We explore single and double flavor-violating scalar (flavon) production at the 13 and 14 TeV LHC in an effective field theory formulation where flavons always change the flavor of the Standard Model fermions. When those scalars couple to mass, their flavor-changing couplings to top quarks and tau leptons are favored. Focusing on the mass region below the top-quark mass, we find couplings that fit the muon (<math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>) discrepancy and avoid several current experimental constraints. We determine the potential of the LHC to exclude or discover such a new physics scenario with clean signatures consisting of same-sign tau leptons and the simultaneous observation of resonances in the tau plus electron or muon invariant mass. We found that in the double production mode, effective couplings down to order <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mrow><msup><mrow><mi>TeV</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></mrow></math> can be probed for flavon masses in the 10–170 GeV range at the 14 TeV HL-LHC, but couplings down to <math><mn>0.1</mn><mtext> </mtext><mtext> </mtext><msup><mi>TeV</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> can already be excluded at 95% confidence level with data collected from the 13 TeV LHC in the same mass interval. We also explore the impact of sizeable diagonal flavon couplings on the prospects of LHC for the signals we propose.

Brazil

Alexandre Alves

Alex G. Dias

Eduardo da Silva Almeida

Diego S. V. Gonçalves

Same-sign taus signatures of maximally flavor-violating scalars at the LHC

We study the lepton-induced resonant production of color-adjoint leptons (leptogluons) at the LHC, employing the lepton parton density function of the proton. We demonstrate that this production mechanism can be useful to extend the LHC ability to search for leptogluons beyond purely quark/gluon-initiated production processes up to <math><mo>∼</mo><mn>3.5</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> leptogluon masses and <math><mi>O</mi><mo>(</mo><mn>1</mn><mo>)</mo><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> compositeness scales. Discerning leptogluons from scalar and vector leptoquarks is also possible in this channel, given a data sample containing the order of 100 signal events. We argue that the resonant channel can be combined with leptogluon pair and associated leptogluon-lepton productions to boost exclusion limits and discovery prospects at the LHC.

Spain

Oscar J. P. Éboli

Chile

F. S. Queiroz

Resonant lepton-gluon collisions at the Large Hadron Collider

We present a comprehensive study of the electroweak interactions using the available Higgs and electroweak diboson production results from LHC runs 1 and 2 as well as the electroweak precision data in terms of the dimension-six operators. Under the assumption that no new tree-level sources of flavor violation or violation of the universality of the weak current are introduced, the analysis involves 21 operators. We assess the impact of the data on kinematic distributions for the Higgs production at the LHC by comparing the results obtained by including the simplified template cross-section data with those in which only total Higgs signal strengths are considered. We also compare the results obtained when including the dimension-six anomalous contributions to order <math><mrow><mn>1</mn><mo>/</mo><msup><mrow><mi>Λ</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> and to order <math><mrow><mn>1</mn><mo>/</mo><msup><mrow><mi>Λ</mi></mrow><mrow><mn>4</mn></mrow></msup></mrow></math>. As an illustration of the LHC potential to indirectly learn about specific forms of new physics, we adapt the analysis to constrain the parameter space for a few simple extensions of the standard model which generate a subset of the dimension-six operators at tree level.

United States

M. C. Gonzalez–Garcia

Electroweak legacy of the LHC run II

The off-shell Higgs production in <math><mrow><mi>p</mi><mi>p</mi><mo>→</mo><mi>Z</mi><mi>Z</mi></mrow></math> at LHC provides at present the most direct measurement of the Higgs width in the absence of beyond the standard model contributions. Here, we analyze the impact of anomalous <math><mi>Z</mi></math> couplings to fermions on the Higgs width determination. We show that, despite these couplings being strongly constrained by the available electroweak precision data, they can substantially affect the Higgs width determination at the LHC Runs 2 and 3. Conversely, in larger integrated luminosities runs, such as those foreseen at the high luminosity LHC and high energy LHC setups, the effect of such anomalous interactions in the Higgs width measurement is minimal.

O. J. P. Éboli

M. C. Gonzalez-Garcia

Impact of fermionic operators on the Higgs boson width measurement

We obtain the partial-wave unitarity constraints on the lowest-dimension effective operators which generate anomalous quartic gauge couplings but leave the triple gauge couplings unaffected. We consider operator expansions with linear and nonlinear realizations of the electroweak symmetry and explore the multidimensional parameter space of the coefficients of the relevant operators: 18 dimension-eight operators in the linear expansion and 5 <math><mi>O</mi><mo>(</mo><msup><mi>p</mi><mn>4</mn></msup><mo>)</mo></math> operators in the derivative expansion. We study two-to-two scattering of electroweak gauge bosons and Higgs bosons, taking into account all coupled channels and all possible helicity amplitudes for the <math><mi>J</mi><mo>=</mo><mn>0</mn></math>, 1 partial waves. In general, the bounds degrade by factors of a few when several operator coefficients are considered to be nonvanishing simultaneously. However, this requires considering constraints from both <math><mi>J</mi><mo>=</mo><mn>0</mn></math> and <math><mi>J</mi><mo>=</mo><mn>1</mn></math> partial waves for some sets of operators.

Unitarity constraints on anomalous quartic couplings

We study the effect of operators generating dipole couplings of the light quarks to electroweak gauge bosons on several observables at the LHC. We start by demonstrating that the determination of the gauge- boson self-couplings from electroweak diboson production at LHC is robust under the inclusion of those quark dipole operators even when let them totally unconstrained in the analysis. Conversely, we determine the bounds that the diboson data imposes on the light-quark dipole couplings and show that they represent a significant improvement over the limits arising from <math><mi>Z</mi></math> and <math><mi>W</mi></math> electroweak precision measurements. We also explore the sensitivity of the Drell-Yan cross section determination at LHC Run 1, and the results on resonance searches in high invariant-mass lepton pair production at Run 2 to further constrain the electroweak dipole couplings of the light quarks.

N. Rosa-Agostinho

Light-quark dipole operators at the LHC

We perform a comprehensive study of the Higgs couplings, gauge boson couplings to fermions, and triple gauge boson vertices. We work in the framework of effective theories including the effects of the dimension-six operators contributing to these observables. We determine the presently allowed range for the coefficients of these operators via a 20 parameter global fit to the electroweak precision data, as well as electroweak diboson and Higgs production data from LHC runs 1 and 2. We quantify the improvement on the determination of the 20 Wilson coefficients by the inclusion of the run 2 results. In particular, we present a novel analysis of the ATLAS run <math><mrow><mn>2</mn><mtext> </mtext><mn>36.1</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> data on the transverse mass distribution of <math><msup><mi>W</mi><mo>+</mo></msup><msup><mi>W</mi><mo>−</mo></msup></math> and <math><msup><mi>W</mi><mo>±</mo></msup><mi>Z</mi></math> in the leptonic channel, which allows for stronger tests of the triple gauge boson vertices. We discuss the discrete (quasi)degeneracies existing in the parameter space of operator coefficients relevant for the Higgs couplings to fermions and gauge bosons. In particular, we show how the inclusion of the incipient <math><mi>t</mi><mi>H</mi></math> data can break those degeneracies in the determination of the top Higgs coupling. We also discuss and quantify the effect of keeping the terms quadratic in the Wilson coefficients in the analysis, and we show the importance of the Higgs data to constrain some of the operators that modify the triple gauge boson couplings in the linear regime.

Electroweak sector under scrutiny: A combined analysis of LHC and electroweak precision data

Photon-like particles are predicted in many extensions of the Standard Model. They have interactions similar to the photon, are vector bosons, and can be produced together with photons. The present paper proposes a search for such particles in the <math id="M2"><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>-</mo></mrow></msup><mo>→</mo><mi>U</mi><mi>γ</mi></math> process in a positron-on-target experiment, exploiting the positron beam of the DA<math id="M3"><mrow><mi>Φ</mi></mrow></math>NE linac at the Laboratori Nazionali di Frascati, INFN. In one year of running a sensitivity in the relative interaction strength down to ~10−6 is achievable, in the mass region from 2.5 <math id="M4"><mtext>MeV</mtext><mo>&lt;</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>U</mi></mrow></msub><mo>&lt;</mo><mn>20</mn></math> MeV. The proposed experimental setup and the analysis technique are discussed.