, these ambiguities were settled, and the improved dynamics was found to be a unique and phenomenologically viable choice. This issue has remained unsettled on the inclusion of anisotropies, and in the Bianchi I model there exist two generalizations of isotropic improved dynamics. In the first of these, labeled as $\overline{\mu }$ quantization, the edge length of holonomies depends on the inverse of the directional scale factor. This quantization has been favored since it results in universal bounds on energy density and anisotropic shear, and can be viably formulated for noncompact as well as compact spatial manifolds. However, there exists an earlier quantization, labeled as ${\overline{\mu }}^{\prime }$ quantization, where edge lengths of holonomies depend on the inverse of the square root of directional triads. This quantization is also nonsingular and so far believed to yield a consistent physical picture for spatially compact manifolds. We examine the issue of the physical viability of these quantizations for different types of matter in detail by performing a large number of numerical simulations. Our analysis reveals certain limitations which have so far remained unnoticed. We find that while being nonsingular, the ${\overline{\mu }}^{\prime }$ quantization suffers from a surprising problem where one of the triad components and associated polymerized term retains Planckian character even at large volumes. As a result, not only is the anisotropic shear not preserved across the bounce, which is most highlighted in the vacuum case, but the universe can exhibit an unexpected cyclic evolution. These problematic features are absent from the $\overline{\mu }$ quantization leaving it as the only viable prescription for loop quantizing the Bianchi I model.

In ordinary thermodynamics, around first-order phase transitions, the intensive parameters such as temperature and pressure are automatically fixed to the phase transition point when one controls the extensive parameters such as total volume and total energy. From the microscopic point of view, the extensive parameters are more fundamental than the intensive parameters. Analogously, in conventional quantum field theory (QFT), coupling constants (including masses) in the path integral correspond to intensive parameters in the partition function of the canonical formulation. Therefore, it is natural to expect that, in a more fundamental formulation of QFT, coupling constants are dynamically fixed a posteriori, just as the intensive parameter in the microcanonical formulation. Here, we demonstrate that the automatic tuning of the coupling constants is realized at a quantum phase transition point at zero temperature, even when the transition is of higher order, due to the Lorentzian nature of the path integral. This naturally provides a basic foundation for the multicritical point principle. As a concrete toy model for solving the Higgs hierarchy problem, we study how the mass parameter is fixed in the ${\varphi }^4$ theory at the one-loop level in the microcanonical or further generalized formulation of QFT. We find that there are two critical points for the renormalized mass: zero and of the order of ultraviolet cutoff. In the former, the Higgs mass is automatically tuned to be zero and thus its fine-tuning problem is solved. We also show that the quadratic divergence is absent in a more realistic two-scalar model that realizes the dimensional transmutation. Additionally, we explore the possibility of fixing quartic coupling in ${\varphi }^4$ theory and find that it can be fixed to a finite value.

Lorentz violation (LV) is posited as a possible relic effect of quantum gravity at low energy scales. The standard model extension provides an effective field-theoretic framework for examining possible deviations attributed to LV. With their high observational accuracy, pulsars serve as ideal laboratories for probing LV. In the presence of LV, both the spin precession of solitary pulsars and orbital dynamics of binary pulsars would undergo modifications. Observations of pulse profiles and times of arrival of pulses allow for an in-depth investigation of these effects, leading to the establishment of strict limits on LV coefficients. We revisit the project of limiting local LV with updated pulsar observations. We employ a new parameter estimation method and utilize state-of-the-art pulsar timing observation data and get new limits on eight linear combinations of LV coefficients based on 25 tests from 12 different systems. Compared to previous limits from pulsars, precision has improved by a factor of 2–3. Additionally, we explore prospects for further improvements from pulsars. Simulation results indicate that more observations of spin precession in solitary millisecond pulsars could significantly enhance the accuracy of spatial LV coefficients, potentially by 3–4 orders of magnitude. As observational data accumulate, pulsars are anticipated to increasingly contribute to the tests of LV.

In general relativity, there are only two polarizations for gravitational waves. However, up to six polarizations are possible in a generic metric theory of gravity. Therefore, measuring the polarization content of gravitational waves provides an efficient way to test theories of gravity. We analyze the sensitivity of a next-generation ground-based detector network to nontensorial polarizations. We present our method to localize gravitational wave signals in the time-frequency domain and construct the model-independent null stream for events with known sky locations. We obtain results based on simulations of binary neutron star mergers in a six-detector network. For a single event at a luminosity distance $D_L=100\mathrm{Mpc}$, at $5\sigma$ confidence, the smallest amplitude for detection of scalar and vector modes relative to tensor modes are respectively $A_s=0.045$ and $A_v=0.014$. For multiple events in an averaged observing run of ten years, the detection limits at $5\sigma$ confidence are $A_s=0.05$ and $A_v=0.02$. If we are fortunate, a few strong events might significantly improve the limits.

New physics in the early Universe could lead to parity-violation in the late Universe, sourcing statistics whose sign changes under point reflection. The best constraints on such phenomena have come from the Planck temperature fluctuations; however, this is already cosmic-variance limited down to relatively small scales. Thus only small improvements are expected in the future. Here, we search for signatures of parity violation in the polarized cosmic microwave background, using the Planck PR4 $T$- and $E$-mode data. We perform both a simulation-based blind test for any parity-violating signal at $\ell <518$, and a targeted search for primordial $U(1)$ gauge fields (and the amplitudes of a generic collapsed model) at $\ell <2000$. In all cases, we find no evidence for new physics, with the model-independent test finding consistency with the $\mathrm{FFP}10/\mathrm{NPIPE}$ simulation suite at $(-)0.4\sigma$, and the gauge field test constraining the fractional amplitude of gauge fields during inflation to be below $6\times {10}^{-19}$ at 95% confidence level for a fiducial model. The addition of polarization data can significantly improve the constraints, depending on the particular model of primordial physics, and the bounds will tighten significantly with the inclusion of smaller-scale information.

This work compares cosmological matching conditions used in approximating generic pre-inflationary phases of the Universe. We show that the joining conditions for primordial scalar perturbations assumed by Contaldi et al. [J. Cosmol. Astropart. Phys. 07 (2003) 002] are inconsistent with the physically motivated Israel junction conditions; however, performing general relativistic matching with the aforementioned constraints results in unrealistic primordial power spectra. Eliminating the need for ambiguous matching, we look at an alternative semianalytic model for producing the primordial power spectrum allowing for finite duration cosmological phase transitions.

Recent studies indicate that thermally produced dark matter will form highly concentrated, low-mass cusps in the early universe that often survive until the present. While these cusps contain a small fraction of the dark matter, their high density significantly increases the expected $\gamma$-ray flux from dark matter annihilation, particularly in searches of large angular regions. We utilize 14 years of Fermi-LAT data to set strong constraints on dark matter annihilation through a detailed study of the isotropic $\gamma$-ray background, excluding with 95% confidence dark matter annihilation to $b\overline{b}$ final states for dark matter masses below 120 GeV.

Machine learning-based unfolding has enabled unbinned and high-dimensional differential cross section measurements. Two main approaches have emerged in this research area; one based on discriminative models and one based on generative models. The main advantage of discriminative models is that they learn a small correction to a starting simulation while generative models scale better to regions of phase space with little data. We propose to use Schrödinger bridges and diffusion models to create sbunfold, an unfolding approach that combines the strengths of both discriminative and generative models. The key feature of sbunfold is that its generative model maps one set of events into another without having to go through a known probability density as is the case for normalizing flows and standard diffusion models. We show that sbunfold achieves excellent performance compared to state of the art methods on a synthetic $Z+\text{jets}$ dataset.

Very recently, LHCb Collaboration observed that two new ${\mathrm{\Omega }}_c^0$ states decay into ${\mathrm{\Xi }}_c^{+}{K}^{-}$ with masses of about 3185 MeV and 3327 MeV. However, their spin-parity quantum numbers $J^P$ have not been determined. In this paper, we exploit the quark-diquark model, the linear Regge trajectory and the perturbation treatment method to analyze the mass spectra of the discovered experimental data for the singly heavy baryons ${\mathrm{\Sigma }}_c/{\mathrm{\Sigma }}_b$, ${\mathrm{\Xi }}_c^{\prime }/{\mathrm{\Xi }}_b^{\prime }$, and ${\mathrm{\Omega }}_c/{\mathrm{\Omega }}_b$. In addition, we further predict the mass spectra of several unobserved ${\mathrm{\Sigma }}_c/{\mathrm{\Sigma }}_b$, ${\mathrm{\Xi }}_c^{\prime }/{\mathrm{\Xi }}_b^{\prime }$, and ${\mathrm{\Omega }}_c/{\mathrm{\Omega }}_b$ baryons. In the case of the ${\mathrm{\Omega }}_c(3185{)}^0$ and ${\mathrm{\Omega }}_c(3327{)}^0$ states, we determine ${\mathrm{\Omega }}_c(3185{)}^0$ as $2S$ state and ${\mathrm{\Omega }}_c(3327{)}^0$ as $1D$ state with $J^P=1/2^{+}$ and $J^P=3/2^{+}$, respectively. An overall good agreement of the obtained predictions with available experimental data are found.

We have presented a detailed study about the prospects for the measurement of the top Yukawa coupling in the vector boson fusion production of a top quark pair at high energy muon colliders. By employing the effective $W$ approximation and the high energy limit for the helicity amplitudes of the subprocess $W^{+}{W}^{-}\to t\overline{t}$, we have derived the energy scaling of the statistical signal significance in the presence of the anomalous couplings by focusing on the interference term only. The sensitivity on the top Yukawa coupling decreases as the bin energy increases. For the anomalous triple gauge boson couplings and the gauge-boson-fermion couplings with $E^2$ energy growing behavior, the signal significance has mild increase at the beginning and starts to decrease for ${\widehat{s}}_{t\overline{t}}\sim 0.2s_{{\mu }^{+}{\mu }^{-}}$. The 95% CL on the anomalous top Yukawa coupling is projected to be 5.6% (1.7%) at a 10 (30) TeV muon collider, which is comparable to the sensitivity of 2% at the 100 TeV collider.

Belle II recently reported the new measurement $\mathcal{B}(B^{+}\to K^{+}\nu \overline{\nu })=(2.3\pm 0.7)\times {10}^{-5}$ [I. Adachi et al. (Belle-II Collaboration), arXiv:2311.14647] which is two times larger than their previous result (although consistent within errors) and about $2.7\sigma$ higher than the SM prediction. We reexamine new physics scenarios we discussed previously, which can enhance this rate to determine if they can accommodate the higher value reported in the new measurement. We use consistency with existing bounds on $B\to K^{*}\nu \overline{\nu }$, $b\to s{\ell }^{+}{\ell }^{-}$, $B\to D^{(*)}\ell \overline{\nu }$, and $B_s$ mixing to limit possible explanations for the excess. For the case of lepton flavor violating neutrino couplings, we find that only two leptoquarks remain viable requiring a large $C_{9^{\prime }}^{\tau \tau }=-C_{{10}^{\prime }}^{\tau \tau }$. For models with different types of light dark matter particle pairs (scalar, fermion, or vector), the preliminary $q^2$ distribution from Belle II, which shows that the excess appears mostly for bins with $3\le q^2\le 7{\mathrm{GeV}}^2$ [I. Adachi et al. (Belle-II Collaboration), arXiv:2311.14647], implies only the vector current operators with scalar or vector dark matter particles with masses in the hundreds of MeV can match the anomaly.

We consider machine learning techniques associated with the application of a boosted decision tree (BDT) to searches at the Large Hadron Collider (LHC) for pair-produced lepton partners which decay to leptons and invisible particles. This scenario can arise in the minimal supersymmetric Standard Model (MSSM), but can be realized in many other extensions of the Standard Model (SM). We focus on the case of intermediate mass splitting ($\sim 30\mathrm{GeV}$) between the dark matter (DM) and the scalar. For these mass splittings, the LHC has made little improvement over LEP due to large electroweak backgrounds. We find that the use of machine learning techniques can push the LHC well past discovery sensitivity for a benchmark model with a lepton partner mass of $\sim 110\mathrm{GeV}$, for an integrated luminosity of $300{\mathrm{fb}}^{-1}$, with a signal-to-background ratio of $\sim 0.3$. The LHC could exclude models with a lepton partner mass as large as $\sim 160\mathrm{GeV}$ with the same luminosity. The use of machine learning techniques in searches for scalar lepton partners at the LHC could thus definitively probe the parameter space of the MSSM in which scalar muon mediated interactions between SM muons and Majorana singlet DM can both deplete the relic density through dark matter annihilation and satisfy the recently measured anomalous magnetic moment of the muon. We identify several machine learning techniques which can be useful in other LHC searches involving large and complex backgrounds.

We carefully study the decay and reconstruction of long-lived particle (LLP) decays in the proposed MATHUSLA LLP detector for the HL-LHC. Our investigations are focused on three LLP benchmark models. MATHUSLA’s primary physics target is represented by hadronically decaying LLPs with mass above $\sim 10\mathrm{GeV}$, produced in exotic Higgs decays. We also investigate GeV-scale scalar and right-handed neutrino LLPs, which are the target of many other proposed experiments. We first introduce a public mathusla fastsim code to allow for efficient signal-only studies of LLP decays in MATHUSLA and general external LLP detectors. For each of our benchmark scenarios, we carefully simulate LLP production and decay, and make our simulation library publicly accessible for future investigations and comparisons with other experiments. We then systematically study the geometric acceptance of MATHUSLA for LLP decays in these scenarios, and present updated sensitivity projections that include these acceptances. Our results show that the idealized reach of MATHUSLA computed in earlier studies is mostly realized. We also investigate possible ways of increasing the signal acceptance using the inherent geometric flexibility of the FastSim, which will provide useful inputs for realistic experimental and engineering optimization of the detector in the future.

We calculate the contribution of gluons to single inclusive hadron production at next-to-leading order (NLO) accuracy in deep inelastic scattering (DIS) at small $x$ using the color glass condensate formalism. It is shown that the only divergence present is the standard collinear divergence, which is absorbed into scale evolution of quark-hadron fragmentation function. Our calculations are performed at finite $N_c$ and we provide general finite $N_c$ expressions for the structure of Wilson lines appearing in inclusive dihadron and single hadron production cross sections. We also comment on how one can obtain rapidity distribution of hadron multiplicities from our results.

Differential cross sections of the elastic pion-proton scattering are investigated at very small momentum transfer in a holographic QCD model, considering both the strong and Coulomb interaction in the Regge regime. The strong interaction is described by the Pomeron and Reggeon exchange, and the Coulomb interaction is characterized by the one photon exchange. The two interactions are linked through an interference term and we only need to determine a single adjustable parameter involved in this term. As to the parameters for the strong interaction, we can utilize the values determined in the previous studies. The differential cross sections can be predicted without any additional parameters, and it is shown that our predictions are consistent with the experimental data. We explicitly show the momentum transfer dependence for the interference effect. The energy dependence of the contribution ratios for each component is also discussed.