Renormalization Group Scaling Research Articles

Scalar-Tensor gravity with system-dependent potential and its relation with Renormalization Group extended General Relativity

We show that Renormalization Group extensions of the Einstein-Hilbert action for large scale physics are not, in general, a particular case of standard Scalar-Tensor (ST) gravity. We present a new class of ST actions, in which the potential is not necessarily fixed at the action level, and show that this extended ST theory formally contains the Renormalization Group case. We also propose here a Renormalization Group scale setting identification that is explicitly covariant and valid for arbitrary relativistic fluids.

Background independent exact renormalization group for conformally reduced gravity

Within the conformally reduced gravity model, where the metric is parametrised by a function $f(\phi)$ of the conformal factor $\phi$, we keep dependence on both the background and fluctuation fields, to local potential approximation and $\mathcal{O}(\partial^2)$ respectively, making no other approximation. Explicit appearances of the background metric are then dictated by realising a remnant diffeomorphism invariance. The standard non-perturbative Renormalization Group (RG) scale $k$ is inherently background dependent, which we show in general forbids the existence of RG fixed points with respect to $k$. By utilising transformations that follow from combining the flow equations with the modified split Ward identity, we uncover a unique background independent notion of RG scale, $\hat k$. The corresponding RG flow equations are then not only explicitly background independent along the entire RG flow but also explicitly independent of the form of $f$. In general $f(\phi)$ is forced to be scale dependent and needs to be renormalised, but if this is avoided then $k$-fixed points are allowed and furthermore they coincide with $\hat k$-fixed points.

Finding critical points using improved scaling Ansätze

Analyzing in detail the first corrections to the scaling hypothesis, we develop accelerated methods for the determination of critical points from finite size data. The output of these procedures is sequences of pseudo-critical points which rapidly converge towards the true critical points. The convergence is faster than that obtained with the fastest method available to date, which consists of estimating the location of the gap's closure (the so called phenomenological renormalization group). Having fast converging sequences at our disposal allows us to draw conclusions on the basis of shorter system sizes. This can be extremely important in particularly hard cases such as two-dimensional quantum systems with frustrations, or in Monte Carlo simulations when the sign problem occurs. After reviewing the most efficient techniques available to date, we test the effectiveness of the proposed methods both analytically on the basis of the one-dimensional XY model and numerically at phase transitions occurring in non-integrable spin models. In particular, we show how a new Homogeneity Condition Method is able to produce fast converging sequences in correspondence to the Berezinskii–Kosterlitz–Thouless (BKT) transition simply by making use of ground-state quantities on relatively small systems. Remarkably, our method tested on the frustrated spin-1/2 Heisenberg model gives a BKT critical point which is incompatible with the ones present in the past literature based on different methods. This discrepancy raises the fundamental question of determining the correct renormalization group approach and scaling assumptions that yield to the sequences converging to the true critical point. Finally, we formulate a general prescription that allows us to analyze and efficiently locate critical points in a variety of cases, without knowing in advance the universality class of the tested transition. Even if our methods are tested here in one dimension, we expect them to be valid in any spatial dimensionality and both for quantum and classical statistical systems.

Topological entropy and renormalization group flow in 3-dimensional spherical spaces

We analyze the renormalization group (RG) flow of the temperature independent term of the entropy in the high temperature limit \beta/a<<1 of a massive field theory in 3-dimensional spherical spaces M_3 with constant curvature 6/a^2. For masses lower than 2\pi/\beta, this term can be identified with the free energy of the same theory on M_3 considered as a 3-dimensional Euclidean space-time. The non-extensive part of this free energy, S_hol, is generated by the holonomy of the spatial metric connection. We show that for homogeneous spherical spaces the holonomy entropy S_hol decreases monotonically when the RG scale flows to the infrared. At the conformal fixed points the values of the holonomy entropy do coincide with the genuine topological entropies recently introduced. The monotonic behavior of the RG flow leads to an inequality between the topological entropies of the conformal field theories connected by such flow, i.e. S_top^UV > S_top^IR. From a 3-dimensional viewpoint the same term arises in the 3-dimensional Euclidean effective action and has the same monotonic behavior under the RG group flow. We conjecture that such monotonic behavior is generic, which would give rise to a 3-dimensional generalization of the c-theorem, along the lines of the 2-dimensional c-theorem and the 4-dimensional a-theorem. The conjecture is related to recent formulations of the F-theorem. In particular, the holonomy entropy on lens spaces is directly related to the topological R\'enyi entanglement entropy on disks of 2-dimensional flat spaces.

Amplitude modulation for the Swift-Hohenberg and Kuramoto-Sivashinski equations

Employing a harmonic balance technique inspired from the methods of Renormalization Group and Multiple Scales [R. E. O’Malley, Jr. and E. Kirkinis. “A combined renormalization group-multiple scale method for singularly perturbed problems,” Stud. Appl. Math. 124(4), 383–410, (2010)], we derive the amplitude equations for the Swift-Hohenberg and Kuramoto-Sivashinski equations to arbitrary order in the context of roll patterns. This new and straightforward derivation improves previous attempts and can be carried-out with symbolic computation that minimizes effort and avoids error.

Guises and disguises of quadratic divergences

In this contribution, we present a new perspective on the control of quadratic divergences in quantum field theory, in general, and in the Higgs naturalness problem, in particular. Our discussion is essentially based on an approach where UV divergences are parameterized, after being reduced to basic divergent integrals (BDI) in one internal momentum, as functions of a cutoff and a renormalization group scale λ. We illustrate our proposal with well-known examples, such as the gluon vacuum self energy of QCD and the Higgs decay in two photons within this approach. We also discuss frameworks in effective low-energy QCD models, where quadratic divergences are indeed fundamental.

Calculation of size for bound-state constituents

Elements are given of a calculation that identifies the size of a proton in the Schroedinger equation for lepton-proton bound states, using the renormalization group procedure for effective particles (RGPEP) in quantum field theory, executed only up to the second order of expansion in powers of the coupling constant. Already in this crude approximation, the extraction of size of a proton from bound-state observables is found to depend on the lepton mass, so that the smaller the lepton mass the larger the proton size extracted from the same observable bound-state energy splitting. In comparison of Hydrogen and muon-proton bound-state dynamics, the crude calculation suggests that the difference between extracted proton sizes in these two cases can be a few percent. Such values would match the order of magnitude of currently discussed proton-size differences in leptonic atoms. Calculations using the RGPEP of higher order than second are required for a precise interpretation of the energy splittings in terms of the proton size in the Schroedinger equation. Such calculations should resolve the conceptual discrepancy between two conditions: that the renormalization group scale required for high accuracy calculations based on the Schroedinger equation is much smaller than the proton mass (on the order of a root of the product of reduced and average masses of constituents) and that the energy splittings due to the physical proton size can be interpreted ignoring corrections due to the effective nature of constituents in the Schr\"odinger equation.

Renormalization of anticrossings in interacting quantum wires with Rashba and Dresselhaus spin-orbit couplings

We discuss how electron-electron interactions renormalize the spin-orbit induced anticrossings between different subbands in ballistic quantum wires. Depending on the ratio of spin-orbit coupling and subband spacing, electron-electron interactions can either increase or decrease anticrossing gaps. When the anticrossings are closing due to a special combination of Rashba and Dresselhaus spin-orbit couplings, their gap approaches zero as an interaction dependent power law of the spin-orbit couplings, which is a consequence of Luttinger liquid physics. Monitoring the closing of the anticrossings allows to directly measure the related renormalization group scaling dimension in an experiment. If a magnetic field is applied parallel to the spin-orbit coupling direction, the anticrossings experience different renormalizations. Since this difference is entirely rooted in electron-electron interactions, unequally large anticrossings also serve as a direct signature of Luttinger liquid physics. Electron-electron interactions furthermore increase the sensitivity of conductance measurements to the presence of anticrossing.

Revisiting the vacuum energy scenario from the renormalization group method of the QFT theory

In this paper the vacuum energy scenario (or time-dependent cosmological constant) from the renormalization group (RG) equation is studied. By considering the renormalization group scale described by the Hubble parameter, we apply the current observational data to constrain this RG dark energy model. Concretely, the different combinations of cosmic observational data, including the kinematical and the dynamical part, are investigated to constrain the RG model. For comparison we also consider the cosmic constraints on the dark model by taking the Ricci scalar as the renormalization group scale. In addition, we compare these two RG dark energy models with the cosmological constant.

Renormalization group scaling of Higgs operators and h → γγ decay

Abstract We compute the renormalization of dimension six Higgs-gauge boson operators that can modify the h → γγ rate at tree-level. Operator mixing is shown to lead to an important modification of new physics effects which has been neglected in past calculations. We also find that the usual formula for the S oblique parameter contribution of these Higgs-gauge boson operators needs additional terms to be consistent with renormalization group evolution. We study the implications of our results for Higgs phenomenology and for new physics models which attempt to explain a deviation in the h → γγ rate. We derive a new relation between the S parameter and the h → γγ and h → Zγ decay rates.

Renormalization group scale-setting from the action—a road to modified gravity theories

The renormalization group (RG) corrected gravitational action in Einstein–Hilbert and other truncations is considered. The running scale of the RG is treated as a scalar field at the level of the action and determined in a scale-setting procedure recently introduced by Koch and Ramirez for the Einstein–Hilbert truncation. The scale-setting procedure is elaborated for other truncations of the gravitational action and applied to several phenomenologically interesting cases. It is shown how the logarithmic dependence of the Newton's coupling on the RG scale leads to exponentially suppressed effective cosmological constant and how the scale-setting in particular RG-corrected gravitational theories yields the effective f(R) modified gravity theories with negative powers of the Ricci scalar R. The scale-setting at the level of the action at the non-Gaussian fixed point in Einstein–Hilbert and more general truncations is shown to lead to universal effective action quadratic in the Ricci tensor.

Yukawa unification and the superpartner mass scale

Naturalness in supersymmetry (SUSY) is under siege by increasingly stringent LHC constraints, but natural electroweak symmetry breaking still remains the most powerful motivation for superpartner masses within experimental reach. If naturalness is the wrong criterion then what determines the mass scale of the superpartners? We motivate supersymmetry by (1) gauge coupling unification, (2) dark matter, and (3) precision b-tau Yukawa unification. We show that for an LSP that is a bino-Higgsino admixture, these three requirements lead to an upper-bound on the stop and sbottom masses in the several TeV regime because the threshold correction to the bottom mass at the superpartner scale is required to have a particular size. For tan beta about 50, which is needed for t-b-tau unification, the stops must be lighter than 2.8 TeV when A_t has the opposite sign of the gluino mass, as is favored by renormalization group scaling. For lower values of tan beta, the top and bottom squarks must be even lighter. Yukawa unification plus dark matter implies that superpartners are likely in reach of the LHC, after the upgrade to 14 (or 13) TeV, independent of any considerations of naturalness. We present a model-independent, bottom-up analysis of the SUSY parameter space that is simultaneously consistent with Yukawa unification and the hint for m_h = 125 GeV. We study the flavor and dark matter phenomenology that accompanies this Yukawa unification. A large portion of the parameter space predicts that the branching fraction for B_s to mu^+ mu^- will be observed to be significantly lower than the SM value.

Spectra of a MHD plasma forced by power-law noise

Scalings of a noise-driven two-dimensional homogeneous MHD plasma are considered by using numerical simulations. The noise is a Gaussian random process whose two-point correlation function is delta-correlated in time while obeying a power-law spectrum k2−2δ that determines the input rate of the energy where k is the inverse of the scale length. For the case of infrared forcing, δ > 2, the scaling of the energy spectrum is found to closely follow the phenomenological prediction of k−3/2. In the other case of ultraviolet forcing where δ < 2, the renormalization-group scale, which is k1−4δ/3, is found to approximately hold for the energy spectrum.

Scalings of forced Hasegawa–Mima equation by power-law noise

For the plasma modeled by the Hasegawa–Mima equation forced by a noise, Kolmogorov-type phenomenology (KP) predicts the power-law scaling in two inertial regimes. In the spatial scale, which is larger than the ion gyroradius, the energy spectrum scales as k−11/3 where the energy cascades to larger scales and k−5 where the enstrophy is transferred to smaller scales down to the dissipation range. The renormalization-group (RG) approach, however, provides different scaling k−1−4δ/3 that strongly depends on the power exponent δ of the noise spectrum. Through numerical simulations it is found that, for δ ⩽ 2 or δ ⩾ 3, the energy spectrum follows KP while, for 2 ⩽ δ ⩽ 3, RG scaling prevails.

Asymptotically safe phantom cosmology

We consider quantum modifications to phantom cosmology in a Friedmann-Robertson-Walker spacetime. The cosmological evolution equations improved by the renormalization group are obtained. For exponential potential, we find two types of cosmological fixed point; the renormalization group scale either freezes in, or continues to evolve with scale factor. We discuss the implications of each of these points, and investigate especially whether the big rip can be avoided. If the fixed point of renormalization group flow coincides with the cosmological fixed point, the universe will be dominated by dark matter and will be free from the big rip.

Equilibrium and off-equilibrium trap-size scaling in one-dimensional ultracold bosonic gases

We study some aspects of equilibrium and off equilibrium quantum dynamics of dilute bosonic gases in the presence of a trapping potential. We consider systems with a fixed number of particles N and study their scaling behavior with increasing the trap size. We focus on one-dimensional (1D) bosonic systems, such as gases described by the Lieb-Liniger model and its Tonks-Girardeau limit of impenetrable bosons, and gases constrained in optical lattices as described by the Bose-Hubbard model. We study their quantum (zero-temperature) behavior at equilibrium and off equilibrium during the unitary time evolution arising from changes of the trapping potential, which may be instantaneous or described by a power-law time dependence, starting from the equilibrium ground state for a initial trap size. Renormalization-group scaling arguments, analytical and numerical calculations show that the trap-size dependence of the equilibrium and off-equilibrium dynamics can be cast in the form of a trap-size scaling in the low-density regime, characterized by universal power laws of the trap size, in dilute gases with repulsive contact interactions and lattice systems described by the Bose-Hubbard model. The scaling functions corresponding to several physically interesting observables are computed. Our results are of experimental relevance for systems of cold atomic gases trapped by tunable confining potentials.

Incommensurate charge correlation and phase diagram of the one-dimensional superlatticeHubbard model at half-filling

We study the phase diagram of a half-filled one-dimensionalsuperlattice Hubbard model with an alternating orbital energy ± ϵ/2 and on-siteCoulomb repulsion UA and UB using the density-matrix renormalization group and finite-size scaling analysis. For, we observe an incommensurate charge correlation phase. ForUB = 0, wefind a transition from the band insulating phase to the correlated metallic phase at the critical pointϵ = UA/2. ForUB > 0, we find three insulating phases as in the ionic Hubbard model. In the gapless region, thecorrelation functions exhibit the asymptotic behavior of power-law decay as in theTomonaga–Luttinger liquid.

Galaxy rotation curves from general relativity with renormalization group corrections

We consider the application of quantum corrections computed using renormalization group arguments in the astrophysical domain and show that, for the most natural interpretation of the renormalization group scale parameter, a gravitational coupling parameter G varying 10−7 of its value across a galaxy (which is roughly a variation of 10−12 per light-year) is sufficient to generate galaxy rotation curves in agreement with the observations. The quality of the resulting fit is similar to the Isothermal profile quality once both the shape of the rotation curve and the mass-to-light ratios are considered for evaluation. In order to perform the analysis, we use recent high quality data from nine regular disk galaxies. For the sake of comparison, the same set of data is modeled also for the Modified Newtonian Dynamics (MOND) and for the recently proposed Scalar Tensor Vector Gravity (STVG). At face value, the model based on quantum corrections clearly leads to better fits than these two alternative theories.

Phenomenology of supersymmetry with scalar sequestering

The defining feature of scalar sequestering is that the minimal supersymmetric standard model squark and slepton masses as well as all entries of the scalar Higgs mass matrix vanish at some high scale. This ultraviolet boundary condition---scalar masses vanish while gaugino and Higgsino masses are unsuppressed---is independent of the supersymmetry breaking mediation mechanism. It is the result of renormalization group scaling from approximately conformal strong dynamics in the hidden sector. We review the mechanism of scalar sequestering and prove that the same dynamics which suppresses scalar soft masses and the ${B}_{\ensuremath{\mu}}$ term also drives the Higgs soft masses to $\ensuremath{-}|\ensuremath{\mu}{|}^{2}$. Thus the supersymmetric contribution to the Higgs mass matrix from the $\ensuremath{\mu}$ term is exactly canceled by the soft masses. Scalar sequestering has two tell-tale predictions for the superpartner spectrum in addition to the usual gaugino mediation predictions: Higgsinos are much heavier ($\ensuremath{\mu}\ensuremath{\gtrsim}\mathrm{TeV}$) than scalar Higgses (${m}_{A}\ensuremath{\sim}\mathrm{\text{few hundred}}\text{ }\text{ }\mathrm{GeV}$), and third generation scalar masses are enhanced because of new positive contributions from Higgs loops.

Reparameterization invariance and RG equations: extension of the local potential approximation

Equations related to the Polchinski version of the exact renormalization group (RG) equations for scalar fields which extend the local potential approximation to first order in a derivative expansion, and which maintain reparameterization invariance, are postulated. Reparameterization invariance ensures that the equations determine the anomalous dimension η unambiguously and the equations are such that the result is exact to O(ε2) in an ε-expansion for any multi-critical fixed point. It is also straightforward to determine η numerically. When the dimension d = 3 numerical results for a wide range of critical exponents are obtained in theories with O(N) symmetry, for various N and for ranges of η, are obtained within the local potential approximation. The associated η, which follows from the derivative approximation described here, is found for various N. The large N limit of the equations is also analysed. A corresponding discussion is also given in a perturbative RG framework and scaling dimensions for derivative operators are calculated to first order in ε.