<p>In this work, we develop a numerical technique for the optimal estimation of the new physics (NP) couplings applicable to any collider process without any simplifying assumptions. This approach also provides a way to measure the quality of the NP estimates derived using standard <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>χ</mi><mn>2</mn></msup></math> analysis, and can be used to gauge the advantages of various modalities of collider design. We illustrate the techniques and arguments by considering the pair production of heavy charged fermions at an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collider.</p>

India

Subhaditya Bhattacharya

Sahabub Jahedi

Germany

Jayita Lahiri

United States

Jose Wudka

Optimal new physics estimation in the presence of standard model backgrounds

We study the high-scale validity of two kinds of two Higgs doublet models (2HDM), namely, type-II and type-X, but with a scalar SU(2) singlet dark matter (DM) candidate in addition in each case. The additional quartic couplings involving the DM particle in the scalar potential in both the scenarios bring in additional constraints from the requirement of perturbative unitarity and vacuum stability. DM relic density and direct search constraints play a crucial role in this analysis as the perturbative unitarity of the DM-Higgs portal couplings primarily decide the high scale validity of the model. We find that, within the parameter regions thus restricted, the type-II scenario must have a cutoff at around <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mn>6</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>, while the type-X scenario admits of validity up to the Planck scale. However, only those regions which are valid up to about <math><msup><mn>10</mn><mn>8</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> in type-X 2HDM is amenable to detection at the High-luminosity LHC (up to <math><mrow><mn>3000</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>), while most of the parameter space of the type-II scenario mentioned above is likely to be detectable.

Ireland

Atri Dey

Biswarup Mukhopadhaya

High scale validity of two-Higgs-doublet scenarios with a real scalar singlet dark matter

We investigate flavor violating four-Fermi Standard Model Effective Field Theory (SMEFT) operators of dimension-six that can be probed via tc   <math> <mfenced> <mrow> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>c</mi> <mo>+</mo> <mi>t</mi> <mover> <mi>c</mi> <mo>¯</mo> </mover> </mrow> </mfenced> </math>  $$ \left(\overline{t}c+t\overline{c}\right) $$  production at the multi-TeV muon collider. We study different FCNC and FCCC processes related to B, B  s , K and D decays and mixings, sensitive to these operators and constrain the corresponding couplings. The tensor operator turns out to be most tightly bound. We perform event simulation of the final state signal from tc production together with the SM background to show that operators after flavor constraint can reach the discovery limit at 10 TeV muon collider. We further adopt the optimal observable technique (OOT) to determine the optimal statistical sensitivity of the Wilson coefficients and compare them with the flavor constraints. We use the limits to predict the observational sensitivities of the rare processes like K  L  → π 0 ℓℓ, D 0 → μμ, t → cℓℓ.

Soumitra Nandi

Abhik Sarkar

Probing flavor constrained SMEFT operators through tc production at the muon collider

A dark matter (DM) having feeble interaction with the visible sector can thermalize via substantial interaction with a weakly interacting massive particle (WIMP). Such DM candidates can be categorized as pseudofeebly interacting massive particles (pFIMPs). pFIMPs have both direct and indirect search prospects via a WIMP loop. This work focuses on such possibilities. We provide all such one loop graphs stemming from pFIMP-WIMP interactions involving scalar, fermion, and vector boson particles, assuming both of them are stabilized via <math><msub><mi>Z</mi><mn>2</mn></msub><mo>⊗</mo><msubsup><mi>Z</mi><mn>2</mn><mo>′</mo></msubsup></math> symmetries. We elaborate upon a model where a fermionic WIMP has a significant Yukawa interaction with a scalar pFIMP with negligible Higgs portal coupling. We study, in detail, the loop induced direct and indirect search prospects of the pFIMP in the relic density allowed region of the model along with collider expectations at the LHC.

Dipankar Pradhan

Detection possibility of a pseudo-FIMP in the presence of a thermal WIMP

The identification and isolation of two weakly interacting massive particles (WIMP) dark matter (DM) components at colliders is of wide interest on the one hand but extremely challenging on the other, especially when the dominant signal of both DM components is of the mono-<math><mi>X</mi></math> type (<math><mi>X</mi><mo>=</mo><mi>γ</mi></math>, <math><mrow><mi>Z</mi></mrow></math>, <math><mrow><mi>H</mi></mrow></math>). After emphasizing that an <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collider is more suitable for this goal, we first identify the theoretical principles that govern the occurrence of two peaks in missing energy (<math><mi>E</mi></math>) distribution, in a double-DM scenario. We then identify a variable that rather spectacularly elicits the double-peaking behavior, namely, the plot of bin-wise statistical significance (<math><mi>S</mi><mo>/</mo><msqrt><mi>B</mi></msqrt></math>) against <math><mi>E</mi></math>. Using Gaussian fits of the histograms, we apply a set of criteria developed by us, to illustrate the above points numerically for suitable benchmarks.

Purusottam Ghosh

Biswarup Mukhopadhyaya

Mono-<math><mi>X</mi></math> signal and two component dark matter: New distinction criteria

In a two-component dark matter (DM) set up, when <math><mrow><msub><mrow><mi>DM</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></math> is in equilibrium with the thermal bath, the other <math><mrow><msub><mrow><mi>DM</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math> can be equilibrated just by sizeable interaction with <math><mrow><msub><mrow><mi>DM</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></math>, even without any connection with the visible-sector particles. We show that such DM candidates (<math><mrow><msub><mrow><mi>DM</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math>) have unique “freeze-out” characteristics impacting the relic density, direct and collider search implications, and propose to classify them as pseudofeebly interacting massive particles (pFIMP). The dynamics of pFIMP is studied in a model-independent manner by solving generic coupled Boltzmann equations (cBEQ), followed by a concrete model illustration.

Dynamics of pseudofeebly interacting massive particles in presence of thermal dark matter

We study the determination of new physics (NP) parameters using the optimal observable technique (OOT) in situations where the standard model (SM) dominates over the NP effects, and when the NP dominates over the SM contribution, using the 2-Higgs doublet model as an illustrative example; for the case of SM domination we extend our results using an effective theory parameterization of NP effects. For the case of SM dominance we concentrate on   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$  production in an e + e  −  collider, while for the case of NP dominance we consider both   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$  production and pair production of charged scalars, also in an e + e  −  collider. We discuss the effects of the efficiency of background reduction, luminosity and beam polarization, and provide a comparison of the optimal uncertainties with those obtained using a standard χ 2 analysis of (Monte Carlo generated) collider data.

Optimal determination of new physics couplings: a comparative study

We analyse the single top production in association with the Higgs at the Large Hadron Collider (LHC) using Standard Model (SM) effective operators upto dimension six. We show that the presence of effective operators can significantly alter the existing bound on the top-Higgs Yukawa coupling. We analyse events at the LHC with 35.9 and 137(140) fb −1 integrated luminosities using both cut-based and machine learning techniques to probe new physics (NP) scale and operator coefficients addressing relevant SM background reduction. The four fermi effective operator(s) that contribute to the signal, turn out to be crucial and a limit on the top-Higgs Yukawa interaction in presence of them is obtained from the present data and for future sensitivities.

Sanjoy Biswas

Kuntal Pal

Associated production of Higgs and single top at the LHC in presence of the SMEFT operators

We investigate ways of identifying two kinds of dark matter (DM) component particles at high-energy colliders. The strategy is to notice and distinguish double-peaks(humps) in the missing energy/transverse energy distribution. The relative advantage of looking for missing energy is pointed out, in view of the fact that the longitudinal component of the momentum imbalance becomes an added input. It thus turns out that an electron-positron collider is better suited for discovering a two-component DM scenario, so long as both of the components are kinematically accessible. This and a number of associated conclusions are established, using for illustration a scenario including a scalar and a spin-1/2 particle. We also formulate a set of measurable quantities which quantify the distinguishability of the two humps, defined in terms of double-Gaussian fits to the missing energy distribution. The efficacy of these variables in various regions of the parameter space is discussed, using the aforesaid model as illustration.

Distinguishing two dark matter component particles at e + e  −  colliders

We propose a minimal model based on lepton number symmetry (and violation), to address a common origin of baryon asymmetry, dark matter and neutrino mass generation. The model consists of a vectorlike fermion to constitute the dark sector, three right-handed neutrinos (RHNs) to dictate leptogenesis and neutrino mass, while an additional complex scalar is assumed to be present in the early Universe the decay of which produces both dark matter and RHNs via lepton number violating and lepton number conserving interactions respectively. Interestingly, the presence of the same scalar helps in making the electroweak vacuum stable until the Planck scale. The unnatural largeness and smallness of the parameters required to describe correct experimental limits are attributed to lepton number violation. The allowed parameter space of the model is illustrated via a numerical scan.