<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

The Two Higgs Doublet model extended with a complex scalar singlet (2HDMS) is a well-motivated Beyond Standard Model candidate addressing several open problems of nature. In this work, we focus on the dark matter (DM) phenomenology of the complex scalar singlet where the real part of the complex scalar obtains a vacuum expectation value. The model is characterized by an enlarged Higgs spectrum comprising six physical Higgs bosons and a pseudoscalar DM candidate. We address the impact of accommodating the 95 GeV excess on the 2HDMS parameter space and DM observables after including all theoretical and experimental constraints. Finally, we look into the prospects of this scenario at HL-LHC and future lepton colliders for a representative benchmark.

Juhi Dutta

China

Cheng Li

Gudrid Moortgat-Pick

Sheikh Farah Tabira

Julia Ziegler

Dark matter phenomenology in 2HDMS in light of the 95 GeV excess

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 anomalous ZZγ and Zγγ couplings that can be probed via Zγ production at the e + e  −  colliders. We take Standard Model Effective Field Theory (SMEFT) approach to examine these anomalous neutral triple gauge couplings in a model independent way. There are four independent dimension-8 operators that generate these gauge interactions, one of them is CP-conserving and rest three are CP-violating. We adopt optimal observable technique to extract the sensitivity at which these anomalous couplings can be probed at future e + e  −  colliders and then compare the results with the latest experimental limit obtained at the LHC. We also study the impact and advantage of beam polarization in these precision measurements. Statistical limit (95% C.L.) on individual anomalous couplings as well as the correlation between various couplings have been discussed in detail.

Probing anomalous ZZγ and Zγγ couplings at the e + e  −  colliders using optimal observable technique

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 investigate the potential of the channel mono-Higgs + missing transverse energy (MET) in yielding signals of dark matter at the high-luminosity Large Hadron Collider (LHC). As illustration, a Higgs-portal scenario has been chosen, where an extension of the Standard Model with a real scalar gauge-singlet which serves as a dark matter candidate. The phenomenological viability of this scenario has been ensured by postulating the existence of dimension-6 operators that enable cancellation in certain amplitudes for elastic scattering of dark matter in direct search experiments. These operators are found to have non-negligible contribution to the mono-Higgs signal. Thereafter, we carry out a detailed analysis of this signal, with the accompanying MET providing a useful handle in suppressing backgrounds. Signals for the Higgs decaying into both the diphoton and  $$b{\bar{b}}$$  <math> <mrow> <mi>b</mi> <mover> <mrow> <mi>b</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   channels have been studied. A cut-based simulation is presented first, optimizing over various event selection criteria. This is followed by a demonstration of how the statistical significance can be improved through analyses based on boosted decision trees and artificial neural networks.

Debabrata Bhowmik

Satyaki Bhattacharya

Ritesh Singh

The mono-Higgs + MET signal at the Large Hadron Collider: a study on the  $$\gamma \gamma $$  <math> <mrow> <mi>γ</mi> <mi>γ</mi> </mrow> </math>   and  $$b\bar{b}$$  <math> <mrow> <mi>b</mi> <mover> <mrow> <mi>b</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   final states

We study the high-scale validity of a type-X two Higgs doublet scenario, which provides an explanation of the observed value of muon (<math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>). This region allows a pseudoscalar physical state, which is well below the observed 125-GeV scalar in mass. A second neutral scalar particle can be both above and below 125 GeV in such a scenario. Admissible regions in the parameter space are obtained by using the most recent data on muon (<math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>), theoretical constraints such as low-scale perturbativity and vacuum stability, and also all experimental constraints, including the available LHC results. Among other things, both the aforesaid orders of <math><mi>C</mi><mi>P</mi></math>-even neutral scalar masses are included in our benchmark studies. Two-loop renormalization group equations are used to predict the values of various couplings at high scales, and the regions in the space spanned by low-scale parameters, which retain perturbative unitarity as well as vacuum stability up to various scales are identified. We thus conclude that such a scenario, while successfully explaining the observed muon (<math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>), can be valid up to energy scales ranging from <math><msup><mn>10</mn><mn>4</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> to the Planck scale, thus opening up directions of thought on its ultraviolet completion.