Effective Field Theory Approach Research Articles

Perturbation theory with dispersion and higher cumulants: Framework and linear theory

The authors develop an alternative perturbative approach to gravitational clustering and the large-scale structure. This approach is complementary to the effective field theory approach while being much more predictive and providing a more detailed understanding of mechanisms like the decoupling of nonlinear small-scale modes into dark matter halos where standard perturbation theory completely fails. This is an exciting step into the future of making predictions, especially in light of upcoming Stage IV experiments.

Perturbation theory with dispersion and higher cumulants: Nonlinear regime

The authors develop an alternative perturbative approach to gravitational clustering and the large-scale structure. This approach is complementary to the effective field theory approach while being much more predictive and providing a more detailed understanding of mechanisms like the decoupling of nonlinear small-scale modes into dark matter halos where standard perturbation theory completely fails. This is an exciting step into the future of making predictions, especially in light of upcoming Stage IV experiments.

DRalgo: A package for effective field theory approach for thermal phase transitions

DRalgo is an algorithmic implementation that constructs an effective, dimensionally reduced, high-temperature field theory for generic models. The corresponding Mathematica package automatically performs the matching to next-to-leading order. This includes two-loop thermal corrections to scalar and Debye masses as well as one-loop thermal corrections to couplings. DRalgo also allows for integrating out additional heavy scalars. Along the way, the package provides leading-order beta functions for general gauge-charges and fermion-families; both in the fundamental and in the effective theory. Finally, the package computes the finite-temperature effective potential within the effective theory. The article explains the theory of the underlying algorithm while introducing the software on a pedagogical level. Program summaryProgram title: Dimensional Reduction algorithm (DRalgo) 1.0CPC Library link to program files:https://doi.org/10.17632/k66j9vmh9r.1Developer's repository link:https://github.com/DR-algo/DRalgoLicensing provisions: GNU General Public License 3Programming language:MathematicaExternal routines/libraries:GroupMath [1]Nature of problem: Construction of high-temperature effective field theories for beyond the Standard Model physics.Solution method: Matching of n-point correlation functions using tensor-notation of couplings [2–6]Additional comments including restrictions and unusual features:Mathematica version 12 or above.

On the breakdown of space–time in general relativity

Based on the canonical quantization of d > 2-dimensional general relativity (GR) via the Dirac constraint formalism (also termed as ‘constraint quantization’), we propose the loss of covariance as a fundamental property of the theory. This breakdown occurs for the first-order Einstein–Hilbert action, whereby the loss of diffeomorphism invariance, besides first-class constraints, second-class constraints also exist leading to non-standard ghost fields that render the path integral non-covariant. We also attempt, for the first time, the canonical quantization via calculation of the path integral for the equivalent Hamiltonian formulation of GR, for which only first-class constraints exist. However, loss of covariance still occurs in this action due to loss of diffeomorphism invariance and structures arising from non-covariant constraints in the path integral. In contrast, we find that covariance as a symmetry is restored and quantization with perturbative calculations is possible in the weak limit of the gravitational field of these actions. Hence, we first establish, for the first time, that the breakdown in space–time is a property of GR itself as its limitation, indicating it to be an effective field theory (EFT). We further propose that the breakdown of space–time occurs as a non-perturbative feature of GR in the strong field limit of the theory. Besides GR, we also note that covariance is preserved when constraint quantization is conducted for non-Abelian gauge theories, such as the Yang–Mills theory. These findings are novel from a canonical gravity formalism and EFT approach, and are consistent with GR singularity theorems, yet are general and extend them, as the singularity theorems indicate breakdown at a strong field limit of GR in black holes. Our findings are in contrast to the asymptotic safety program. They support emergent theories of space–time and gravity, though are unique, as they do not require thermodynamics such as the entropic gravity program. From an EFT view, these indicate that new degrees of freedom and(or) principles in the non-perturbative sector of the full theory are a requirement, whereby covariance as a symmetry is broken in the high-energy (strong field) sector of GR.

Quench dynamics of the Kondo effect: Transport across an impurity coupled to interacting wires

We study the real-time dynamics of the Kondo effect after a quantum quench in which a magnetic impurity is coupled to two metallic Hubbard chains. Using an effective field theory approach, we find that for noninteracting electrons the charge current across the impurity is given by a scaling function that involves the Kondo time. In the interacting case, we show that the Kondo time decreases with the strength of the repulsive interaction and the time dependence of the current reveals signatures of the Kondo effect in a Luttinger liquid. In addition, we verify that the relaxation of the impurity magnetization does not exhibit universal scaling behavior in the perturbative regime below the Kondo time. Our results highlight the role of nonequilibrium dynamics as a valuable tool in the study of quantum impurities in interacting systems.

Effective two-body approach to the hierarchical three-body problem: Quadrupole to 1PN

Many binary systems of interest for gravitational-wave astronomy are orbited by a third distant body, which can considerably alter their relativistic dynamics. Precision computations are needed to understand the interplay between relativistic corrections and three-body interactions. We use an effective field theory approach to derive the effective action describing the long time-scale dynamics of hierarchical three-body systems up to 1PN quadrupole order. At this level of approximation, computations are complicated by the backreaction of small oscillations on orbital time-scales as well as deviations from the adiabatic approximation. We address these difficulties by eliminating the fast modes through the method of near-identity transformations. This allows us to compute for the first time the complete expression of the 1PN quadrupole cross-terms in generic configurations of three-body systems. We numerically integrate the resulting equations of motion and show that 1PN quadrupole terms can affect the long term dynamics of relativistic three-body systems.

Flows into de Sitter space from anisotropic initial conditions: An effective field theory approach

For decades, physicists have analyzed various versions of a ``cosmic no-hair'' conjecture, to understand under what conditions a spacetime that is initially spatially anisotropic and/or inhomogeneous will flow into an isotropic and homogeneous state. Wald's theorem, in particular, established that homogeneous but anisotropic spacetimes, if filled with a positive cosmological constant plus additional matter sources that satisfy specific energy conditions, will necessarily flow toward an (isotropic) de Sitter state at late times. In this paper we study the flow of homogeneous but anisotropic spacetimes toward isotropic states under conditions more general than those to which Wald's theorem applies. We construct an effective field theory (EFT) treatment for generic ``single-clock'' systems in anisotropic spacetimes---which are not limited to realizations compatible with scalar-field constructions---and identify fixed points in the resulting phase space. We identify regions of this phase space that flow to isotropic fixed points---including a de Sitter fixed point---even in the absence of a bare cosmological constant, and for matter sources that do not obey the energy conditions required for Wald's theorem. Such flows into de Sitter reveal the emergence of an effective cosmological constant.

Connecting b → sℓℓ with and

We discuss the consequences of deviations from the Standard Model observed in b → sμ + μ − transitions for flavour-changing neutral-current processes involving down-type quarks and neutrinos. We work within an effective field theory approach respecting the SM gauge symmetry, including right-handed currents, a flavour structure based on approximate U(2) symmetry, and assuming only SM-like light neutrinos. We discuss correlations among (hs = K, K*, Xs ), and branching ratios in the case of linear Minimal Flavour Violation and in a more general framework.

Radiation-reaction in the Effective Field Theory approach to Post-Minkowskian dynamics

We extend the Post-Minkowskian (PM) effective field theory (EFT) approach to incorporate conservative and dissipative radiation-reaction effects in a unified framework. This is achieved by implementing the Schwinger-Keldysh “in-in” formalism and separating conservative and non-conservative terms according to the formulation in [1], which we show promotes Feynman’s i0-prescription and cutting rules to a prominent role at the classical level. The resulting integrals, involving both Feynman and retarded propagators, can be bootstrapped to all orders in the velocity via differential equations with boundary conditions including potential and radiation modes. As a paradigmatic example we provide an ab initio derivation of the classical solution to the scattering problem in general relativity to mathcal{O} (G3). For the sake of completeness, we also reproduce the leading order radiation-reaction effects in classical electrodynamics.

Partition functions and fibering operators on the Coulomb branch of 5d SCFTs

We study 5d mathcal{N} = 1 supersymmetric field theories on closed five-manifolds mathcal{M} 5 which are principal circle bundles over simply-connected Kähler four-manifolds, mathcal{M} 4, equipped with the Donaldson-Witten twist. We propose a new approach to compute the supersymmetric partition function on mathcal{M} 5 through the insertion of a fibering operator, which introduces a non-trivial fibration over mathcal{M} 4, in the 4d topologically twisted field theory. We determine the so-called Coulomb branch partition function on any such mathcal{M} 5, which is conjectured to be the holomorphic ‘integrand’ of the full partition function. We precisely match the low-energy effective field theory approach to explicit one-loop computations, and we discuss the effect of non-perturbative 5d BPS particles in this context. When mathcal{M} 4 is toric, we also reconstruct our Coulomb branch partition function by appropriately gluing Nekrasov partition functions. As a by-product of our analysis, we provide strong new evidence for the validity of the Lockhart-Vafa formula for the five-sphere partition function.

Effective field theory of magnetogenesis identify necessary and sufficient conditions

At astrophysical and cosmological scales, there is a detectable amount of magnetic field. There are several probable origins for this observed magnetic field, including the possibility of its origin in the early Universe. There are several models for primordial magnetogenesis, and if the inflationary background is taken into account, broken conformal invariance is required to generate a sufficient amount of magnetic field. The breaking of conformal invariance is introduced either by new couplings between electromagnetic field and inflaton field or including higher derivative terms to the theory. As a step to unify these different approaches in the literature, we propose an Effective Field Theory (EFT) approach based on expansion about the Hubble parameter (H) and its derivatives, where EFT parameters describe the magnetogenesis scenario in the early Universe, and different choices of parameters correspond to different models.We explicitly show that the generation of primordial magnetic fields requires two necessary conditions — conformal invariance breaking and causal propagation. While broken conformal invariance is a common requirement for primordial magnetogenesis, for the first time, we show that causal propagation is also a necessary condition. We confirm this by considering a specific model of primordial magnetogenesis.

Beyond quantum chaos in emergent dual holography

Black holes are well known to be fast scramblers, responsible for physics of quantum chaos in dual holography. Recently, the Euclidean wormhole has been proposed to play a central role in the chaotic behavior of the spectral form factor. Furthermore, this phenomena was reinterpreted based on an effective field theory approach for quantum chaos. Since the graded nonlinear $\ensuremath{\sigma}$-model approach can describe not only the Wigner-Dyson level statistics but also its Poisson distribution, it is natural to ask whether the dual holography can touch the Poisson regime beyond the quantum chaos. In this study, we investigate disordered strongly coupled conformal field theories in the large central-charge limit. An idea is to consider a quenched average for metric fluctuations and to take into account the renormalization group flow of the metric-tensor distribution function from the UV to the IR boundary. Here, renormalization effects at a given disorder configuration are described by the conventional dual holography. We uncover that the renormalized distribution function shows a power-law behavior universally, interpreted as an infinite randomness fixed point.

One-loop matching of scotogenic model onto standard model effective field theory up to dimension 7

The scotogenic neutrino seesaw model is a minimal extension of the standard model with three ℤ2-odd right-handed singlet fermions N and one ℤ2-odd Higgs doublet η that can accommodate the tiny neutrino mass and provide a dark matter candidate in a unified picture. Due to lack of experimental signatures for electroweak scale new physics, it is appealing to assume these new particles are well above the electroweak scale and take the effective field theory approach to study their effects on low energy observables. In this work we apply the recently developed functional matching formalism to the one-loop matching of the model onto the standard model effective field theory up to dimension seven for the case when all new states N and η are heavy to be integrated out. This is a realistic example which has no tree-level matching due to the ℤ2 symmetry. Using the matching results, we analyze their phenomenological implications for several physical processes, including the lepton number violating effect, the CDF W mass excess, and the lepton flavor violating decays like μ → eγ and μ → 3e.

Effects of three-body forces on the [formula omitted]He–[formula omitted] radiative capture process

The 3He(α,γ)7Be radiative capture reaction has studied using the pionless Effective Field Theory (EFT) approach to determine the cross-section, astrophysical S-factor, and reaction rate in astrophysical energies. We have applied the Faddeev equation method, while taking three-body forces into account. The scattering amplitude in the E1 and E2 transitions to the 7Be ground state (lf=1,Jf=3/2), has computed at Leading Order (LO) considering the Coulomb effects. The thermonuclear reaction results have normalized using NACRE 1999 experimental data. All results are compared with certain theoretical and experimental data and there is good agreement with this data.

Two-photon exchange in (muonic) deuterium at N3LO in pionless effective field theory

We present a study of the two-photon-exchange (2upgamma -exchange) corrections to the S-levels in muonic (mu D) and ordinary (D) deuterium within the pionless effective field theory (EFT). Our calculation proceeds up to next-to-next-to-next-to-leading order (N3LO) in the EFT expansion. The only unknown low-energy constant entering the calculation at this order corresponds to the coupling of a longitudinal photon to the nucleon–nucleon system. To minimise its correlation with the deuteron charge radius, it is extracted using the information about the hydrogen–deuterium isotope shift. We find the elastic 2upgamma -exchange contribution in mu D larger by several standard deviations than obtained in other recent calculations. This discrepancy ameliorates the mismatch between theory and experiment on the size of 2upgamma -exchange effects, and is attributed to the properties of the deuteron elastic charge form factor parametrisation used to evaluate the elastic contribution. We identify a correlation between the deuteron charge and Friar radii, which can help one to judge how well a form factor parametrisation describes the low-virtuality properties of the deuteron. We also evaluate the higher-order 2upgamma -exchange contributions in mu D, generated by the single-nucleon structure and expected to be the most important terms beyond N3LO. The uncertainty of the theoretical result is dominated by the truncation of the EFT series and is quantified using a Bayesian approach. The resulting extractions of the deuteron charge radius from the mu D Lamb shift, the 2S{-}1S transition in D, and the 2S{-}1S hydrogen–deuterium isotope shift, with the respective 2upgamma -exchange effects evaluated in a unified EFT approach, are in perfect agreement.

Light sterile neutrinos, left-right symmetry, and 0νββ decay

We investigate neutrinoless double beta (0νββ) decay rates in minimal left-right symmetric models in presence of relatively light right-handed neutrinos. By use of an effective field theory approach, we systematically include all contributions in the model as well as the dependence of the decay amplitude on the masses of right-handed neutrinos. In type-I and type-II seesaw scenarios, we analyze the impact of right-handed neutrinos heavier than about 10 MeV, showing that this effect can lead to a detection of 0νββ decay in the next-generation experiments even for the normal hierarchy and a relatively large right-handed scale set by the mass of hypothetical right-handed gauge bosons. Finally, we comment on a possible connection between light right-handed neutrinos and the strong CP problem.

Magnetic structure of few-nucleon systems at high momentum transfers in a chiral effective field theory approach

The five low-energy constants (LECs) in the electromagnetic current derived in chiral effective field theory ($\chi$EFT) up to one loop are determined by a simultaneous fit to the $A\,$=$\,2$--3 nuclei magnetic moments and to the deuteron magnetic form factor and threshold electrodisintegration at backward angles over a wide range of momentum transfers. The resulting parametrization then yields predictions for the $^3$He/$^3$H magnetic form factors in excellent accord with the experimental values for momentum transfers ranging up to $\approx 0.8$ GeV/c, beyond the expected regime of validity of the $\chi$EFT approach. The calculations are based on last-generation two-nucleon interactions including high orders in the chiral expansion and derived by Entem, Macheleidt, and Nosyk [Phys.\ Rev.\ C {\bf 96}, 024004 (2017)] and by Piarulli {\it et al.} [Phys.\ Rev.\ C {\bf 94}, 054007 (2016)], using different $\chi$EFT formulations. In the $A\,$=$\,3$ calculations, (chiral) three-nucleon interactions are also accounted for. The model dependence resulting from these different formulations of the interactions is found to be mild for momentum transfer below $\approx0.8$ GeV/c. An analysis of the convergence of the chiral expansion is also provided.

A bridge to new physics: proposing new — and reviving old — explanations of aμ

The 4.2 σ tension in the combined measurement of the anomalous magnetic moment of the muon, aμ, and the Standard Model prediction strongly suggests the existence of beyond the Standard Model physics. Following the Standard Model Effective Field Theory approach, we study a particular topology, the bridge diagram, which gives a chirally enhanced contribution to aμ. We classify all possible 2- and 3-field SM extensions that can generate this contribution and present the full aμ result for them. Within our approach, we find that several 2-field fermion-scalar extensions which had been previously discarded in the literature — when only the Yukawa-suppressed contribution was considered — can actually be viable models to explain the observed anomaly. Furthermore, the 3-field extensions which generate the bridge diagram represent a new class of models to account for aμ. We explore a particular 3-field extension which, beyond explaining aμ, can also account for the neutral B-meson anomalies and the Cabibbo angle anomaly. We present the full one-loop matching for this model and a one-loop phenomenological study.

Dark matter freeze-in with a heavy mediator: beyond the EFT approach

We study dark matter freeze-in scenarios where the mass of the mediator particle that couples dark matter to the Standard Model is larger than the reheat temperature, TRH, in the early Universe. In such setups, the standard approach is to work with an effective field theory (EFT) where the mediator is integrated out. We examine the validity of this approach in various generic s- and t-channel mediator frameworks. We find that the EFT approach breaks down when the mediator mass is between one to two orders of magnitude larger than TRH due to various effects such as s-channel resonance, a small thermally-suppressed abundance of the mediator, or decays of Standard Model particles through loops induced by the mediator. This highlights the necessity of including these contributions in such dark matter freeze-in studies. We also discuss the collider phenomenology of the heavy mediators, which is qualitatively different from standard freeze-in scenarios. We highlight that, due to the low TRH, the Standard Model-dark matter coupling in these scenarios can be relatively larger than in standard freeze-in scenarios, improving the testability prospects of these setups.

Future projections on the anomalous WWγγ couplings in hadron–hadron interactions at the FCC-hh

We carry out a study in the approach of a dimension-eight effective field theory on the anomalous quartic WWγγ couplings that arise from the process pp → Wγγ at the Future Circular Collider-hadron hadron (FCC-hh). The process is sensitive to the WWγγ vertex, and future projections on the anomalous f M,i /Λ4 and f T,j /Λ4 couplings can be put by measurements of Wγγ production. We illustrate the physics opportunities and reach of the FCC-hh operating for a high integrated luminosity scenario of of proton–proton collisions at a center-of-mass energy of TeV and systematic uncertainties of δ sys = 0%, 3%, 5%, 10%. Production cross-sections of the signal and the sensitivity constraints on the anomalous f M,i /Λ4 and f T,j /Λ4 couplings at 95% C.L. are identified through the leptonic and hadronic decay modes of the W-boson. The FCC-hh sensitivity on these anomalous couplings is expected might reach up to the order of magnitude . These sensitivity perspectives indicate that the pp → Wγγ channel at the FCC-hh has a greater potential to search for the anomalous quartic WWγγ couplings and to search for new physics than present colliders.