Yukawa Corrections Research Articles

Phase diagram of Einstein-Weyl gravity

Thanks to their interpretation as the first order correction of general relativity at high energies, quadratic theories of gravity have gained much attention in recent times. Particular attention has been drawn to the Einstein-Weyl theory, where the addition of the squared Weyl tensor to the action opens the possibility of having non-Schwarzschild black holes in the classical spectrum of the theory. Static and spherically symmetric solutions of this theory have been studied and classified in terms of their small scales behavior; however, a classification of these solutions in terms of the asymptotic gravitational field is still lacking. In this paper we address this point and present a phase diagram of the theory, where the different types of solutions are shown in terms of their mass and the strength of a Yukawa-like correction to the gravitational field. In particular we will show that, in the case of compact stars, different equations of state imply different Yukawa corrections to the gravitational potential, with possible phenomenological implications.

Higgs boson contribution to the leading two-loop Yukawa corrections to gg → HH

We analytically compute two-loop Yukawa corrections to Higgs boson pair production in the high-energy limit. Such corrections are generated by an exchange of a Higgs boson between the virtual top quark lines. We propose two approaches to obtain expansions of the massive two-loop box integrals and show that precise results are obtained for transverse momenta of the Higgs bosons above about 150 GeV. We discuss in detail the computation of all 140 master integrals and present analytic results.

The gravitational field of a star in quadratic gravity

The characterization of the gravitational field of isolated objects is still an open question in quadratic theories of gravity.We study static equilibrium solutions for a self-gravitating fluid in extensions of General Relativity includingterms quadratic in the Weyl tensor C μνρσ and in the Ricci scalar R, as suggested by one-loop corrections to classical gravity. By the means of a shooting method procedure we link the total gravitational mass and the strength of the Yukawa corrections associated with the quadratic terms with the fluid properties at the center.It is shown that the inclusion of the C μνρσ μνρσ coupling in the lagrangian has a much strongerimpact than the R 2 correction in the determination of the radius and of the maximum mass of a compact object.We also suggest that the ambiguity in the definition of mass in quadratic gravity theories can convenientlybe exploited to detect deviations from standard General Relativity.

Scalar modes in extended hybrid metric-Palatini gravity: Weak field phenomenology

We investigate the nature of additional scalar degrees of freedom contained in extended hybrid metric-Palatini gravity, outlining the emergence of two coupled dynamical scalar modes. In particular, we discuss the weak field limit of the theory, both in the static case and from a gravitational waves perspective. In the first case, performing an analysis at the lowest order of the post parameterized Newtonian (PPN) structure of the model, we stress the settling of Yukawa corrections to the Newtonian potential. In this respect, we show that one scalar field can have long range interactions and used in the principle for mimicking dark matter effects. Concerning the gravitational waves propagation, instead, we demonstrate that is possible to have well-defined physical degrees of freedom, provided by suitable constraints on model parameters. Moreover, the study of the geodesic deviation points out the presence of breathing and longitudinal polarizations due to these novel scalar waves, which on peculiar assumptions can give rise to beating phenomena during their propagation.

Exact top Yukawa corrections to Higgs boson decay into bottom quarks

In this letter we present the results of the exact computation of contributions to the Higgs boson decay into bottom quarks that are proportional to the top Yukawa coupling. Our computation demonstrates that approximate results already available in the literature turn out to be particularly accurate for the three physical mass values of the Higgs boson, the bottom and top quarks. Furthermore, contrary to expectations, the impact of these corrections on differential distributions relevant for the searches of the Higgs boson decaying into bottom quarks at the Large Hadron Collider is rather small.

Two-loop top and bottom Yukawa corrections to the Higgs-boson masses in the complex MSSM

Results for the two-loop corrections to the Higgs-boson masses of the MSSM with complex parameters of {mathcal {O}}{left( alpha _t^2+alpha _talpha _b+alpha _b^2right) } from the Yukawa sector in the gauge-less limit are presented. The corresponding self-energies and their renormalization have been obtained in the Feynman-diagrammatic approach. The impact of the new contributions on the Higgs spectrum is investigated. Furthermore, a comparison with an existing result in the limit of the MSSM with real parameters is carried out. The new results will be included in the public code FeynHiggs.

Yukawa corrections to Higgs production in top partner models

Higgs production from gluon fusion is sensitive to the properties of heavy colored fermions and to the Yukawa couplings, (Y_F M_F)/v, of these particles to the Higgs boson. We compute the two--loop, ${\cal O}((Y_F M_F)^3/v^3)$ contributions of new high mass fermions to Higgs production. In the Standard Model, these contributions are part of the well-known electroweak corrections and are negligible. However, in models with TeV scale fermions, such as top partner or composite models, Yukawa corrections are enhanced by effects of ${\cal O}((Y_F M_F)^3/v^3)$ and are potentially significant due to the large mass of the new quarks. We examine the size of these top partner Yukawa corrections to Higgs production for parameter choices which are allowed by precision electroweak constraints.

Photon-photon interaction and the Schwinger process

We consider the tunneling processes induced by two-particle collisions. The result derived by the termal bath approach is reproduced by the classical configurations. The Coulomb and Yukawa corrections for the rate of the process are computed.

Higgs mass and vacuum stability in the Standard Model at NNLO

Abstract We present the first complete next-to-next-to-leading order analysis of the Standard Model Higgs potential. We computed the two-loop QCD and Yukawa corrections to the relation between the Higgs quartic coupling (λ) and the Higgs mass (M h ), reducing the theoretical uncertainty in the determination of the critical value of M h for vacuum stability to 1 GeV. While λ at the Planck scale is remarkably close to zero, absolute stability of the Higgs potential is excluded at 98 % C.L. for M h < 126 GeV. Possible consequences of the near vanishing of λ at the Planck scale, including speculations about the role of the Higgs field during inflation, are discussed.

Astrophysical structures from primordial quantum black holes

The characteristic sizes of astrophysical structures, up to the whole observed Universe, can be recovered, in principle, assuming that gravity is the overall interaction assembling systems starting from microscopic scales, whose order of magnitude is ruled by the Planck length and the related Compton wavelength. This result agrees with the absence of screening mechanisms for the gravitational interaction and could be connected to the presence of Yukawa corrections in the Newtonian potential which introduce typical interaction lengths. This result directly comes out from quantization of primordial black holes and then characteristic interaction lengths directly emerge from quantum field theory.

ON THE TWO-LOOP DECOUPLING CORRECTIONS TO τ-LEPTON AND b-QUARK RUNNING MASSES IN THE MSSM

Masses of heavy Standard Model (SM) fermions (top-quark, bottom-quark and tau-lepton) play an important role in the analysis of theories beyond the SM. They serve as low-energy input and reduce the parameter space of such theories. In this paper Minimal supersymmetric extension of the SM is considered and two-loop relations between known SM values of fermion masses and running parameters of the MSSM are studied within the effective theory approach. Both b-quark and τ-lepton have the same quantum numbers with respect to SU(2) group and in the MSSM acquire their masses due to interactions with the same Higgs doublet. As a consequence, for large values of tan β parameter corresponding Yukawa couplings also become large and together with tan β can significantly enhance radiative corrections. In the case of b-quark two-loop [Formula: see text] contribution to the relation between running bottom-quark mass in QCD and MSSM is known in literature. This paper is devoted to calculation of the NNLO corrections proportional to Yukawa couplings. For the τ-lepton obtained contribution can be considered as a good approximation to the full two-loop result. For the b-quark numerical analysis given in the paper shows that only the sum of strong and Yukawa corrections can play such a role.

Flavor alignment via shining in Randall-Sundrum models

We present a class of warped extra dimensional models whose flavor violating interactions are much suppressed compared to the usual anarchic case due to flavor alignment. Such suppression can be achieved in models where part of the global flavor symmetry is gauged in the bulk and broken in a controlled manner. We show that the bulk masses can be aligned with the down type Yukawa couplings by an appropriate choice of bulk flavon field representations and TeV brane dynamics. This alignment could reduce the flavor violating effects to levels which allow for a Kaluza-Klein scale as low as 2-3 TeV, making the model observable at the LHC. However, the up-type Yukawa couplings on the IR brane, which are bounded from below by recent bounds on CP violation in the D system, induce flavor misalignment radiatively. Off-diagonal down-type Yukawa couplings and kinetic mixings for the down quarks are both consequences of this effect. These radiative Yukawa corrections can be reduced by raising the flavon VEV on the IR brane (at the price of some moderate tuning), or by extending the Higgs sector. The flavor changing effects from the radiatively induced Yukawa mixing terms are at around the current upper experimental bounds. We also show the generic bounds on UV-brane induced flavor violating effects, and comment on possible additional flavor violations from bulk flavor gauge bosons and the bulk Yukawa scalars.

THE HIERARCHY PROBLEM, RADION MASS, LOCALIZATION OF GRAVITY AND 4D EFFECTIVE NEWTONIAN POTENTIAL IN STRING THEORY ON S1/Z2

In this paper, we present a systematical study of braneworlds of string theory on S1/Z2. In particular, starting with the toroidal compactification of the Neveu–Schwarz/Neveu–Schwarz sector in D + d dimensions, we first obtain an effective D-dimensional action, and then compactify one of the D - 1 spatial dimensions by introducing two orbifold branes as its boundaries. We divide the whole set of the gravitational and matter field equations into two groups, one holds outside the two branes, and the other holds on them. By combining the Gauss–Codacci and Lanczos equations, we write down explicitly the general gravitational field equations on each of the two branes, while using distribution theory we express the matter field equations on the branes in terms of the discontinuities of the first derivatives of the matter fields. Afterwards, we address three important issues: (i) the hierarchy problem; (ii) the radion mass; and (iii) the localization of gravity, the four-dimensional Newtonian effective potential and the Yukawa corrections due to the gravitational high-order Kaluza–Klein (KK) modes. The mechanism of solving the hierarchy problem is essentially the combination of the large extra dimension and warped factor mechanisms together with the tension coupling scenario. With very conservative arguments, we find that the radion mass is of the order of 10-2 GeV. The gravity is localized on the visible brane, and the spectrum of the gravitational KK modes is discrete and can be of the order of TeV. The corrections to the four-dimensional Newtonian potential from the higher order of gravitational KK modes are exponentially suppressed and can be safely neglected in current experiments. In an appendix, we also present a systematical and pedagogical study of the Gauss–Codacci equations and Israel's junction conditions across a (D - 1)-dimensional hypersurface, which can be either spacelike or timelike.

INSTANTON INDUCED CHARGED FERMION AND NEUTRINO MASSES IN A MINIMAL STANDARD MODEL SCENARIO FROM INTERSECTING D-BRANES

String instanton Yukawa corrections from Euclidean D-branes are investigated in an effective Standard Model theory obtained from the minimal U (3)× U (2)× U (1) D-brane configuration. In the case of the minimal chiral and Higgs spectrum, it is found that superpotential contributions are induced by string instantons for the perturbatively forbidden entries of the up- and down-quark mass matrices. Analogous nonperturbative effects generate heavy Majorana neutrino masses and a Dirac neutrino texture with factorizable Yukawa couplings. For this latter case, a specific example is worked out where it is shown how this texture can reconcile the neutrino data.

Bottom quark pair production in γγ collision

We study the Yukawa corrections to the γγ→b cross section in the topcolor assisted technicolor models at the photon-photon colliders. We find that, for the favorable parameters, the relative corrections from pseudo-Goldstone bosons give out a 3.17%—5.90% decrement of the cross section from the tree level when /{s/}2=500 GeV, the total relative corrections are significantly larger than the corresponding corrections in the standard model, the general two Higgs doublet model and the minimal supersymmetric standard model. So the observation of the correction to the γγ→b process at the International Linear Colliders is certainly the clue to the standard model and new physics.

Yukawa corrections from four-point functions in intersecting D6-brane models

We discuss corrections to the Yukawa matrices of the standard model (SM) fermions in intersecting D-brane models due to four-point interactions. Recently, an intersecting D-brane model has been found where it is possible to obtain correct masses and mixings for all quarks as well as the tau lepton. However, the masses for the first two charged leptons come close to the right values but are not quite correct. Since the electron and muon are quite light, it is likely that there are additional corrections to their masses which cannot be neglected. With this in mind, we consider contributions to the SM fermion mass matrices from four-point interactions. In an explicit model, we show that it is indeed possible to obtain the SM fermion masses and mixings which are a better match to those resulting from experimental data extrapolated at the unification scale when these corrections are included. These corrections may have broader application to other models.

Bb¯Hproduction at the CERN LHC: Yukawa corrections and the leading Landau singularity

At tree-level Higgs production in association with a $b$-quark pair proceeds through the small Yukawa bottom coupling in the standard model. Even in the limit where this coupling vanishes, electroweak one-loop effects, through the top-Higgs Yukawa coupling, in particular, can still trigger this reaction. This contribution is small for Higgs masses around 120 GeV but it quickly picks up for higher Higgs masses especially because the one-loop amplitude develops a leading Landau singularity and new thresholds open up. These effects can be viewed as the production of a pair of top quarks which rescatter to give rise to Higgs production through $WW$ fusion. We study the leading Landau singularity in detail. Since this singularity is not integrable when the one-loop amplitude is squared, we regulate the cross section by taking into account the width of the internal top and $W$ particles. This requires that we extend the usual box one-loop function to the case of complex masses. We show how this can be implemented analytically in our case. We study in some detail the cross section at the CERN LHC as a function of the Higgs mass and show how some distributions can be drastically affected compared to the tree-level result.

Yukawa corrections toγγ→bb¯in the topcolor assisted technicolor models

We study the Yukawa corrections to the {gamma}{gamma}{yields}bb cross section in the topcolor assisted technicolor models at the photon-photon colliders. We find that, for the favorable parameters, the relative corrections from pseudo-Goldstone bosons give out a 3.2%{approx}5.9% decrement of the cross section from the tree level when {radical}(s)=500 GeV, the contributions from new extended technicolor gauge bosons Z* and colored gauge bosons B are negligibly small, and the relative correction arising from new color-singlet heavy gauge boson Z{sup '} is less than -3.2%. Therefore, the total relative corrections are significantly larger than the corresponding corrections in the standard model, the general two Higgs doublet model, and the minimal supersymmetric standard model. Since these corrections are obvious for the International Linear Colliders, the process {gamma}{gamma}{yields}bb is really interesting in testing the standard model and searching for the signs of technicolor.

Leading Yukawa corrections to Higgs production associated with a tagged bottom-antibottom pair in the standard model at the CERN LHC

Considering the large value of the top Yukawa coupling, we investigate the leading one-loop Yukawa electroweak corrections that can be induced by the top quark in a process such as Higgs production in association with a tagged bottom-antibottom pair at the LHC. At next-to-leading order these contributions are found to be small at the LHC both for the total cross section and for the distributions. In the limit of vanishing bottom Yukawa coupling where the leading order contribution vanishes, the process can still be induced at one-loop through the top quark transition. Though this contribution which can be counted as part of the next-to-next-to-leading order correction is small for Higgs masses around 120 GeV, it quickly picks up for higher Higgs masses. This contribution represents the rescattering of the top quarks and their decay into W's leading to Higgs production through WW fusion.

Leading two-loop Yukawa corrections to the pole masses of SUSY fermions in the MSSM

We have calculated the leading Yukawa corrections to the chargino, neutralino and gluino pole masses in the DR ¯ ′ scheme in the minimal supersymmetric Standard Model (MSSM) with the full set of complex parameters. We have performed a numerical analysis for a particular point in the parameter space and found typical corrections of a few tenths of a percent thus exceeding the experimental resolution as expected at the ILC. We provide a computer program which calculates two-loop pole masses for SUSY fermions with complex parameters up to O ( α α S , Y 4 , α S Y 2 ) .