Haut PDF The effective field theory of K-mouflage

The effective field theory of K-mouflage

The effective field theory of K-mouflage

theories where the cosmological behaviour is decoupled from the small-scale behaviour 2 . The dark energy effective action for models like K-mouflage does not carry new infor- mation which cannot be extracted from the original non-linear Lagrangian. In that respect, the purpose of our paper is twofold. First we show that the complete K-mouflage theory can be defined not only by its Lagrangian but also by two functions of the cosmological scale factor. Given these two functions, it is straightforward to reconstruct the original La- grangian, to derive the cosmological background evolution and to deduce the effective dark energy effective theory at any order. This reconstruction can be easily used at second order in the effective theory, which is enough to analyse all the linear observables of the models and eventually to compare them with data. Secondly, the reconstruction mapping does not require any knowledge of the initial conditions in the early Universe and only requires the
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The effective field theory of multi-component fluids

The effective field theory of multi-component fluids

many models (for example of the late time universe) the equations of scalar (or even vector) fields can also be written using fluid variables such as density, pressure and anisotropic stress. This adds up to the need for a general framework to classify and describe fluid interactions in cosmological perturbation theory. To simplify the process of model testing, a useful strategy is to search in the data for specific features shared by classes of models. In this work we develop a framework, exclusively based on symmetry arguments, that describes th e dynamics of cosmological perturbations at large scales in multi-component fluids. We use the Effective Field Theory (EFT) of Fluids [20–22] to describe the propagation of gapless sound waves, i.e phonons, in continuous media at low energies (or equivalently large distances). The power of the effective field theory is that given the low-energy degrees of freedom and the symmetries that characterize them, the form of the action is completely determined, with strong relations between its various terms. This framework is then able to capture at once several microscopic models that share the same degrees of freedom and symmetry at large distances.
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Dark Energy and Modified Gravity in the Effective Field Theory of Large-Scale Structure

Dark Energy and Modified Gravity in the Effective Field Theory of Large-Scale Structure

Abstract We develop an approach to compute observables beyond the linear regime of dark matter perturbations for general dark energy and modified gravity models. We do so by combining the Effective Field Theory of Dark Energy and Effective Field Theory of Large-Scale Structure approaches. In particular, we parametrize the linear and nonlinear effects of dark energy on dark matter clustering in terms of the Lagrangian terms introduced in a companion paper [ 1 ], focusing on Horndeski theories and assuming the quasi-static approximation. The Euler equation for dark matter is sourced, via the Newtonian potential, by new nonlinear vertices due to modified gravity and, as in the pure dark matter case, by the effects of short-scale physics in the form of the divergence of an effective stress tensor. The effective fluid introduces a counterterm in the solution to the matter continuity and Euler equations, which allows a controlled expansion of clustering statistics on mildly nonlinear scales. We use this setup to compute the one-loop dark-matter power spectrum.
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The "Folk Theorem" on Effective Field Theory: How Does It Fare in Nuclear Physics?

The "Folk Theorem" on Effective Field Theory: How Does It Fare in Nuclear Physics?

That chiral symmetry could play an important role in nuclear physics was recognized already in early 1970’s. It was implicit in considerations of pion-mediated nuclear potentials, but the first realization of its potential impact in nuclear physics was in nuclear response functions to the electroweak external potential. There was no effective field theory then but just phenomenological Lagrangians built with identified hadronic degrees of freedom considered to be relevant to the kinematic regime concerned. Both the nuclear potentials and response functions were then calculated only – and by necessity – at the tree order. It was in calculating the EW response functions that the soft-pion theorems, applicable at the tree order with the Lagrangian, were applied to pionic exchange currents. Given that the pion-exchange represented dominant contribution, with heavier meson degrees of freedom suppressed by their heavy mass, the soft-pion contribution with constraints from the current algebras were calculated reliably parameter-free. This represented the first indication that chiral symmetry could figure significantly in nuclear processes [21]. The further development in this line of reasoning led to the prediction that the M 1 matrix element and the weak axial- charge matrix element should receive an important contribution from the soft-pion theorems. It was recognized on the ground of the soft-pion theorems that the axial-charge transitions can have an extremely clean meson-exchange effects [22]. Indeed the nuclear EFT so formulated led to high precision calculations of electroweak processes in light nuclei, a brief summary of which is given in [23].
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Comments on the diphoton excess: critical reappraisal of effective field theory interpretations

Comments on the diphoton excess: critical reappraisal of effective field theory interpretations

In this paper, we showed that the effective field theory of the new state S, combined with the standard model, leads to non-trivial signatures at the level of the LHC observables. In section 4 , we concentrated on the decay of S and showed that there are necessarily decays into other electroweak final states, with non-trivial relations between the branching ratios among the final states. Importantly, the branching-ratio relations and sum rules we derived in that section will be tested in future runs of the collider. In section 5 we asked a related question: given the effective field theory and the rate to diphotons observed so far, how can observables, such as ratios of rates that survive VBF cuts to inclusive rates, tell us about the coupling of S to non-electroweak states, such as quarks. We showed that the VBF ratio is a discriminator between gluon-fusion production and, for example, quark anti-quark produc- tion. This is particularly relevant, given that in section 2 we showed that current LHC data supports production through either gluon fusion or heavy quark annihilation. Similarly, in section 6 we showed that additional constraints on the coupling of the resonance to non- electroweak states are found when considering simultaneously the total width along with the VBF ratio. In summary, we have provided a variety of simple relations directly among observables at the LHC which, in light of the low energy effective field theory, may have profound implications for understanding the nature of the excess as more data accumulates.
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The Quantum Field Theory of K-mouflage

The Quantum Field Theory of K-mouflage

F-91191 Gif-sur-Yvette, C´ edex, France (Dated: February 8, 2017) We consider K-mouflage models, which are K-essence theories coupled to matter. We analyze their quantum properties and in particular the quantum corrections to the classical Lagrangian. We setup the renormalization program for these models and show that, contrary to renormalizable field theories where renormalization by infinite counterterms can be performed in one step, K-mouflage theories involve a recursive construction whereby each set of counterterms introduces new divergent quantum contributions which in turn must be subtracted by new counterterms. This tower of counterterms can be in principle constructed step by step by recursion and allows one to calculate the finite renormalized action of the model. In particular, it can be checked that the classical action is not renormalized and that the finite corrections to the renormalized action contain only higher-derivative operators. We concentrate then on the regime where calculability is ensured, i.e., when the corrections to the classical action are negligible. We establish an operational criterion for classicality and show that this is satisfied in cosmological and astrophysical situations for (healthy) K-mouflage models which pass the Solar System tests. These results rely on perturbation theory around a background and are only valid when the background configuration is quantum stable. We analyze the quantum stability of astrophysical and cosmological backgrounds and find that models that pass the Solar System tests are quantum stable. We then consider the possible embedding of the K-mouflage models in an Ultra-Violet completion. We find that the healthy models which pass the Solar System tests all violate the positivity constraint which would follow from the unitarity of the putative UV completion, implying that these healthy K-mouflage theories have no UV completion. We then analyze their behavior at high energy, and we find that the classicality criterion is satisfied in the vicinity of a high-energy collision, implying that the classical K-mouflage theory can be applied in this context. Moreover, the classical description becomes more accurate as the energy increases, in a way compatible with the classicalization concept.
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The role of scalar mesons in extended perturbation scheme for effective field theory

The role of scalar mesons in extended perturbation scheme for effective field theory

∗ Institut für Theoretische Physik II, Ruhr-Universität Bochum, Bochum, Germany † Department of Physics and Technology, University of Bergen, Bergen, Norway ∗∗ Department of High Energy Physics, Saint-Petersburg State University, Saint-Petersburg, Russia Abstract. We argue how it is possible to apply the general scheme of the effective scattering theory (EST) to the description of the hadronic processes. The results of the numerical tests of sum rules for πN spectrum parameters that follow from the bootstrap system allow us to claim the consistency
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Dark matter effective field theory scattering in direct detection experiments

Dark matter effective field theory scattering in direct detection experiments

i and c τ 0 j and depend on properties such as target element, WIMP mass, WIMP spin, WIMP velocity, and nuclear recoil energy. We evaluate the A ττ ij 0 without integrating over the dark matter velocity distribution to avoid introducing more variables. Amplitudes are summed over the isotopes for a given element according to their natural abundances. Finding the eigenvectors of this matrix will give the “principal components" of the interaction space. We expect that three of the four eigenvalues should be small, since the matrix for a single isotope is an outer product and therefore should have a single nonzero eigenvalue. The vector with the largest eigenvalue corresponds to the maximal ampli- tude for scattering in the interference space under consid- eration, while the three small eigenvalues correspond to local extrema in the scattering amplitude which tend to suppress the event rate. To be maximally sensitive to the parameter space for a given interference case, we would like to choose target elements whose constructive interfer- ence eigenvectors span the space of interactions.
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Mean-field theory of inhomogeneous fluids

Mean-field theory of inhomogeneous fluids

In a seminal pair of papers from 1967, Barker and Henderson combined the approach of Zwanzig with the Percus-Yevick results for hard spheres to obtain the first true microscopic theory of liquids, embedding the ideas of van der Waals within the framework of statistical mechanics [ 10 , 11 ] (reviewed in [ 12 ]). In addition to providing a correct pertur- bative treatment of interparticle attractions, they also devised the first prescription for mapping a softly repulsive refer- ence system (required to treat, e.g., Lennard-Jones particles) onto a system of hard spheres with an effective, temperature- dependent diameter. The theory worked very well for a variety of model systems, accurately reproducing data for the thermodynamics and structure obtained from Monte Carlo simulation. Although there nowadays exist more elaborate ap- proaches to the thermodynamics, namely, the self-consistent Ornstein-Zernike approximation of Høye and Stell [ 13 , 14 ] and the heirarchical reference theory of Reatto and Parola [ 15 ], these “beyond mean-field” approximations are not easy to implement and only yield significant differences from the Barker-Henderson theory in the vicinity of the critical point.
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Effective field theory for gravitational radiation in scalar-tensor gravity

Effective field theory for gravitational radiation in scalar-tensor gravity

We now discuss why we restrict to this action and some ways to extend it. 1.1 The gravitational action While trying to extend the NRGR formalism to dark energy/scalar field models we im- mediately encounter an obstruction. It is well known that, to pass Solar System tests, modified gravity theories display screening mechanisms that make the scalar interac- tions weaker in high density environments. For instance, most theories belonging to the Galileon/Horndeski [ 37 – 39 ] and “beyond Horndeski” [ 40 – 44 ] classes have a rich structure of non-linear terms in their Lagrangians that become more important close to the sources, thereby screening the effects of the scalar fluctuations [ 45 , 46 ]. While it is legitimate to neglect such non-linearities on the largest cosmological scales, they are expected to play a major role in the vicinity of the binaries, causing a breakdown of the perturbative expan- sion that we use in this paper.
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Characterizing hydrodynamical fluctuations in heavy-ion collisions from effective field theory approach

Characterizing hydrodynamical fluctuations in heavy-ion collisions from effective field theory approach

1. Introduction Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory provides a testing ground for QCD. Collisions of heavy ions at relativistic speed create quark gluon plasma (QGP) which is the high temperature, high density phase of the QCD phase diagram. QGP behaves in a surprising way in which its evolution can be modelled as a nearly ideal fluid [1]. Therefore, hydrodynamics provides a useful framework to study the collective motion and its fluctuations of QGP. One of the simplest models is the Bjorken flow [2]. The Bjorken flow describes a static fluid in a Boost invariant background which agrees well with experimental measurements.
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Field theory on the light-front

Field theory on the light-front

intermediate state without the need to include them explicitly, provided the effective Lagrangian has the right dynamics to generate these resonances. 5. Perspectives The general framework we presented above to study the structure of relativistic compound systems in light-front dynamics in a nonperturbative way relies on three main advances: i) the con- struction of a covariant formulation of light-front dynamics [ 2 , 3 ] in order to control any violation of rotational invariance; ii) the development of an appropriate renormalization scheme — the so- called Fock sector dependent renormalization scheme — to deal with the truncation of the Fock expansion [ 4 ]; iii) the use of an appropriate regularization scheme — the so-called Taylor-Lagrange regularization scheme — very well adapted to systematic calculations in light-front dynamics [ 11 ]. These advances should enable us to have a predictive framework order by order in the Fock expansion. We shall complete in the future this description by considering physical systems involv- ing spontaneous symmetry breaking. It is known that these systems can be described in light-front dynamics by the consideration of zero-mode contributions, in the λ φ 4 theory in 1 + 1 dimension for instance [ 15 ]. Their full calculation in 3 + 1 dimensions within the general framework presented above remains to be done.
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Effective Theory of Non-Adiabatic Quantum Evolution Based on the Quantum Geometric Tensor

Effective Theory of Non-Adiabatic Quantum Evolution Based on the Quantum Geometric Tensor

bands [6]. Their approach allowed to confirm the anoma- lous Hall effect predicted by Karplus and Luttinger [5] and to express this effect in terms of Berry curvature. Following this approach, we derive our corrected equa- tions up to the second order in external constant force for a two-band system using perturbation theory. We con- sider the case of geodesic trajectory of the wavepacket, corresponding to the evolution of the effective field on the equator of the Bloch sphere. We show that in this configuration, all first-order and most of the second-order corrections to the semiclassical equations of motion are zero, except the particular correction due to the differ- ence of the metric on the equator and at the equilibrium deviation angle of the spin.
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Effective theory of self-interacting dark matter

Effective theory of self-interacting dark matter

3.1 Wilsonian treatment of divergences Potentials that go to infinity faster than 1/r 2 at the origin are called singular [36] and generically arise in dark sectors with spinning dm and/or with some strong dynamics. The occurrence of unphysical behavior originating from the infinitely large energies of such potentials are analogous to the infinities of quantum field theory (qft). These inconsistencies arise when one extrapolates a long-range potential to arbitrarily short distances where ultraviolet physics should be taken into account. In fact, the Schr¨odinger equation can be renormalized by adopting the Wilsonian renormalization group (rg) methods of qft [37]: the singular potential is regulated at a short distance a and augmented with a series of local operators that parametrize the unknown uv physics,
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Effective Theory of Magnetization Plateaux in the Shastry-Sutherland Lattice

Effective Theory of Magnetization Plateaux in the Shastry-Sutherland Lattice

In all these effective models approaches, one must dis- tinguish the two steps: first, an effective Hamiltonian is derived; then, because it is still an interacting quantum problem, one needs to resort to an efficient technique to study it. Although it is a bosonic model, the presence of positive off-diagonal terms prohibits quantum Monte Carlo calculations. Possible alternatives are mean-field analysis [ 12 ] which main drawback is to overestimate the tendency to form plateaux and also needs a careful numerical analy- sis on finite clusters. Given the various small amplitudes, we prefer not to make any further assumption, and we provide exact diagonalizations (ED) of these effective models on finite lattices.
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Philosophical foundations of effective field theories

Philosophical foundations of effective field theories

Simply put, scientific realism is the stance that takes our best sci- entific theories to offer approximately true descriptions of the world. The history of science shows, however, that many past theories have proven to make radically false claims about unobservable entities and structures when these theories are assessed relative to their succes- sors. This suggests that our current best theories might be in the same situation. The most popular response to this problem is a po- sition called ‘selective realism’: even though our best theories do not get everything right, they still contain parts that are likely to remain (approximately) true [30, 36, 50]. Williams [48] and J. Fraser [19] have recently defended this position in the context of QFT: they argue that Wilsonian RG methods provide ‘local’ (i.e., restricted to QFT) tools to distinguish essential parts in current EFTs that are likely to with- stand future theory change and give (approximately) true descriptions of the world. In particular, RG methods give selective realists some confidence in the claim that the low-energy content of the presently most successful EFTs is largely independent of the high-energy con- tent of future theories and is therefore likely to remain unaffected by the discovery of new high-energy physics.
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Renormalizability of Liouville quantum field theory at the Seiberg bound

Renormalizability of Liouville quantum field theory at the Seiberg bound

(|∂ z f | 2 + g(z)|f| 2 )dz. These norms are equivalent for all continuous conformal metrics and we denote the space simply by H 1 ( ˆ C ). Finally we define H −1 ( ˆ C ) as the dual space and denote the dual pairing by hX, fi. The LQFT measure will be defined as a measure on H −1 ( ˆ C ). It will be constructed using the Gaussian Free Field (GFF) on ˆ C . As is well known the GFF in such a setup is only defined modulo a constant. For LQFT it is important to include this constant as an integration variable. In general the GFF is a Gaussian random field whose covariance is the Green function of the Laplace operator. In our setup the Laplace operator is given by ∆ g = 4g(z) −1 ∂ ¯ z ∂ z . Some care is needed here since ∆ g is not invertible. Indeed, −∆ g is a non-negative self-
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Nonlinear Effective Theory of Dark Energy

Nonlinear Effective Theory of Dark Energy

Initially implemented for inflation in [ 4 , 5 ], a convenient way to describe dark energy and modified gravity models characterized by a single scalar degree of freedom and to connect them to observational predictions in terms of a minimal number of parameters is the Effective Field Theory of Dark Energy (EFTofDE) [ 6 – 10 ] (see [ 11 – 13 ] for reviews); see also [ 14 – 17 ] for analogous approaches in dark energy. In the EFTofDE approach, one assumes that the time-diffeomorphism invariance of the gravitational sector is broken by the dark-energy field. In the so-called unitary gauge, the gravitational action can be constructed as the sum of all possible operators in terms of the metric, invariant under time-dependent spatial diffeomorphisms and ordered in the number of perturbations and derivatives. Physical principles such as locality, causality, stability, and unitarity can be imposed at the level of the Lagrangian, so that the predicted signatures are physically acceptable.
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K-mouflage Cosmology: Formation of Large-Scale Structures

K-mouflage Cosmology: Formation of Large-Scale Structures

the one of Λ-CDM. At the perturbative level, and first in the linear theories, deviations from GR occur on scales lower than the Compton wavelength of the scalar field [29]. As Solar System tests and the screening of the Milky Way imply that the cosmological range of the scalar must be less than 1 Mpc [30], the effects of these models on linear scales are suppressed and only in the quasilinear to mildly nonlinear regimes one can expect to see signif- icant deviations. Symmetrons and dilatons screen grav- ity in a stronger way in the local environment imply- ing that constraints on these models are less severe than on chameleon-f (R) theories. This implies that the ef- fects of the symmetron and to a lesser extent of the dila- ton on large-scale structures are enhanced compared to chameleon-f (R) models. Typically, one expects to see a peak in the deviations from GR on the scales correspond- ing to the range of the scalar field, especially in the power spectrum of density fluctuations [9]. On small and large scales, the models converge towards GR. On small scales, this is due to the screening effect and on large scales this is also the screening property outside the Compton ra- dius.
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Effective field theory of post-newtonian gravity including spins

Effective field theory of post-newtonian gravity including spins

Institut de Physique Th´ eorique, CEA Saclay, Universit´ e Paris-Saclay, 91191 Gif-sur-Yvette, France We present in detail an Effective Field Theory (EFT) formulation for the essential case of spinning objects as the components of inspiralling compact binaries. We review its implemen- tation, carried out in a series of works in recent years, which leveled the high post-Newtonian (PN) accuracy in the spinning sector to that, recently attained in the non-spinning sector. We note a public package, “EFTofPNG”, that we recently created for high precision computation in the EFT of PN Gravity, which covers all sectors, and includes an observables pipeline.
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