Showing papers on "Electroweak interaction published in 2013"
TL;DR: In this article, the parameters of the Higgs potential, the top Yukawa coupling and the electroweak gauge couplings were extracted from data with full 2-loop NNLO precision.
Abstract: We extract from data the parameters of the Higgs potential, the top Yukawa coupling and the electroweak gauge couplings with full 2-loop NNLO precision, and we extrapolate the SM parameters up to large energies with full 3-loop NNLO RGE precision. Then we study the phase diagram of the Standard Model in terms of high-energy parameters, finding that the measured Higgs mass roughly corresponds to the minimum values of the Higgs quartic and top Yukawa and the maximum value of the gauge couplings allowed by vacuum metastability. We discuss various theoretical interpretations of the near-criticality of the Higgs mass.
1,248 citations
TL;DR: In this paper, the results of the four LEP experiments were combined to determine fundamental properties of the W boson and the electroweak theory, including the branching fraction of W and the trilinear gauge-boson self-couplings.
684 citations
TL;DR: In this article, the authors extend and explore the general non-relativistic effective theory of dark matter (DM) direct detection and find several operators which lead to novel nuclear responses, which differ significantly from the standard minimal WIMP cases in their relative coupling strengths to various elements.
Abstract: We extend and explore the general non-relativistic effective theory of dark matter (DM) direct detection. We describe the basic non-relativistic building blocks of operators and discuss their symmetry properties, writing down all Galilean-invariant operators up to quadratic order in momentum transfer arising from exchange of particles of spin 1 or less. Any DM particle theory can be translated into the coefficients of an effective operator and any effective operator can be simply related to most general description of the nuclear response. We find several operators which lead to novel nuclear responses. These responses differ significantly from the standard minimal WIMP cases in their relative coupling strengths to various elements, changing how the results from different experiments should be compared against each other. Response functions are evaluated for common DM targets — F, Na, Ge, I, and Xe — using standard shell model techniques. We point out that each of the nuclear responses is familiar from past studies of semi-leptonic electroweak interactions, and thus potentially testable in weak interaction studies. We provide tables of the full set of required matrix elements at finite momentum transfer for a range of common elements, making a careful and fully model-independent analysis possible. Finally, we discuss embedding non-relativistic effective theory operators into UV models of dark matter.
586 citations
TL;DR: The Higgs-boson mass used to be the only unknown input parameter of the electroweak contributions to the Standard Model as mentioned in this paper, but it has been replaced by the Higgs mass recently measured at the LHC.
Abstract: The Higgs-boson mass used to be the only unknown input parameter of the electroweak contributions to $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ in the Standard Model. It enters at the two-loop level in diagrams with, e.g., top loops, $W$, or $Z$ exchange. We reevaluate these contributions, providing analytic expressions and exact numerical results for the Higgs-boson mass recently measured at the LHC. Our final result for the full Standard Model electroweak contributions is $(153.6\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$, where the remaining theory error comes from unknown three-loop contributions and hadronic uncertainties.
479 citations
TL;DR: In this article, the dimension-six operators of the SM EFT were renormalized and the renormalization group improved results can be used to study the flavor problem and to test the minimal flavor violation (MFV) hypothesis.
Abstract: We calculate the gauge terms of the one-loop anomalous dimension matrix for the dimension-six operators of the Standard Model effective field theory (SM EFT). Combining these results with our previous results for the $\lambda$ and Yukawa coupling terms completes the calculation of the one-loop anomalous dimension matrix for the dimension-six operators. There are 1350 $CP$-even and $1149$ $CP$-odd parameters in the dimension-six Lagrangian for 3 generations, and our results give the entire $2499 \times 2499$ anomalous dimension matrix. We discuss how the renormalization of the dimension-six operators, and the additional renormalization of the dimension $d \le 4$ terms of the SM Lagrangian due to dimension-six operators, lays the groundwork for future precision studies of the SM EFT aimed at constraining the effects of new physics through precision measurements at the electroweak scale. As some sample applications, we discuss some aspects of the full RGE improved result for essential processes such as $gg \to h$, $h \to \gamma \gamma$ and $h \to Z \gamma$, for Higgs couplings to fermions, for the precision electroweak parameters $S$ and $T$, and for the operators that modify important processes in precision electroweak phenomenology, such as the three-body Higgs boson decay $h \rightarrow Z \, \ell^+ \, \ell^-$ and triple gauge boson couplings. We discuss how the renormalization group improved results can be used to study the flavor problem in the SM EFT, and to test the minimal flavor violation (MFV) hypothesis. We briefly discuss the renormalization effects on the dipole coefficient $C_{e\gamma}$ which contributes to $\mu \to e \gamma$ and to the muon and electron magnetic and electric dipole moments.
417 citations
TL;DR: In this paper, the effective Lagrangian that describes a light Higgs-like boson was revisited to better clarify a few issues which were not exhaustively addressed in the previous literature.
Abstract: We reconsider the effective Lagrangian that describes a light Higgs-like boson and better clarify a few issues which were not exhaustively addressed in the previous literature. In particular we highlight the strategy to determine whether the dynamics responsible for the electroweak symmetry breaking is weakly or strongly interacting. We also discuss how the effective Lagrangian can be implemented into automatic tools for the calculation of Higgs decay rates and production cross sections.
398 citations
TL;DR: In this paper, the authors present a first appraisal of the salient features of the TLEP physics potential, to serve as a baseline for a more extensive design study, and present a combination of TLEp and the VHE-LHC offers, for a great cost effectiveness, the best precision and the best search reach of all options presently on the market.
Abstract: The discovery by the ATLAS and CMS experiments of a new boson with mass around 125 GeV and with measured properties compatible with those of a Standard-Model Higgs boson, coupled with the absence of discoveries of phenomena beyond the Standard Model at the TeV scale, has triggered interest in ideas for future Higgs factories. A new circular e+e- collider hosted in a 80 to 100 km tunnel, TLEP, is among the most attractive solutions proposed so far. It has a clean experimental environment, produces high luminosity for top-quark, Higgs boson, W and Z studies, accommodates multiple detectors, and can reach energies up to the t-tbar threshold and beyond. It will enable measurements of the Higgs boson properties and of Electroweak Symmetry-Breaking (EWSB) parameters with unequalled precision, offering exploration of physics beyond the Standard Model in the multi-TeV range. Moreover, being the natural precursor of the VHE-LHC, a 100 TeV hadron machine in the same tunnel, it builds up a long-term vision for particle physics. Altogether, the combination of TLEP and the VHE-LHC offers, for a great cost effectiveness, the best precision and the best search reach of all options presently on the market. This paper presents a first appraisal of the salient features of the TLEP physics potential, to serve as a baseline for a more extensive design study.
341 citations
01 Apr 2013
TL;DR: In this article, leptogenesis in the context of type-II seesaw in the case in which in addition to the scalar electroweak triplet decays the lepton asymmetry is also induced by right-handed neutrino decays (mild hierarchical scenarios).
Abstract: We discuss leptogenesis in the context of type-II seesaw in the case in which in addition to the scalar electroweak triplet decays the lepton asymmetry is also induced by right-handed neutrino decays (mild hierarchical scenarios). We show that within this setup, depending on the relative sizes of the relevant parameters, one can identify three classes of generic models, each one with its own consequences for leptogenesis.
314 citations
TL;DR: In this article, the parameters of the Higgs potential, the top Yukawa coupling and the electroweak gauge couplings were extracted from data with full 2-loop NNLO precision.
Abstract: We extract from data the parameters of the Higgs potential, the top Yukawa coupling and the electroweak gauge couplings with full 2-loop NNLO precision, and we extrapolate the SM parameters up to large energies with full 3-loop NNLO RGE precision. Then we study the phase diagram of the Standard Model in terms of high-energy parameters, finding that the measured Higgs mass roughly corresponds to the minimum values of the Higgs quartic and top Yukawa and the maximum value of the gauge couplings allowed by vacuum metastability. We discuss various theoretical interpretations of the near-criticality of the Higgs mass.
286 citations
TL;DR: The Resummino package as mentioned in this paper is a C++ and Fortran program dedicated to precision calculations in the framework of gaugino and slepton pair production at hadron colliders.
Abstract: We describe the Resummino package, a C++ and Fortran program dedicated to precision calculations in the framework of gaugino and slepton pair production at hadron colliders. This code allows to calculate transverse-momentum and invariant-mass distributions as well as total cross sections by combining the next-to-leading order predictions obtained by means of perturbative QCD with the resummation of the large logarithmic contributions arising in the small transverse-momentum region and close to the production threshold. The results computed in this way benefit from reduced theoretical uncertainties, compared to a pure next-to-leading order approach as currently employed in the experimental analyses searching for sleptons and gauginos at hadron colliders. This is illustrated by using Resummino in the context of a typical supersymmetric benchmark point dedicated to superpartner searches at the Large Hadron Collider.
281 citations
TL;DR: In this article, the connection between linear realizations of the electroweak symmetry breaking mechanism and non-linear realizations with a light Higgs-like particle present is explored, and the analysis is reduced by nature to the consideration of those flavor-conserving operators that can be written in terms of pure-gauge or gauge-Higgs ones via the equations of motion.
TL;DR: In this paper, the effects of new physics on the phenomenology of the recently discovered Higgs-like particle were studied in terms of an effective Lagrangian at the electroweak scale.
Abstract: We study the indirect effects of new physics on the phenomenology of the recently discovered “Higgs-like” particle. In a model independent framework these effects can be parametrized in terms of an effective Lagrangian at the electroweak scale. In a theory in which the SU(2)L ×U(1)Y gauge symmetry is linearly realized they appear at lowest order as dimension–six operators, containing all the SM fields including the light scalar doublet, with unknown coefficients. We discuss the choice of operator basis which allows us to make better use of all the available data on the new state, triple gauge boson vertex and electroweak precision tests, to determine the coefficients of the new operators. We illustrate our present knowledge of those by performing a global fit to the existing data which allows simultaneous determination of the eight relevant parameters quantifying the Higgs couplings to gluons, electroweak gauge bosons, bottom quarks, and tau leptons. We find that for all scenarios considered the standard model predictions for each individual Higgs coupling and observable are within the corresponding 68% CL allowed range. We finish by commenting on the implications of the results for unitarity of processes at higher energies.
TL;DR: In this article, the authors advocate an effective field theory approach to anomalous couplings, which is the natural way to extend the standard model such that the gauge symmetries are respected.
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TL;DR: The ILC Higgs White Paper as discussed by the authors provides a review of Higgs Boson theory and experiment at the International Linear Collider (ILC), including the two-Higgs doublet model, alternative approaches to electroweak symmetry breaking, and precision goals for Higgs boson experiments.
Abstract: The ILC Higgs White Paper is a review of Higgs Boson theory and experiment at the International Linear Collider (ILC). Theory topics include the Standard Model Higgs, the two-Higgs doublet model, alternative approaches to electroweak symmetry breaking, and precision goals for Higgs boson experiments. Experimental topics include the measurement of the Higgs cross section times branching ratio for various Higgs decay modes at ILC center of mass energies of 250, 500, and 1000 GeV, and the extraction of Higgs couplings and the total Higgs width from these measurements. Luminosity scenarios based on the ILC TDR machine design are used throughout. The gamma-gamma collider option at the ILC is also discussed.
TL;DR: In this article, the authors examined the extent to which the new Higgs particle's couplings resemble those of the single Higgs boson of the Standard Model and showed that these couplings are highly consistent with a dependence on particle masses that is linear to within a few %.
Abstract: There are many indirect and direct experimental indications that the new particle H discovered by the ATLAS and CMS Collaborations has spin zero and (mostly) positive parity, and that its couplings to other particles are correlated with their masses. To a high degree of confidence, it is a Higgs boson, and here we examine the extent to which its couplings resemble those of the single Higgs boson of the Standard Model. Our global analysis of its couplings to fermions and massive bosons determines that they have the same relative sign as in the Standard Model. We also show directly that these couplings are highly consistent with a dependence on particle masses that is linear to within a few %, and scaled by the conventional electroweak symmetry-breaking scale to within 10%. We also give constraints on loop-induced couplings, on the total Higgs decay width, and on possible invisible decays of the Higgs boson under various assumptions.
TL;DR: In this article, it was shown that electroweak baryogenesis can be achieved using CP violation from a dimension-6 operator that couples S to the top-quark mass, suppressed by a new physics scale that can be well above 1 TeV.
Abstract: If the Higgs boson H couples to a singlet scalar S via ?m|H|2S2, a strong electroweak phase transition can be induced through a large potential barrier that exists already at zero temperature. In this case properties of the phase transition can be computed analytically. We show that electroweak baryogenesis can be achieved using CP violation from a dimension-6 operator that couples S to the top-quark mass, suppressed by a new physics scale that can be well above 1 TeV. Moreover the singlet is a dark matter candidate whose relic density is 3% of the total dark matter density, but which nevertheless interacts strongly enough with nuclei (through Higgs exchange) to be just below the current XENON100 limits. The DM mass is predicted to be in the range 80?160 GeV.
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TL;DR: In this paper, the authors focus on a motivated parameter space of flavor and CP-conserving 2HDMs in which the couplings of all scalars to SM states are controlled by two parameters.
Abstract: The search for evidence of extended electroweak symmetry breaking has entered a new phase with the discovery of a Standard Model (SM)-like Higgs at the LHC. The measurement of Higgs couplings and direct searches for additional scalars provide complementary avenues for the discovery of new degrees of freedom. This complementarity is particularly sharp in two Higgs doublet models (2HDMs) where the couplings of the SM-like Higgs may be directly related to the LHC signals of additional scalars. In this work we develop a strategy for searching for the second Higgs doublet given the LHC signals of the recently discovered SM-like Higgs. We focus on a motivated parameter space of flavor- and CP-conserving 2HDMs in which the couplings of all scalars to SM states are controlled by two parameters. We construct fits in this parameter space to the signals of the SM-like Higgs and translate these fits into signal expectations for future measurements of both the SM-like Higgs and additional scalars, identifying the most promising search channels for discovery or exclusion of new physics. When kinematically accessible, decays of the heavy neutral scalar Higgs to two light Higgs scalars, $H \to hh$, and decays of the pseudoscalar Higgs to a light Higgs scalar and $Z$ boson, $A \to Zh$, provide promising avenues for discovery even when the couplings of the light Higgs are within a few percent of SM predictions. When the couplings of the light Higgs are exceptionally close to those of the SM, decays of heavier neutral scalars to $\gamma \gamma$ and $\tau^+ \tau^-$ become particularly important for discovery.
TL;DR: The method is based on the understanding of the invariant mass distribution of the final-state jet in the singular limit from effective field theory and can be used to study arbitrary infrared-safe observables of top-quark decay with the highest perturbative accuracy.
Abstract: We present the complete calculation of the top-quark decay width at next-to-next-to-leading order in QCD, including next-to-leading electroweak corrections as well as finite bottom quark mass and $W$ boson width effects. In particular, we also show the first results of the fully differential decay rates for the top-quark semileptonic decay $t\ensuremath{\rightarrow}{W}^{+}({l}^{+}\ensuremath{
u})b$ at next-to-next-to-leading order in QCD. Our method is based on the understanding of the invariant mass distribution of the final-state jet in the singular limit from effective field theory. Our result can be used to study arbitrary infrared-safe observables of top-quark decay with the highest perturbative accuracy.
TL;DR: In this article, the fit of electroweak precision observables within the Standard Model with a 126 GeV Higgs boson was performed, comparing the results with theoretical predictions and discuss the impact of recent experimental and theoretical improvements.
Abstract: We perform the fit of electroweak precision observables within the Standard Model with a 126 GeV Higgs boson, compare the results with the theoretical predictions and discuss the impact of recent experimental and theoretical improvements. We introduce New Physics contributions in a model-independent way and fit for the S, T and U parameters, for the ϵ
1,2,3,b
ones, for modified $ Zb\overline{b} $
couplings and for a modified Higgs coupling to vector bosons. We point out that composite Higgs models are very strongly constrained. Finally, we compute the bounds on dimension-six operators relevant for the electroweak fit.
TL;DR: In this paper, a simple extension of the standard model where the weak scale is dynamically generated together with an automatically stable vector is proposed, which predicts one extra scalar, detectable at colliders, which triggers a first order dark/electroweak cosmological phase transition with production of gravitational waves.
Abstract: Assuming that naturalness should be modified by ignoring quadratic divergences, we propose a simple extension of the standard model where the weak scale is dynamically generated together with an automatically stable vector. Identifying it as thermal dark matter, the model has one free parameter. It predicts one extra scalar, detectable at colliders, which triggers a first-order dark/electroweak cosmological phase transition with production of gravitational waves. Vacuum stability holds up to the Planck scale.
TL;DR: In this paper, the authors review the mechanism of electroweak baryogenesis and derive quantum transport equations from first principles within the Schwinger-Keldysh formalism, emphasizing the importance of the semiclassical force approach.
Abstract: We review the mechanism of electroweak baryogenesis. Our focus is on the derivation of quantum transport equations from first principles within the Schwinger–Keldysh formalism. We emphasize the importance of the semiclassical force approach, which provides reliable predictions in most models. In light of recent electric dipole moment measurements and given the results on new physics searches from collider experiments, the status of electroweak baryogenesis is discussed in a variety of models.
TL;DR: In this article, a comprehensive and comparative analysis of new electroweak physics effects in di-Higgs and di−Higgs+jet production is performed, where the newly discovered Higgs candidate is interpreted as a pseudo-Nambu-Goldstone boson.
Abstract: Multi-Higgs production provides a phenomenologically clear window to the electroweak symmetry-breaking sector. We perform a comprehensive and comparative analysis of new electroweak physics effects in di-Higgs and di−Higgs+jet production. In particular, we discuss resonant di-Higgs phenomenology, which arises in the Higgs portal model and in the minimal supersymmetric Standard Model at small tan β, and nonresonant new-physics contributions to di-Higgs production in models where the newly discovered Higgs candidate is interpreted as a pseudo-Nambu-Goldstone boson. We show that, for all these scenarios, a measurement of the di-Higgs and di−Higgs+jet final states provides an accessible and elaborate handle to understand electroweak symmetry breaking in great detail.
TL;DR: In this article, a minimal viable extension of the standard model with classical scale symmetry was constructed, and the scale-invariant and CP-symmetric Higgs potential generated radiative electroweak symmetry breaking.
TL;DR: In this article, it was shown that the electroweak vacuum can actually be very short-lived, contrary to the conclusion that follows from the flat spacetime analysis, and that the Higgs vacuum is unstable unless the rate of inflation is low enough: H inf ≲ 10 9 − 10 12 GeV.
TL;DR: In this article, a scan over an extensive region of their parameter space is performed, showing that a strongly first-order phase transition favours a light neutral scalar with SM-like properties, together with a heavy pseudo-scalar and a mass hierarchy in the scalar sector.
Abstract: The nature of the electroweak phase transition in two-Higgs-doublet models is revisited in light of the recent LHC results. A scan over an extensive region of their parameter space is performed, showing that a strongly first-order phase transition favours a light neutral scalar with SM-like properties, together with a heavy pseudo-scalar (m_A^0 > 400 GeV) and a mass hierarchy in the scalar sector, m_H^+ gamma gamma decay channel and find that an enhancement in the branching ratio is allowed, and in some cases even preferred, when a strongly first-order phase transition is required.
TL;DR: In this article, it was shown that electroweak vacuum stability is at present allowed and discussed the associated theoretical and experimental errors and the prospects for its future tests, and the boundary conditions allowing for the existence of a shallow false minimum slightly below the Planck scale, which is a stable configuration that might have been relevant for primordial inflation.
Abstract: The measurements of the Higgs boson and top-quark masses can be used to extrapolate the Standard Model Higgs potential at energies up to the Planck scale. Adopting a next-to-next-to-leading-order renormalization procedure, we (i) find that electroweak vacuum stability is at present allowed and discuss the associated theoretical and experimental errors and the prospects for its future tests, (ii) determine the boundary conditions allowing for the existence of a shallow false minimum slightly below the Planck scale, which is a stable configuration that might have been relevant for primordial inflation, and (iii) derive a conservative upper bound on type-I seesaw right-handed neutrino masses, following from the requirement of electroweak vacuum stability.
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TL;DR: In this paper, the experimental constraints on the parameters of the Higgs effective Lagrangian were updated with the most recent LHC Higgs data in all available search channels with electroweak precision observables.
Abstract: We update the experimental constraints on the parameters of the Higgs effective Lagrangian. We combine the most recent LHC Higgs data in all available search channels with electroweak precision observables from SLC, LEP-1, LEP-2, and the Tevatron. Overall, the data are perfectly consistent with the 126 GeV particle being the Standard Model Higgs boson. The Higgs coupling to W and Z bosons relative to the Standard Model one is constrained in the range [0.98, 1.08] at 95% confidence level, independently of the values of other Higgs couplings. Higher-order Higgs couplings to electroweak gauge bosons are also well constrained by a combination of LHC Higgs data and electroweak precision tests.
TL;DR: In this article, the authors study the impact of perturbative unitarity limits, renormalization group equations analysis, and experimental constraints on a Higgs singlet extension of the Standard Model (SM).
Abstract: In this article we propose an overview on the current theoretical and experimental limits on a Higgs singlet extension of the Standard Model (SM). We assume that the boson which has recently been observed by the LHC experiments is the lightest Higgs boson of such a model, while for the second Higgs boson we consider a mass range of $600\text{ }\text{ }\mathrm{GeV}\ensuremath{\le}{m}_{H}\ensuremath{\le}1\text{ }\text{ }\mathrm{TeV}$, where our model directly corresponds to a benchmark scenario of the heavy Higgs working group. In this light, we study the impact of perturbative unitarity limits, renormalization group equations analysis, and experimental constraints (electroweak precision tests, measurements of the observed light Higgs coupling strength at the Large Hadron Collider). We show that, in the case of no additional hidden sector contributions, the largest constraints for higher Higgs masses stem from the assumption of perturbativity as well as vacuum stability for scales of the order of the SM metastability scale, and that the allowed mixing range is severely restricted. We discuss implications for current LHC searches in the singlet extension, especially the expected suppression factors for SM-like decays of the heavy Higgs. We present these results in terms of a global scaling factor $\ensuremath{\kappa}$ as well as the total width $\ensuremath{\Gamma}$ of the new scalar.
TL;DR: In this paper, the authors present full next-to-leading order predictions for the production cross sections and distributions of on-shell massive gauge boson pair production in the Standard Model, including the QCD and electroweak corrections.
Abstract: Electroweak gauge boson pair production is one of the most important Standard Model processes at the LHC, not only because it is a benchmark process but also by its ability to probe the electroweak interaction directly. We present full next-to-leading order predictions for the production cross sections and distributions of on-shell massive gauge boson pair production in the Standard Model. This includes the QCD and electroweak (EW) corrections. We study the hierarchy between the different channels when looking at the size of the QCD gluon-quark-induced processes and the EW photon-quark-induced processes and provide the first comprehensive explanation of this hierarchy thanks to analytical leading-logarithmic results. We also provide a detailed study of the theoretical uncertainties affecting the total cross section predictions that stem from scale variation, parton distribution function and ${\ensuremath{\alpha}}_{s}$ errors. We then compare with the present LHC data.
TL;DR: In this article, a model of a confining dark sector, dark technicolor, that communicates with the Standard Model through the Higgs portal is proposed, and the electroweak scale is generated dynamically.
Abstract: We propose a model of a confining dark sector, dark technicolor, that communicates with the Standard Model through the Higgs portal. In this model electroweak symmetry breaking and dark matter share a common origin, and the electroweak scale is generated dynamically. Our motivation to suggest this model is the absense of evidence for new physics from recent LHC data. Although the conclusion is far from certain at this point, this lack of evidence may suggest that no mechanism exists at the electroweak scale to stabilise the Higgs mass against radiative corrections from UV physics. The usual reaction to this puzzling situation is to conclude that the stabilising new physics is either hidden from us by accident, or that it appears at energies that are currently inaccessible, such that nature is indeed fine-tuned. In order to re-examine the arguments that have lead to this dichotomy, we review the concept of naturalness in effective field theories, discussing in particular the role of quadratic divergences in relation to different energy scales. This leads us to suggest classical scale invariance as a guidline for model building, implying that explicit mass scales are absent in the underlying theory.