arXiv subjects

Florian Goertz

Publications and source records attributed to Florian Goertz.

At least 55 records · Page 3Linked to original sources

arXiv2018

Electroweak Symmetry Breaking without the $μ^2$ Term

We demonstrate that from a low energy perspective a viable breaking of the electroweak symmetry, as present in nature, can be achieved without the (negative sign) $μ^2$ mass term in the Higgs potential, thereby avoiding completely the appearance of relevant operators, featuring coefficients with a positive mass dimension, in the theory. We show that such a setup is self consistent and not ruled out by Higgs physics. In particular, we point out that it is the lightness of the Higgs boson that allows for the electroweak symmetry to be broken dynamically via operators of $D\geq 4$, consistent with the power expansion. Beyond that, we entertain how this scenario might even be preferred phenomenologically compared to the ordinary mechanism of electroweak symmetry breaking, as realized in the Standard Model, and argue that it can be fully tested at the LHC. In an appendix, we classify UV completions that could lead to such a setup, considering also the option of generating all scales dynamically.

hep-ph↗

arXiv2017

Recent $\boldsymbol{B}$ Physics Anomalies - a First Hint for Compositeness?

We scrutinize the recently further strengthened hints for new physics in semileptonic $B$-meson decays, focusing on the 'clean' ratios of branching fractions $R_K$ and $R_{K^\ast}$ and examining to which pattern of new effects they point to. We explore in particular the hardly considered, yet fully viable, option of new physics in the right-handed electron sector and demonstrate how a recently proposed framework of leptons in composite Higgs setups naturally solves both the $R_K$ and $R_{K^\ast}$ anomalies via a peculiar structure of new physics effects, predicted by minimality of the model and the scale of neutrino masses. Finally, we also take into account further observables, such as ${\cal B}(B_s \to μ^+μ^-)$, $ΔM_{B_s}$, and angular observables in $B \to K^{\ast} μ^+ μ^-$ decays, to arrive at a comprehensive picture of the model concerning (semileptonic) $B$ decays. We conclude that -- since it is in good agreement with the experimental situation in flavor physics and also allows to avoid ultra-light top partners -- the model furnishes a very promising scenarios of Higgs compositeness in the light of LHC data.

hep-ph↗

arXiv2017

Lepton Flavor Violation Induced by Dark Matter

Guided by gauge principles we discuss a predictive and falsifiable UV complete model where the Dirac fermion that accounts for the cold dark matter abundance in our universe induces the lepton flavor violation (LFV) decays $μ\rightarrow eγ$ and $μ\rightarrow e e e$ as well as $μ-e$ conversion. We explore the interplay between direct dark matter detection, relic density, collider probes and lepton flavor violation to conclusively show that one may have a viable dark matter candidate yielding flavor violation signatures expected to be fully probed in the upcoming of experiments. Interestingly, keeping the dark matter mass not far from the TeV, our model has an approximate prediction for the maximum LFV signal one could have while reproducing the correct dark matter relic density.

hep-ph↗

arXiv2017

Accessing Masses Beyond Collider Reach - in EFT

We demonstrate how masses of new states, beyond direct experimental reach, could nevertheless be extracted in the framework of effective field theory (EFT), given broad assumptions on the underlying UV physics, however not sticking to a particular setup nor fixing the coupling strength of the scenario. The flat direction in the $g_\ast$ vs. $M$ plane is lifted by studying correlations between observables that depend on operators with a different $\hbar$ scaling. We discuss the remaining model dependence (which is inherent even in the EFT approach to have control over the error due to the truncation of the power series), as well as prospects to test paradigms of UV physics. In particular, we provide an assessment of which correlations are best suited regarding sensitivity, give an overview of possible/expected effects in different observables, and demonstrate how perturbativity and direct search limits corner possible patterns of deviations from the SM in a given UV paradigm.

hep-ph↗

arXiv2017

On the reinterpretation of non-resonant searches for Higgs boson pairs

The detection of production of a pair of Higgs bosons before the end of LHC operation would be clear evidence of New Physics (NP). As searches for non-resonant production of Higgs pairs are being designed it is of particular importance to be able to conveniently present current experimental results in terms of limits in the most 'model-independent' fashion possible. In this article we provide an analytic parametrization of the {\it differential} Higgs-pair production at the LHC in the effective field theory (EFT) extension of the SM. It results from a fit to the theory prediction for the $gg \to hh$ cross section at the 13\,TeV at the LHC. Subsequently the resulting formula is used for a reweighing technique that allows to recast exclusion bounds from ATLAS and CMS HH$\toγγ\,b\bar{b}$ searches to any point of the considered EFT parameter space. We demonstrate with a fast simulation of the LHC detectors that with this approach it is possible to cover the continuously of the EFT parameter space, taking correctly into account the efficiencies of signal selections, without the necessity of rerunning a large number of full detector simulations. Finally, the resulting exclusion bounds are confronted to several explicit models such as setups with additional scalars, including 2HDM, vector-like fermions, and minimal composite Higgs models, mapped to the EFT.

hep-ph↗

arXiv2017

Uncovering the relation of a scalar resonance to the Higgs boson

We consider the associated production of a scalar resonance with the standard model Higgs boson. We demonstrate via a realistic phenomenological analysis that couplings of such a resonance to the Higgs boson can be constrained in a meaningful way in future runs of the LHC, providing insights on its origin and its relation to the electroweak symmetry breaking sector. Moreover, the final state can provide a direct way to determine whether the new resonance is produced predominantly in gluon fusion or quark-anti-quark annihilation. The analysis focusses on a resonance coming from a scalar field with vanishing vacuum expectation value and its decay to a photon pair. It can however be straightforwardly generalised to other scenarios.

hep-ph↗

arXiv2017

The Axiflavon

We show that solving the flavor problem of the Standard Model with a simple $U(1)_H$ flavor symmetry naturally leads to an axion that solves the strong CP problem and constitutes a viable Dark Matter candidate. In this framework, the ratio of the axion mass and its coupling to photons is related to the SM fermion masses and predicted within a small range, as a direct result of the observed hierarchies in quark and charged lepton masses. The same hierarchies determine the axion couplings to fermions, making the framework very predictive and experimentally testable by future axion and precision flavor experiments.

hep-ph↗

arXiv2016

A flavor-safe composite explanation of $R_K$

In these proceedings we discuss a flavor-safe explanation of the anomaly found in $R_K= {\cal B}(B \to K μ^+ μ^-)/{\cal B}(B \to K e^+ e^-)$ by LHCb, within the framework of composite Higgs models. We present a model featuring a non-negligible degree of compositeness for all three generations of right-handed leptons, which leads to a violation of lepton-flavor universality in neutral current interactions while other constraints from quark- and lepton-flavor physics are met. Moreoever, the particular embedding of the lepton sector considered in this setup provides a parametrically enhanded contribution to the Higgs mass that can weak considerably the need for ultra-light top partners.

hep-ph↗

arXiv2016

On the Validity of the Effective Field Theory Approach to SM Precision Tests

We discuss the conditions for an effective field theory (EFT) to give an adequate low-energy description of an underlying physics beyond the Standard Model (SM). Starting from the EFT where the SM is extended by dimension-6 operators, experimental data can be used without further assumptions to measure (or set limits on) the EFT parameters. The interpretation of these results requires instead a set of broad assumptions (e.g. power counting rules) on the UV dynamics. This allows one to establish, in a bottom-up approach, the validity range of the EFT description, and to assess the error associated with the truncation of the EFT series. We give a practical prescription on how experimental results could be reported, so that they admit a maximally broad range of theoretical interpretations. Namely, the experimental constraints on dimension-6 operators should be reported as functions of the kinematic variables that set the relevant energy scale of the studied process. This is especially important for hadron collider experiments where collisions probe a wide range of energy scales.

hep-ph↗

arXiv2016

Analytical parametrization and shape classification of anomalous HH production in the EFT approach

In this document we study the effect of anomalous Higgs boson couplings on non-resonant pair production of Higgs bosons ($HH$) at the LHC. We explore the space of the five parameters $κ_λ$, $κ_{t}$, $c_2$, $c_g$, and $c_{2g}$ in terms of the corresponding kinematics of the final state, and describe a partition of the space into a limited number of regions featuring similar phenomenology in the kinematics of $HH$ final state. We call clusters the sets of points belonging to the same region; to each cluster corresponds a representative point which we call a benchmark. We discuss a possible technique to estimate the sensitivity of an experimental search to the kinematical differences between the phenomenology of the benchmark points and the rest of the parameter space contained in the corresponding cluster. We also provide an analytical parametrization of the cross-section modifications that the variation of anomalous couplings produces with respect to standard model $HH$ production along with a recipe to translate the results into other parameter-space bases. Finally, we provide a preliminary analysis of variations in the topology of the final state within each region based on recent LHC results.

hep-ph↗

arXiv2016

Lepton Flavor and Non-Universality from Minimal Composite Higgs Setups

We present a new class of models of lepton flavor in the composite Higgs framework. Following the concept of minimality, they lead to a rich phenomenology in good agreement with the current experimental picture. Because of a unification of the right-handed leptons, our scenario is very predictive and can naturally lead to a violation of lepton-flavor universality in neutral current interactions. We will show that, in particular, the anomaly in $R_K= {\cal B}(B \to K μ^+ μ^-)/{\cal B}(B \to K e^+ e^-)$, found by LHCb, can be addressed, while other constraints from quark- and lepton-flavor physics are met. In fact, the minimal structure of the setup allows for the implementation of a very powerful flavor protection, which avoids the appearance of new sources of flavor-changing neutral currents to very good approximation. Finally, the new lepton sector provides a parametrically enhanced correction to the Higgs mass, such that the need for ultra-light top partners is weakened considerably, linking the mass of the latter with the size of the neutrino masses.

hep-ph↗

arXiv2016

Indirect Constraints on the Scalar Di-Photon Resonance at the LHC

Motivated by the tantalizing excesses recently reported in the di-photon invariant mass spectrum at the LHC, we scrutinize some implications of scalar di-photon resonances in high energy proton-proton collisions. In particular, indications of a large width impose several challenges for model building. We show how calculability and unitarity considerations severely limit possible perturbative realizations of such a signal and propose a simple criterion that can be adapted to any renormalizable model. Furthermore, we discuss correlations between a di-photon excess and precision observables, including the anomalous magnetic and electric dipole moments of quarks and leptons, neutral meson oscillations and radiative flavor changing neutral current mediated decays of heavy leptons and hadrons. We find that existing searches and measurements significantly constrain the possibilities for a scalar resonance decaying into final states involving Standard Model fermions. We propose future search strategies which could elucidate some remaining currently unconstrained decay channels and discuss possible correlations between the di-photon excess and several recently reported flavor anomalies, showing that the latter can be addressed in a new incarnation of a gauged $U(1)^\prime$ model, with the di-photon resonance being the physical remnant of the $U(1)^\prime$-breaking field.

hep-ph↗

arXiv2016

Precision Drell-Yan Measurements at the LHC and Implications for the Diphoton Excess

Precision measurements of the Drell-Yan (DY) cross section at the LHC constrain new physics scenarios that involve new states with electroweak (EW) charges. We analyze these constraints and apply them to models that can address the LHC diphoton excess at 750 GeV. We confront these findings with LEP EW precision tests and show that DY provides stronger constraints than the LEP data. While 8 TeV data can already probe some parts of the interesting region of parameter space, LHC14 results are expected to cover a substantial part of the relevant terrain. We derive the bounds from the existing data, estimate LHC14 reach and compare them to the bounds one gets from LEP and future FCC-ee precision measurements.

hep-ph↗

arXiv2016

Higgs Pair Production: Choosing Benchmarks With Cluster Analysis

New physics theories often depend on a large number of free parameters. The precise values of those parameters in some cases drastically affect the resulting phenomenology of fundamental physics processes, while in others finite variations can leave it basically invariant at the level of detail experimentally accessible. When designing a strategy for the analysis of experimental data in the search for a signal predicted by a new physics model, it appears advantageous to categorize the parameter space describing the model according to the corresponding kinematical features of the final state. A multi-dimensional test statistic can be used to gauge the degree of similarity in the kinematics of different models; a clustering algorithm using that metric may then allow the division of the space into homogeneous regions, each of which can be successfully represented by a benchmark point. Searches targeting those benchmark points are then guaranteed to be sensitive to a large area of the parameter space. In this document we show a practical implementation of the above strategy for the study of non-resonant production of Higgs boson pairs in the context of extensions of the standard model with anomalous couplings of the Higgs bosons. A non-standard value of those couplings may significantly enhance the Higgs pair production cross section, such that the process could be detectable with the data that the Large Hadron Collider will collect in Run 2.

hep-ph↗

arXiv2015

The Diboson Excess: Experimental Situation and Classification of Explanations; A Les Houches Pre-Proceeding

We examine the `diboson' excess at $\sim 2$ TeV seen by the LHC experiments in various channels. We provide a comparison of the excess significances as a function of the mass of the tentative resonance and give the signal cross sections needed to explain the excesses. We also present a survey of available theoretical explanations of the resonance, classified in three main approaches. Beyond that, we discuss methods to verify the anomaly, determining the major properties of the various surpluses and exploring how different models can be discriminated. Finally, we give a tabular summary of the numerous explanations, presenting their main phenomenological features.

hep-ph↗

arXiv2015

Probing the Charm Yukawa Coupling in Higgs + Charm Production

We propose a new method to determine the coupling of the Higgs boson to charm quarks, via Higgs production in association with a charm-tagged jet: $pp\to hc$. As a first estimate, we find that at the LHC with 3000 fb$^{-1}$ it should be possible to derive a constraint of order one, relative to the SM value of the charm Yukawa coupling. As a byproduct of this analysis, we present an estimate of the exclusive $pp \to hD^{(*)}$ electroweak cross section. Within the SM, the latter turns out to be not accessible at the LHC even in the high-luminosity phase.

hep-ph↗

arXiv2015

A naturally light Higgs without light Top Partners

We demonstrate that the inclusion of a realistic lepton sector can relax significantly the upper bound on top partner masses in minimal composite Higgs models, induced by the lightness of the Higgs boson. To that extend, we present a comprehensive survey of the impact of different realizations of the fermion sectors on the Higgs potential, with a special emphasis on the role of the leptons. The non-negligible compositeness of the $τ_R$ in a general class of models that address the flavor structure of the lepton sector and the smallness of the corresponding FCNCs, can have a significant effect on the potential. We find that, with the $τ_R$ in the symmetric representation of $SO(5)$, an increase in the maximally allowed mass of the lightest top partner of $\gtrsim 1$ TeV is possible for minimal quark setups like the MCHM$_{5,10}$, without increasing the tuning. A light Higgs boson $m_H \sim(100-200)$ GeV is a natural prediction of such models, which thus provide a new setup that can evade ultra-light top partners without ad-hoc tuning in the Higgs mass. Moreover, we advocate a more minimal realization of the lepton sector than generally used in the literature, which still can avoid light partners due to its contributions to the Higgs mass in a different and very natural way, triggered by the seesaw mechanism. This allows to construct the most economical $SO(5)/SO(4)$ composite Higgs models possible. Using both a transparent 4D approach, as well as presenting numerical results in the 5D holographic description, we demonstrate that, including leptons, minimality and naturalness do not imply light partners. Leptonic effects, not considered before, could hence be crucial for the viability of composite models.

hep-ph↗

arXiv2015

Higgs boson pair production in the D=6 extension of the SM

We derive the constraints that can be imposed on the dimension-6 effective theory extension of the Standard Model, using gluon fusion-initiated Higgs boson pair production at the LHC. We use a realistic analysis focussing on the $hh \rightarrow (b\bar{b}) ( τ^+ τ^- )$ final state, including initial-state radiation and non-perturbative effects. We include the statistical uncertainties on the signal rates as well as conservative estimates of the theoretical uncertainties. We first consider a theory containing only modifications of the trilinear coupling, through a $c_6 λ\, H^6/ v^2$ Lagrangian term, and then examine the full parameter space of the effective theory, incorporating current bounds obtained through single Higgs boson measurements. We also consider an alternative scenario, where we vary a smaller sub-set of parameters. Allowing, finally, the values of the other coefficients to vary within \textit{projected} experimental ranges, we find that the currently unbounded parameter, $c_6$, could be constrained to lie within $|c_6| \lesssim 0.6$ at 1$σ$ confidence, at the end of the high-luminosity run of the LHC (14~TeV) in the full model, and to $-0.6 \lesssim c_6 \lesssim 0.5$ in the alternative model. This study constitutes a first step towards the inclusion of multi-Higgs boson production in a full fit to the dimension-6 effective field theory framework.

hep-ph↗