Effective Field Theory Research Articles

Radiative Corrections to Superallowed β Decays in Effective Field Theory

The accuracy of Vud determinations from superallowed β decays critically hinges on control over radiative corrections. Recently, substantial progress has been made on the single-nucleon, universal corrections, while nucleus-dependent effects, typically parametrized by a quantity δNS, are much less well constrained. Here, we lay out a program to evaluate this correction from effective field theory (EFT), highlighting the dominant terms as predicted by the EFT power counting. Moreover, we compare the results to a dispersive representation of δNS and show that the expected momentum scaling applies even in the case of low-lying intermediate states. Our EFT framework paves the way toward calculations of δNS and thereby addresses the dominant uncertainty in Vud. Published by the American Physical Society 2024

Exploring optimal sensitivity of lepton flavor violating effective couplings at the e+e− colliders

We analyze lepton flavor violation (LFV) using the Standard Model effective field theory (SMEFT) framework at the future lepton colliders. Our focus is on the associated production of tau lepton with electron/muon at the electron-positron (e+e−) colliders, related to four-Fermi SMEFT effective operators. In accordance with the upper limits on effective couplings from lepton flavor violating tau decays, we conduct a cut-based analysis to achieve sufficient signal significance. We utilize the optimal observable technique (OOT) to estimate the optimal sensitivity of the effective couplings. The impact of electron beam polarization and the interplay of signal and background in enhancing the optimal sensitivity of the effective couplings are discussed in detail. We find that the sensitivity of flavor-violating effective couplings is enhanced by order of one for 3 TeV center-of-mass (CM) energy and 1000 fb−1 integrated luminosity at the e+e− colliders. Published by the American Physical Society 2024

Bosonic multi-Higgs correlations beyond leading order

The production of multiple Higgs bosons at the LHC and beyond is a strong test of the mechanism of electroweak symmetry breaking. Taking inspiration from recent experimental efforts to move toward limits on triple-Higgs production at the Large Hadron Collider, we consider generic bosonic deviations of HH and HHH production from the Standard Model in the guise of Higgs effective field theory (HEFT). Including one-loop radiative corrections within the HEFT and going up to O(p4) in the momentum expansion, we provide a detailed motivation of the parameter range that the LHC (and future hadron colliders) can explore, through accessing nonstandard coupling modifications and momentum dependencies that probe Higgs boson nonlinearities. In particular, we find that radiative corrections can enhance the sensitivity to Higgs self-coupling modifiers and HEFT-specific momentum dependencies can vastly increase triple-Higgs production, thus providing further motivation to consider these processes during the LHC’s high-luminosity phase. Published by the American Physical Society 2024

Regularized-renormalized-resummed loop corrected power spectrum of non-singular bounce with Primordial Black Hole formation

AbstractWe present a complete and consistent exposition of the regularization, renormalization, and resummation procedures in the setup of having a contraction and then non-singular bounce followed by inflation with a sharp transition from slow-roll (SR) to ultra-slow roll (USR) phase for generating primordial black holes (PBHs). We consider following an effective field theory (EFT) approach and study the quantum loop corrections to the power spectrum from each phase. We demonstrate the complete removal of quadratic UV divergences after renormalization and softened logarithmic IR divergences after resummation and illustrate the scheme-independent nature of our renormalization approach. We further show that the addition of a contracting and bouncing phase allows us to successfully generate PBHs of solar-mass order, $$M_\textrm{PBH}\sim \mathcal{O}(M_{\odot })$$ M PBH ∼ O ( M ⊙ ) , by achieving the minimum e-folds during inflation to be $$\Delta N_{\textrm{Total}}\sim \mathcal{O}(60)$$ Δ N Total ∼ O ( 60 ) and in this process successfully evading the strict no-go theorem. We notice that varying the effective sound speed between $$0.88\leqslant c_{s}\leqslant 1$$ 0.88 ⩽ c s ⩽ 1 , allows the peak spectrum amplitude to lie within $$10^{-3}\leqslant A \leqslant 10^{-2}$$ 10 - 3 ⩽ A ⩽ 10 - 2 , indicating that causality and unitarity remain protected in the theory. We analyse PBHs in the extremely small, $$M_{\textrm{PBH}}\sim \mathcal{O}(10^{-33}-10^{-27})M_{\odot }$$ M PBH ∼ O ( 10 - 33 - 10 - 27 ) M ⊙ , and the large, $$M_{\textrm{PBH}}\sim \mathcal{O}(10^{-6}-10^{-1})M_{\odot }$$ M PBH ∼ O ( 10 - 6 - 10 - 1 ) M ⊙ , mass limits and confront the PBH abundance results with the latest microlensing constraints. We also study the cosmological beta functions across all phases and find their interpretation consistent in the context of bouncing and inflationary scenarios while satisfying the pivot scale normalization requirement. Further, we estimate the spectral distortion effects and shed light on controlling PBH overproduction.

Probing effective operators in single top quark production in association with a lepton-neutrino pair

We study single top quark production in association with a lepton-neutrino pair at the LHC within the framework of the Standard Model effective field theory (SMEFT). We focus on relevant two-quark-two-lepton operators (Olq3, Olequ1, and Olequ3). It is known that these operators have tiny effects on the inclusive cross section of standard model tW production and are thus typically ignored in the SMEFT searches. However, we show that by employing smart observables, such as mT2, the pp→tℓν process is significantly sensitive to these operators. We set the most stringent limit on the coupling strength of the Olq3 operator by reinterpreting the results of a search for new phenomena with two opposite-charge leptons, jets and missing transverse momentum at s=13 TeV performed by the ATLAS collaboration. The limits derived on the Olequ1 and Olequ3 operators are comparable to those obtained from probing EFT effects in pp→tt¯ℓν and pp→tt¯ℓℓ processes at the LHC. Consequently, we propose to include the effects of these three operators on the pp→tℓν process in future global SMEFT analyses to increase the sensitivity and to reduce possible degeneracies. Published by the American Physical Society 2024

Axion species scale and axion weak gravity conjecture-like bound

Abstract As a cutoff scale of quantum gravity, the species scale can be defined by the scale at which the perturbativity of the non-renormalizable gravitational interaction begins to break down. Since it is determined by the number of species in the effective field theory, we can find the close connection to the distance conjecture, which predicts the lowering of the cutoff at the asymptotic limit of the moduli space caused by the descent of a tower of states from UV. Meanwhile, the same kind of the cutoff scale can be obtained from any non-renormalizable interaction, in particular the interaction between the axion and the gauge field through the θF ∧ F term. Demanding this ‘axion species scale’ not to exceed the gravitational species scale, we obtain the bound (8π 2/g 2)f ≲ M Pl. This is quite similar to the axion weak gravity conjecture bound, but can be applied to any gauge as well as the string interactions which are relevant to towers of states. We also investigate the implications of the (axion) species scale and the axion weak gravity conjecture-like bound by considering the Peccei-Quinn charge reduction of black hole through the interaction between black hole and the string or wormhole.

Predicting the 21-cm field with a hybrid effective field theory approach

Predicting the 21-cm field with a hybrid effective field theory approach

Supergeometric quantum effective action

Supergeometric quantum field theories (SG-QFTs) are theories that go beyond the standard supersymmetric framework, since they allow for general scalar-fermion field transformations on the configuration space of a supermanifold, without requiring an equality between bosonic and fermionic degrees of freedom. After revisiting previous considerations, we extend them by calculating the one-loop effective action of minimal SG-QFTs that feature nonzero fermionic curvature in two and four spacetime dimensions. By employing an intuitive approach to the Schwinger–DeWitt heat-kernel technique and a novel field-space generalized Clifford algebra, we derive the ultraviolet structure of characteristic effective-field-theory (EFT) operators up to four spacetime derivatives that emerge at the one-loop order and are of physical interest. Upon minimizing the impact of potential ambiguities due to the so-called multiplicative anomalies, we find that the EFT interactions resulting from the one-loop supergeometric effective action are manifestly diffeomorphically invariant in configuration space. The extension of our approach to evaluating higher loops of the supergeometric quantum effective action is described. The emerging landscape of theoretical and phenomenological directions for further research of SG-QFTs is discussed. Published by the American Physical Society 2024

Effective theory tower for μ → e conversion

Abstract We present theoretical predictions for μ → e conversion rates using a tower of effective field theories connecting the UV to nuclear physics scales. The interactions in nuclei are described using a recently developed nonrelativistic effective theory (NRET) that organizes contributions according to bound nucleon and muon velocities, $$ {\overrightarrow{v}}_N $$ v → N and $$ {\overrightarrow{v}}_{\mu } $$ v → μ , with $$ \left|{\overrightarrow{v}}_N\right| $$ v → N >$$ \left|{\overrightarrow{v}}_{\mu}\right| $$ v → μ . To facilitate the top-down matching, we enlarge the set of Lorentz covariant nucleon-level interactions mapped onto the NRET operators to include those mediated by tensor interactions, in addition to the scalar and vector interactions already considered previously, and then match NRET nonperturbatively onto the Weak Effective Theory (WET). At the scale μ ≈ 2 GeV WET is formulated in terms of u, d, s quarks, gluons and photons as the light degrees of freedom, along with the flavor-violating leptonic current. We retain contributions from WET operators up to dimension 7, which requires the full set of 26 NRET operators. The results are encoded in the open-source Python- and Mathematica-based software suite MuonBridge, which we make available to the theoretical and experimental communities interested in μ → e conversion.

Stringy forces in the black hole interior

Effective field theories break down inside large black holes on macroscopic scales when tidal forces are string-sized. If r0 is the horizon radius and α′ is the square of the string scale, the 4D Schwarzschild interior is strongly curved at (r0α′)1/3. Infalling massless probes that reach this scale stretch and become excited strings. I generalize this picture for a wide class of black hole solutions in string theory. For the black hole dual to the large-N BFSS model in a thermal state, and denoting ℓP the Planck length, tidal forces are stringy at r0r0N1/3ℓP3/11\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {r}_0{\\left(\\frac{r_0}{N^{1/3}{\\ell}_P}\\right)}^{3/11} $$\\end{document}, which is greater than the scale where string perturbation theory breaks down for sufficiently large r0/ℓP. For 4D Kerr, there is a range of spin parameters for which the inner horizon is to the future of the scale of stringy curvature. These results specify the portion of black hole interior solutions where effective field theory can be used; beyond these scales, one must resort to other methods.

String loops and gravitational positivity bounds: imprint of light particles at high energies

Abstract We study loop corrections to positivity bounds on effective field theories in the context of 2 → 2 scattering in gravitational theories, in the presence of light particles. It has been observed that certain negative contributions at low energies are enhanced by inverse powers of a small mass m and are nontrivial to cancel against other low-energy contributions. These originate from near the forward limit of diagrams involving graviton exchange. We observe that scattering in this kinematics domain remains infrared-sensitive even at high center-of-mass energy. By considering a string-inspired model in which high-energy loops can be calculated using unitarity and Regge behavior of tree amplitudes, we uncover a natural mechanism through which 1/m-enhanced terms perfectly cancel between low and high energy contributions. This concretely explains possible positivity violations in the presence of gravity from the high-energy viewpoint.

Impurities with a cusp: general theory and 3d Ising

In CFTs, the partition function of a line defect with a cusp depends logarithmically on the size of the line with an angle-dependent coefficient: the cusp anomalous dimension. In the first part of this work, we study the general properties of the cusp anomalous dimension. We relate the small cusp angle limit to the effective field theory of defect fusion, making predictions for the first couple of terms in the expansion. Using a concavity property of the cusp anomalous dimension we argue that the Casimir energy between a line defect and its orientation reversal is always negative (“opposites attract”). We use these results to determine the fusion algebra of Wilson lines in N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 4 SYM as well as pinning field defects in the Wilson-Fisher fixed points. In the second part of the paper we obtain nonperturbative numerical results for the cusp anomalous dimension of pinning field defects in the Ising model in d = 3, using the recently developed fuzzy-sphere regularization. We also compute the pinning field cusp anomalous dimension in the O(N) model at one-loop in the ε-expansion. Our results are in agreement with the general theory developed in the first part of the work, and we make several predictions for impurities in magnets.

Pion photoproduction of nucleon excited states with Hamiltonian effective field theory

We refine our previous calculation of multipole amplitude E0+ for pion photoproduction process, γN→πN. The treatment of final-state interactions is based upon an earlier analysis of pion-nucleon scattering within Hamiltonian effective field theory, supplemented by incorporating contributions from the N*(1650) and the KΛ coupled channel. The contribution from the bare state corresponding to the N*(1650) significantly enhances our results. Additionally, we also compute the multipole amplitude M1−, which is of direct relevance to the Roper resonance. The results are comparable with other dynamical coupled-channel models, even though the contribution from the bare state (interpreted as a 2s excitation) in this channel is small because of its large mass. Published by the American Physical Society 2024

The g6 pressure of hot Yang-Mills theory: canonical form of the integrand

We present major progress towards the determination of the last missing piece for the pressure of a Yang-Mills plasma at high temperatures at order g6 in the strong coupling constant. This order is of key importance due to its role in resolving the long-standing infrared problem of finite-temperature field theory within a dimensionally reduced effective field theory setup. By systematically applying linear transformations of integration variables, or momentum shifts, we resolve equivalences between different representations of Feynman sum-integrals on the integrand level, transforming those into a canonical form. At the order g6, this results in reducing a sum of O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(100000) distinct sum-integrals which are produced from all four-loop vacuum diagrams down to merely 21. Furthermore, we succeed to map 11 of those onto known lower-loop structures. This leaves only 10 genuine 4-loop sum-integrals to be evaluated, thereby bringing the finalization of three decades of theoretical efforts within reach.

Frozen stars: Black hole mimickers sourced by a string fluid

The frozen star is a nonsingular, ultracompact object that, to an external observer, looks exactly like a Schwarzschild black hole, but with a different interior geometry and matter composition. The frozen star needs to be sourced by an extremely anisotropic fluid, for which the sum of the radial pressure and energy density is either vanishing or perturbatively small. Here, we show that this matter can be identified with the string fluid resulting from the decay of an unstable D-brane or a brane-antibrane system at the end of open-string tachyon condensation. The string fluid corresponds to flux tubes emanating from the center and ending at the Schwarzschild radius of the star. The effective Lagrangian for this fluid can be recast into a Born-Infeld form. When the fluid Lagrangian is coupled to that of Einstein’s gravity, the static, spherically symmetric solutions of the equations of motion are shown to be the same as those describing the frozen star model. Frozen stars can therefore be viewed as a gravitationally backreacted BIons model or that of gravitationally confined flux tubes. The Born-Infeld Lagrangian provides a complete set of equations that describe the dynamics of the frozen star in a generic state, which is not necessarily static nor spherically symmetric. Our framework therefore should allow a fully dynamical and out-of-equilibrium description of the frozen star model which will be relevant to gravitational waves observations of mergers of astrophysical black holes. Published by the American Physical Society 2024

Fractal subsystem symmetries, anomalies, boundaries, and effective field theory

Fractal subsystem symmetries, anomalies, boundaries, and effective field theory

Investigating tidal heating in neutron stars via gravitational Raman scattering

We present a scattering amplitude formalism to study the tidal heating effects of nonspinning neutron stars incorporating both worldline effective field theory and relativistic stellar perturbation theory. In neutron stars, tidal heating arises from fluid viscosity due to various scattering processes in the interior. It also serves as a channel for the exchange of energy and angular momentum between the neutron star and its environment. In the interior of the neutron star, we first derive two master perturbation equations that capture fluid perturbations accurate to linear order in frequency. Remarkably, these equations receive no contribution from bulk viscosity due to a peculiar adiabatic incompressibility which arises in stellar fluid for nonbarotropic perturbations. In the exterior, the metric perturbations reduce to the Regge-Wheeler equation which we solve using the analytical Mano-Suzuki-Takasugi method. We compute the amplitude for gravitational waves scattering off a neutron star, also known as gravitational Raman scattering. From the amplitude, we obtain expressions for the electric quadrupolar static Love number and the leading dissipation number to all orders in compactness. We then compute the leading dissipation number for various realistic equations of state and estimate the change in the number of gravitational-wave cycles due to tidal heating during inspiral in the LIGO-Virgo-KAGRA band. Published by the American Physical Society 2024

Phase transitions, critical behavior and microstructure of the FRW universe in the framework of higher order GUP

In this paper, we explore the phase transition, critical behavior and microstructure of the FRW in the framework of a new higher order generalized uncertainty principle (GUP). Our initial step involves deriving the equation of state by defining the work density W from GUP corrected Friedmann equations as the thermodynamic pressure P. Based on the modified equation of state, we conduct an analysis of the P−V phase transition in the FRW universe. Subsequently, we obtain the critical exponents and coexistence curves for the small and large phases of the FRW universe around the critical point. Finally, employing Ruppeiner geometry, we derive the thermodynamic curvature scalar RN, investigating its sign-changing curve and spinodal curve. The results reveal distinctive thermodynamic properties for FRW universes with positive and negative GUP parameters β. In the case of β>0, the phase transition, critical behavior and microstructure of FRW universe are like those of Van der Waals system and charged AdS. Conversely, for β<0, the results resemble those obtained through effective scalar field theory. These findings underscore the capacity of quantum gravity to induce phase transitions in the universe, warranting further in-depth exploration.

Axion and dark fermion electromagnetic form factors in superfluid He4

Condensed matter materials have shown great potential in searching for light dark matter (DM) via detecting the phonon or magnon signals induced by the scattering of DM off the materials. In this paper, we study the possibility of detecting electromagnetic form factors of fermionic DM and axionlike particles (ALPs) using superfluid He4. The phonon induced by a sub-GeV fermionic DM scattering off the superfluid can be described using the effective field theory with the interaction between DM and the bulk He4. Signals arising from the electromagnetic form factors of light DM in the presence of an external electric field are calculated. Projected constraints on the charge radius, anapole moment, and magnetic moment of the DM are derived with 1 kg·yr exposure. The phonon signal induced by the scattering of ALPs off the superfluid is also calculated, which can put competitive and the first direct detection bounds on ALP-photon-dark photon couplings in the projected experiments. Published by the American Physical Society 2024

The open effective field theory of inflation

Abstract In our quest to understand the generation of cosmological perturbations, we face two serious obstacles: we do not have direct information about the environment experienced by primordial perturbations during inflation, and our observables are practically limited to correlators of massless fields, heavier fields and derivatives decaying exponentially in the number of e-foldings. The flexible and general framework of open systems has been developed precisely to face similar challenges. Building on previous work, we develop a Schwinger-Keldysh path integral description for an open effective field theory of inflation, describing the possibly dissipative and non-unitary evolution of the Goldstone boson of time translations interacting with an unspecified environment, under the key assumption of locality in space and time. Working in the decoupling limit, we study the linear and interacting theory in de Sitter and derive predictions for the power spectrum and bispectrum that depend on a finite number of effective couplings organised in a derivative expansion. The smoking gun of interactions with the environment is an enhanced but finite bispectrum close to the folded kinematical limit. We demonstrate the generality of our approach by matching our open effective theory to an explicit model. Our construction provides a standard model to simultaneously study phenomenological predictions as well as quantum information aspects of the inflationary dynamics.