Thu·Feb 1, 2024Thursday·February 1, 2024

1. 01*

   Probing the interior of Earth using oscillating neutrinos at INO-ICAL

   Anil Kumar🇮🇳 · Anuj Kumar Upadhyay🇮🇳 · Sanjib Kumar Agarwalla🇮🇳 · Amol Dighe🇮🇳

   Atmospheric neutrinos offer the possibility of exploring the internal structure of Earth. This information is complementary to the traditional probes of seismic and gravitational studies. While propagating through Earth, the multi-GeV neutrinos encounter the Earth's matter effects due to the coherent forward scattering with the ambient electrons, which alters the neutrino oscillation probabilities. We present how well an atmospheric neutrino oscillation experiment like the 50 kt Iron Calorimeter (ICAL) detector at India-based Neutrino Observatory would validate the presence of Earth's core, measure the location of the core-mantle boundary (CMB), and probe the dark matter (DM) inside the Earth in a unique way through Earth matter effects in neutrino oscillations. Owing to good angular resolution, ICAL can observe the core-passing neutrinos efficiently. Due to its magnetized setup, it would be able to observe neutrinos and antineutrinos separately. With 500 kt$\cdot$yr exposure, the presence of Earth's core can be independently confirmed at ICAL with a median $\Delta {\chi }^2$ of 7.45 (4.83) for normal (inverted) mass ordering. With 1000 kt$\cdot$yr exposure, ICAL would be able to locate the CMB with a precision of about $\pm$ 250 km at $1\sigma$. It would also be sensitive to the possible presence of dark matter with 3.5% of the mass of Earth at $1\sigma$. The charge identification capability of ICAL would play an important role in achieving these precisions.

   hep-phhep-exphysics.ins-detPoS(2024)·0 citations
2. 02*

   Heavy flavor production under a strong magnetic field

   Shile Chen🇨🇳 · Jiaxing Zhao🇫🇷 · Pengfei Zhuang🇨🇳

   The magnetic field created in high energy nuclear collisions will affect the dynamical processes in the QCD medium, especially the heavy quark production that happens in the initial stage of the collisions. We calculate in a strong magnetic field the heavy quark production cross section for the elementary process gg {\rightarrow} Q{\bar Q} at leading order and the corresponding transverse momentum distribution in nucleus-nucleus collisions. In comparison to the QED process, the heavy quark production is dominated by the unique QCD channel with gluon self-interaction. Due to the dimension reduction of quark phase space in a strong magnetic field, the production is concentrated in a very narrow energy region above the threshold. Since the translation invariance is broken, the production becomes anisotropic in magnetic field.

   hep-phnucl-thJHEP(2024)·7 citations
3. 03*

   New Constraints on Gauged U(1)${}_{L_{\mu }-L_{\tau }}$ Models via $Z-Z^{\prime }$ Mixing

   Kento Asai🇯🇵 · Coh Miyao🇯🇵 · Shohei Okawa🇪🇸 · Koji Tsumura🇯🇵

   It is known that the model based on U(1)${}_{L_{\mu }-L_{\tau }}$ gauge symmetry can explain not only the discrepancy between the measured value of muon $g-2$ and the theoretical prediction, but also the structure of the neutrino mass and mixings. We revisit the analysis of the mass matrix structure in the minimal U(1)${}_{L_{\mu }-L_{\tau }}$ models based on the latest experimental result, where the minimal stands for the symmetry breaking caused only by a single scalar field. We find that the model called type $2_{+1}$, where an SU(2)${}_L$ doublet scalar ${\Phi }_{+1}$ with the U(1)${}_{L_{\mu }-L_{\tau }}$ charge $+1$ and the hypercharge $+1/2$, predicts the ${\mathbf{B}}_3$ texture and is marginally acceptable under the current neutrino oscillation data and cosmological observation. When the U(1)${}_{L_{\mu }-L_{\tau }}$ gauge symmetry is broken by the vacuum expectation value of the standard model non-singlet representation such as ${\Phi }_{+1}$, there are additional contributions to the flavor-changing meson decay process and atomic parity violation via the $Z-Z^{\prime }$ mixing. We newly evaluate the model-dependent constraints on the model and conclude that the type $2_{+1}$ model is robustly ruled out. The model is extended to have an additional vacuum expectation value of a standard model singlet scalar in order to avoid the stringent constraint from the flavor-changing meson decay. Finally, we find the allowed range of the ratio of these vacuum expectation values.

   hep-phJHEP(2024)·5 citations
4. 04*

   Exclusive photoproduction of a photon-meson pair: A new class of observables to probe GPDs

   Goran Duplančić🇭🇷 · Saad Nabeebaccus🇫🇷 · Kornelija Passek-K.🇭🇷 · Bernard Pire🇫🇷 · Jakob Schönleber · Lech Szymanowski🇵🇱 · Samuel Wallon🇫🇷

   We discuss the exclusive photoproduction of a photon-meson pair with large $p_T$ as a channel to probe generalised parton distributions (GPDs). Like other $2\to 3$ exclusive processes, this channel allows us to better study the $x$-dependence of GPDs, in contrast to $2\to 2$ processes such as Deeply Virtual Compton Scattering (DVCS) which give only "moment-type" information. Moreover, it also gives the possibility to access, at leading twist, the chiral-odd GPDs, which are still completely unknown experimentally. In the first part of these proceedings, we present the computation of the amplitude at leading order and leading twist, for charged pions, and rho mesons of any charge and polarisation. These processes are sensitive to quark GPDs only. We also discuss the possibility of measuring such processes at various experiments, namely JLab, COMPASS, future EIC and LHC in ultra-peripheral collisions. In particular, in collider experiments, the dependence of GPDs at small skewness $(<10^{-3})$ can be extracted. For the second part, we report on our recent work on the exclusive photoproduction of ${\pi }^0\gamma$ pair, which, in addition to a quark GPD channel, also has a contribution from gluon GPDs. In the latter case, we demonstrate that a collinear factorisation of the process fails, due to the presence of a Glauber pinch. Our findings also imply that other similar processes, like ${\pi }^{0}N\to \gamma \gamma N$ also suffer from the same issue. On the other hand, we stress that the processes discussed earlier, which are sensitive to the quark GPD channels only, are safe from these factorisation breaking effects.

   hep-phhep-exnucl-exnucl-thPoS(2024)·4 citations
5. 05*

   PartonDensity.jl: a novel parton density determination code

   Francesca Capel🇩🇪 · Ritu Aggarwal🇮🇳 · Michiel Botje🇳🇱 · Allen Caldwell🇩🇪 · Oliver Schulz🇩🇪 · Andrii Verbytskyi🇩🇪

   We introduce our novel Bayesian parton density determination code, PartonDensity.jl. The motivation for this new code, the framework and its validation are described. As we show, PartonDensity.jl provides both a flexible environment for the determination of parton densities and a wealth of information concerning the knowledge update provided by the analyzed data set.

   hep-phhep-exPRD(2024)·7 citations
6. 06*

   Electromagnetic form factors of the transition from the Delta to the nucleon

   Moh Moh Aung (Suranaree U. of Tech., Uppsala U.)🇹🇭 · Stefan Leupold (Uppsala U.)🇸🇪 · Elisabetta Perotti (Uppsala U.)🇸🇪 · Yupeng Yan (Suranaree U. of Tech.)🇹🇭

   The low-energy electromagnetic form factors of the $\Delta$(1232)-to-nucleon transition are derived combining dispersion theory techniques and chiral perturbation theory. The form factors are expressed in terms of the well-understood pion vector form factor and pion-baryon scattering amplitudes. Nucleon and Delta exchange terms and contact terms constitute the input for these pion-baryon amplitudes. The framework is formulated for all form factors. When comparing to experimental data in the spacelike region of $e^{-}N\to e^{-}\Delta$ scattering, the focus lies on the numerically dominant magnetic dipole transition form factor. Fitting two subtraction constants (one for the scattering amplitude, one for the form factor) yields a very good description of this dominant form factor up to photon virtualities of about 0.6 GeV. After determining the subtraction constants in the spacelike region and at the photon point, respectively, predictions for the timelike region of Dalitz decays $\Delta \to N{e}^{+}{e}^{-}$ are presented.

   hep-phnucl-thPRD(2025)·8 citations
7. 07*

   Revisiting Trimaximal TM2 mixing in two $A_4$ modular symmetries

   Han Zhang🇨🇳 · Ye-Ling Zhou🇨🇳

   We discuss a minimal lepton flavour model with two modular $A_4$ symmetries, one acting on neutrinos and the other acting on charged leptons. Two corresponding moduli fields are restricted at stabilisers. To avoid vanishing or degenerate lepton masses, the stabiliser in the charged lepton sector always preserves a $Z_3$ symmetry, and that in the neutrino preserves a $Z_2$ symmetry. By scanning all viable stabilisers, a unique Trimaximal TM2 mixing is predicted. However, the prediction of the lightest neutrino mass and the mass parameter in neutrinoless double beta decay, as well as two Majorana phases, are different and classified into three cases.

   hep-phInt.J.Mod.Phys.A(2024)·5 citations
8. 08*

   On the breakdown of eikonal approximation and survival of Reggeization in presence of dimension-5 Higgs-gluon coupling

   Michael Fucilla🇫🇷 · Maxim A. Nefedov🇫🇷 · Alessandro Papa🇮🇹

   We consider the one-loop effective vertex for the interaction of a gluon with a Reggeized gluon and a Higgs boson in the infinite-top-mass limit, which is described by a dimension-5 non-renormalizable operator. This vertex enters the calculation of differential cross sections for the forward inclusive production of a Higgs boson in high-energy proton-proton collisions, possibly in association with a backward jet or identified hadron, in a framework where next-to-leading logarithms of the energy are resummed to all orders. The effective vertex is extracted from the high-energy behavior of two-to-two amplitudes for the Higgs production in parton-parton collisions and relies on the validity of the Regge form for these amplitudes. We find that the usual eikonal approximation (Gribov prescription) for the Regge limit and the known region-expansion technique in this limit lead to an incomplete result for the amplitude. The discrepancy is traced back to the non-renormalizable nature of the involved operator. However, the Regge limit of the exact QCD amplitude agrees with the Regge-pole exchange form at one loop, nontrivially supporting the Reggeization hypothesis.

   hep-phhep-thJHEP(2024)·7 citations
9. 09*

   Deconfinement transition within the Curci-Ferrari model -- Renormalization scale and scheme dependences

   V. Tomas Mari Surkau🇫🇷 · Urko Reinosa🇫🇷

   We analyze the confinement/deconfinement transition of pure Yang-Mills theories within the framework of the center-symmetric Landau gauge supplemented by a Curci-Ferrari mass term that models the effect of the associated Gribov copies in the infrared. In addition to providing details for earlier one-loop calculations in that framework, we explore how the results depend on the renormalization scale and/or on the renormalization scheme. We find that the predicted values for the transition temperatures of SU($2$) and SU($3$) Yang-Mills theories are similar in both schemes and are little sensitive to the renormalization scale $\mu$ over a wide range of values including the standard range $\mu \in [\pi T,4\pi T]$. These values are also close both to those obtained from a minimal sensitivity principle and to those of lattice simulations, especially in the SU($3$) case. These results further confirm the good behavior of perturbative calculations within the Curci-Ferrari model and support the adequacy of the latter as an effective description of Yang-Mills theories in the infrared. We perform a similar analysis for the spinodal temperatures in the SU($3$) case and for the Polyakov loop, the order parameter associated to the breaking of center symmetry.

   hep-phhep-thPRD(2024)·10 citations
10. 10*

    Spin-1 Glueballs in the Witten-Sakai-Sugimoto Model

    Florian Hechenberger🇦🇹 · Josef Leutgeb🇦🇹 · Anton Rebhan🇦🇹

    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 $K_1(1400)K^{\ast }$ 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.

    hep-phPRD(2024)·9 citations
11. 11*

    Redefining Higgs interactions at the TeV scale

    Rafael L. Delgado🇪🇸 · Raquel Gómez-Ambrosio🇮🇹 · Javier Martínez-Martín🇪🇸 · Alexandre Salas-Bernárdez🇪🇸 · Juan J. Sanz-Cillero🇪🇸

    We present a field redefinition that simplifies the Higgs Effective Field Theory Lagrangian for the Electroweak Symmetry Breaking Sector. This simplification produces the same on-shell scattering amplitudes while greatly reducing the number of contributing Feynman diagrams for $\omega \omega \to n\times h$ processes (which approximate the $W_L{W}_L\to n\times h$ amplitudes at the TeV scale by means of the Equivalence Theorem).

    hep-phPoS(2024)·0 citations
12. 12*

    Short- vs. long-distance physics in $B\to K^{(\ast )}{\ell }^{+}{\ell }^{-}$: a data-driven analysis

    Marzia Bordone🇨🇭 · Gino isidori🇨🇭 · Sandro Mächler🇮🇹 · Arianna Tinari🇨🇭

    We analyze data on $B\to K{\mu }^{+}{\mu }^{-}$ and $B\to K^{\ast }{\mu }^{+}{\mu }^{-}$ decays in the whole dilepton invariant mass spectrum with the aim of disentangling short- vs. long-distance contributions. The sizable long-distance amplitudes from $c\bar{c}$ narrow resonances are taken into account by employing a dispersive approach. For each available $q^2=m_{\mu \mu }^2$ bin and each helicity amplitude an independent determination of the Wilson coefficient $C_9$, describing $b\to s{\ell }^{+}{\ell }^{-}$ transitions at short distances, is obtained. The consistency of the $C_9$ values thus obtained provides an a posteriori check of the absence of additional, sizable, long-distance contributions. The systematic difference of these values from the Standard Model expectation supports the hypothesis of a non-standard $b\to s{\mu }^{+}{\mu }^{-}$ amplitude of short-distance origin.

    hep-phEPJC(2024)·56 citations
13. 13*

    Bubble dynamics at the electroweak scale

    Andrea Guiggiani🇮🇹

    The dynamics of bubbles nucleated during a first-order phase transition is controlled by the non-equilibrium fluctuations generated by the traveling domain wall. An accurate modelling of the out-of-equilibrium properties of the plasma is necessary for the characterization of the phase transition relics, such as the signal of gravitational waves. In this thesis we provide a solution to the Boltzmann equation that describes the plasma fluctuations without imposing any ansatz on the perturbation by devising a new spectral method that leverages on the rotational invariance of the collision operator. This allows for a robust and fast computation of the terminal velocity of the wall. We then compare our results with the previous approaches in the literature finding important quantitative and qualitative differences. We also employ our method to determine the terminal velocity of the wall for two benchmark configurations in the singlet extended Standard Model. We finally assess the impact of different approximations and we find that the most important source of uncertainty is given by the infrared modes of the electroweak gauge bosons.

    hep-ph3 citations
14. 14*

    Diffuse Axion Background

    Joshua Eby🇸🇪 · Volodymyr Takhistov🇯🇵

    Relativistic axions can be readily produced in a broad variety of transient sources, such as axion star bosenova explosions, supernovae or even evaporating primordial black holes. We develop a general framework describing the resulting persistent diffuse axion background (D$a$B) due to accumulated axions from historic transient events. We derive strong constraints on the D$a$B flux from light axions $m\lesssim 10^{-3}\mathrm{eV}$ emitted from sources with energies $\omega \gtrsim \mathrm{MeV}$ considering the non-observation of excess photons associated with axion-photon coupling from experiments, including COMPTEL, NuSTAR, XMM-Newton, INTEGRAL, EGRET and Fermi. Future searches in experiments such as SKA, JWST, XRISM, Vera C. Rubin Observatory, AMEGO/e-ASTROGAM will allow probing D$a$B and associated axion-photon couplings with unprecedented sensitivity covering a wide range of possible source energies as low as $0.1\mu$eV and multiple decades in axion masses. We highlight the differences between astrophysical and dark sector sources of D$a$B. Further, we discuss complementarity with direct detection as well as prospects for other D$a$B searches. Our analysis demonstrates that D$a$B can act as a promising probe of populations of axion emission sources as well as emission mechanisms.

    hep-phastro-ph.COastro-ph.HEhep-ex24 citations
15. 15*

    Explaining the $\gamma \gamma +X$ Excesses at $\approx$151.5 GeV via the Drell-Yan Production of a Higgs Triplet

    Saiyad Ashanujjaman🇨🇳 · Sumit Banik🇨🇭 · Guglielmo Coloretti🇨🇭 · Andreas Crivellin🇨🇭 · Siddharth P. Maharathy🇮🇳 · Bruce Mellado🇿🇦

    The multi-lepton anomalies and searches for the associated production of a narrow resonance indicate the existence of a $\approx$151 GeV Higgs with a significance of $>5\sigma$ and $>3.9\sigma$, respectively. On the one hand, these anomalies require a sizable branching fraction of the new scalar to $WW$, while on the other hand, no $ZZ$ signal at this mass has been observed. This suggests that the new boson is the neutral component of an $SU(2{)}_L$ triplet with zero hypercharge. This field leads to a positive definite shift in the $W$ mass, as preferred by the current global fit, and is produced via the Drell-Yan process $pp\to W^{\ast }\to {\Delta }^0{\Delta }^{\pm }$. We use the side-bands of the ATLAS analysis \cite{ATLAS:2023omk} of the associated production of the Standard Model Higgs in the di-photon channel to search for this production mode of the triplet. Since the dominant decays of ${\Delta }^{\pm }$ depend only on its mass, the effect in the 22 signal categories considered by ATLAS is completely correlated. We find that the ones most sensitive to the Drell-Yan production of the triplet Higgs show consistent excesses at a mass of $\approx$151.5 GeV. Combining these channels in a likelihood ratio test, a non-zero Br$[{\Delta }^0\to \gamma \gamma ]=0.66\%$ is preferred by $\approx$3$\sigma$, supporting our conjecture.

    hep-phhep-exPLB(2025)·22 citations
16. 16*

    Leptonic neutral-current probes in a short-distance DUNE-like setup

    Salvador Centelles Chuliá🇩🇪 · O. G. Miranda🇲🇽 · Jose W.F. Valle🇪🇸

    Precision measurements of neutrino-electron scattering may provide a viable way to test the non-minimal form of the charged and neutral current weak interactions within a hypothetical near-detector setup for the Deep Underground Neutrino Experiment (DUNE). Although low-statistics, these processes are clean and provide information complementing the results derived from oscillation studies. They could shed light on the scale of neutrino mass generation in low-scale seesaw schemes.

    hep-phhep-exPRD(2024)·6 citations
17. 17*

    Non-perpetual Eternal Inflation and the Emergent de Sitter Swampland Conjecture

    Omer Guleryuz🇹🇷

    We introduce a novel correlation, $n_s$ - $\Delta N$, connecting CMB parameters to the required total e-folds for eternal inflation. This correlation provides a robust tool for evaluating eternal (string) inflation models using CMB data and explores the impact of quantum fluctuations on non-attractor phases. By generalizing eternal inflation criteria, our parameterization simplifies rigorous testing of predictions and reveals a link between refined de Sitter conjecture parameters and the eternal nature of the cosmic landscape. This points to a general tendency towards eternal behavior in low-energy effective field theories within the landscape, opening the possibility for our cosmic stage to potentially embrace a 'multiverse' scenario.

    ↳ hep-thgr-qchep-phEPJC(2024)·3 citations
18. 18*

    Toward quantum tunneling from excited states: Recovering imaginary-time instantons from a real-time analysis

    Thomas Steingasser🇺🇸 · David I. Kaiser🇺🇸

    We revisit the path integral description of quantum tunneling and lay the groundwork for its generalization to excites states through real-time path integral techniques. For clarity, we focus on the simple toy model of a point particle in a double-well potential, for which we perform all steps explicitly. Instead of performing the familiar Wick rotation from physical to imaginary time -- which is inconsistent with the requisite boundary conditions when treating tunneling from states other than the false vacuum -- we regularize the path integral by adding an infinitesimal complex contribution to the Hamiltonian, while keeping time strictly real. We find that this gives rise to a complex stationary-phase solution, in agreement with recent insights from Picard-Lefshitz theory. We then show that there exists a class of analytic solutions for the corresponding equations of motion, which can be made to match the appropriate boundary conditions in the physically relevant limits of a vanishing regulator and an infinite physical time. We provide a detailed discussion of this non-trivial limit. We find that, for systems without an explicit time-dependence, our approach reproduces the picture of an instanton-like solution defined on a finite Euclidean-time interval. Lastly, we discuss the generalization of our approach to broader classes of systems, for which it serves as a reliable framework for high-precision calculations.

    ↳ hep-thhep-phquant-phPRD(2025)·25 citations
19. 19*

    On a class of selection rules without group actions in field theory and string theory

    Justin Kaidi🇺🇸 · Yuji Tachikawa🇯🇵 · Hao Y. Zhang🇯🇵

    We discuss a class of selection rules which i) do not come from group actions on fields, ii) are exact at tree level in perturbation theory, iii) are increasingly violated as the loop order is raised, and iv) eventually reduce to selection rules associated with an ordinary group symmetry. We start from basic field-theoretical examples in which fields are labeled by conjugacy classes rather than representations of a group, and discuss generalizations using fusion algebras or hypergroups. We also discuss how such selection rules arise naturally in string theory, such as for non-Abelian orbifolds or other cases with non-invertible worldsheet symmetries.

    ↳ hep-thhep-phSciPost Phys.(2024)·59 citations
20. 20*

    Microlensing signatures of extended dark objects using machine learning

    Miguel Crispim Romão🇬🇧 · Djuna Croon🇬🇧

    This paper presents a machine learning-based method for the detection of the unique gravitational microlensing signatures of extended dark objects, such as boson stars, axion miniclusters and subhalos. We adapt MicroLIA, a machine learning-based package tailored to handle the challenges posed by low-cadence data in microlensing surveys. Using realistic observational timestamps, our models are trained on simulated light curves to distinguish between microlensing by point-like and extended lenses, as well as from other object classes which give a variable magnitude. We show that boson stars, examples of objects with a relatively flat mass distribution, can be confidently identified for $0.8\lesssim r/r_E\lesssim 3$. Intriguingly, we also find that more sharply peaked structures, such as NFW-subhalos, can be distinctly recognized from point-lenses under regular observation cadence. Our findings significantly advance the potential of microlensing data in uncovering the elusive nature of extended dark objects. The code and dataset used are also provided.

    ↳ astro-ph.COhep-phPRD(2024)·15 citations
21. 21*

    The Sun and core-collapse supernovae are leading probes of the neutrino lifetime

    Pablo Martínez-Miravé🇩🇰 · Irene Tamborra🇩🇰 · Mariam Tórtola🇪🇸

    The large distances travelled by neutrinos emitted from the Sun and core-collapse supernovae together with the characteristic energy of such neutrinos provide ideal conditions to probe their lifetime, when the decay products evade detection. We investigate the prospects of probing invisible neutrino decay capitalising on the detection of solar and supernova neutrinos as well as the diffuse supernova neutrino background (DSNB) in the next-generation neutrino observatories Hyper-Kamiokande, DUNE, JUNO, DARWIN, and RES-NOVA. We find that future solar neutrino data will be sensitive to values of the lifetime-to-mass ratio ${\tau }_1/m_1$ and ${\tau }_2/m_2$ of $\mathcal{O}(10^{-1}-10^{-2})$ s/eV. From a core-collapse supernova explosion at $10$ kpc, lifetime-to-mass ratios of the three mass eigenstates of $\mathcal{O}(10^5)$ s/eV could be tested. After $20$ years of data taking, the DSNB would extend the sensitivity reach of ${\tau }_1/m_1$ to $10^8$ s/eV. These results promise an improvement of about $6-15$ orders of magnitude on the values of the decay parameters with respect to existing limits.

    ↳ astro-ph.HEhep-phJCAP(2024)·25 citations
22. 22*

    Spontaneously Broken $(-1)$-Form U(1) Symmetries

    Daniel Aloni🇺🇸 · Eduardo García-Valdecasas🇺🇸 · Matthew Reece🇺🇸 · Motoo Suzuki🇯🇵

    Spontaneous breaking of symmetries leads to universal phenomena. We extend this notion to $(-1)$-form U(1) symmetries. The spontaneous breaking is diagnosed by a dependence of the vacuum energy on a constant background field $\theta$, which can be probed by the topological susceptibility. This leads to a reinterpretation of the Strong CP problem as arising from a spontaneously broken instantonic symmetry in QCD. We discuss how known solutions to the problem are unified in this framework and explore some, so far unsuccessful, attempts to find new solutions.

    ↳ hep-thhep-phSciPost Phys.(2024)·49 citations
23. 23*

    Chern-Simons bubbles: Lopsided false vacuum decay in axion electrodynamics

    Saquib Hassan🇬🇧 · John March-Russell🇬🇧 · Georges Obied🇬🇧

    We study axion electrodynamics, including the Chern-Simons interaction term, in the presence of parallel background electric and magnetic fields, as can for example occur in certain models of axion inflation and in the study of dyonic black holes. In this setup, we find a new back-reacted instanton solution which corresponds to the nucleation of an axion domain wall that screens the electromagnetic fields in a process analogous to Schwinger pair production, despite the absence of light charged particles. The full solution includes the effect of the Chern-Simons induced charges and currents on the axion domain wall arising from the Witten and Sikivie (anomalous Hall) effects, respectively. The Euclidean solution has a reduced $O(2)\times O(2)$ symmetry which describes the nucleation of a prolate bubble in its rest-frame. A unique feature of this solution is that the region of lower energy density is outside the bubble rather than inside. We also describe the time evolution of this initial configuration, showing how the bubble can become further elongated along the direction of the background electric and magnetic fields. We describe potential applications of this process in particle physics and cosmology.

    ↳ hep-thgr-qchep-ph8 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.