Hadrons are particles composed of elementary quarks and gluons, which have strong interactions described by Quantum Chromodynamics (QCD); examples are protons and neutrons, which bind to form atomic nuclei. In contrast, photons are usually thought of as the elementary force carriers of quantum electrodynamics (QED). However, at the quantum level a photon can fluctuate into a quark antiquark pair. At sufficiently high energies these virtual quarks can become real, physical particles by interacting with other particles, in particular with other hadrons. In this way photons with energies exceeding a few GeV acquire properties of a hadron. Resolved photon processes are reactions that probe these hadronic properties. These processes often dominate the production of hadronic final states, including jets (sprays of collimated hadrons), at electron–proton and electron–positron colliders. Implications of this for backgrounds at future high–energy lepton colliders remain poorly understood.

The Standard Model Effective Field Theory (SMEFT) is constrained by current LHC data. Supposedly extensions of the Standard Model (SM) involving heavy particles can be constrained by matching onto the SMEFT. However, the reliability of these indirect constraints compared to those derived directly from the UV model remains an open question. In this paper, we investigate whether 4-quark operators can accurately capture the effects of an R-parity-violating (RPV) supersymmetric model on the production of pairs of top quarks, for parameters that satisfy all known constraints and lead to measurable effects. We assume that the sbottom is the lightest supersymmetric particle and focus on its interaction with a light quark and a top quark; the sbottom thus acts like a specific diquark. The 4-quark operators arise by integrating out the sbottom at tree level. We analyze measurements of inclusive top pair production by the CMS and ATLAS collaborations. We find that the 4-quark operators can accurately describe the RPV model's effects only for very heavy sbottom squarks, where the effects are well below the sensitivity of LHC experiments for all values of the RPV coupling that satisfy unitarity constraints. Therefore present or near-future bounds on this RPV model can not be derived from SMEFT analyses.

Recent measurements from the Atacama Cosmology Telescope (ACT), combined with Planck and DESI data, suggest a higher value for the spectral index n_s. This places Starobinsky inflation at the edge of the 2σ constraints for a number of e-folds N_⋆ around 60 when using the usual analytical approximations. We present refined predictions for Starobinsky inflation that go beyond the commonly used analytical approximations. By evaluating the model with these improved expressions, we show that for N_⋆≳ 58 it remains consistent with current observational constraints at the 2σ level. Additionally, we examine the implications of the ACT results for post-inflationary reheating parameters. Specifically, we find a lower bound on the effective equation of state parameter during reheating of approximately ω≳ 0.462; this excludes purely perturbative reheating, which leads to ω≃ 0. We also show that the reheating temperature is constrained to be T_rh≲ 2 × 10^10 GeV, assuming ω≤ 1. Furthermore, we find that the predictions for the spectral index and tensor-to-scalar ratio can lie within 1σ of the recent ACT constraints if the reheating temperature satisfies 4 MeV≲ T_rh≲ 10 GeV for 0.8 ≲ ω≤ 1.

In this paper, we study the inflection point inflation generated by a polynomial superpotential and a canonical K & auml;hler potential under the supergravity framework, where only one chiral superfield is needed. We find that the special form of the scalar potential limits the inflationary Hubble parameter to values less than or similar to 10(10) GeV and the inflaton mass to less than or similar to 10(11) GeV. We obtain analytic results for small field cases and present numerical results for large field ones. We find the tensor-to-scalar ratio r < 10(-8) is always suppressed in these models, while the running of spectral index alpha approximate to O(-10(-3)) may be testable in next-generation CMB experiments. We also discuss the possible effects of a SUSY breaking Polonyi term presented in the superpotential where we find a general upper bound for the SUSY breaking scale for a given value of the Hubble parameter.

In this work, we investigate the post-inflationary dynamics of a simple single-field model with a renormalizable inflaton potential featuring a near-inflection point at a field value ϕ 0 . Due to the concave shape of the scalar potential, the effective mass of the inflaton becomes imaginary during as well as for some period after slow-roll inflation. As a result, in the initial reheating phase, where the inflaton oscillates around its minimum with a large amplitude, some field fluctuations grow exponentially; this effect becomes stronger at smaller ϕ 0 . This aspect can be analyzed using the Floquet theorem. We also analytically estimate the back reaction time after which the perturbations affect the evolution of the average inflaton field. In order to fully analyze this non-perturbative regime, we perform a (classical) lattice simulation, which reveals that the exponential growth of field fluctuations can fragment the system. This leads to a large amount of non-Gaussianity at very small scales, but the equation of state remains close to matter-like. The evolution of the background field throughout the fragmentation phase can be understood using the Hartree approximation. For sufficiently small ϕ 0 soliton-like objects, called oscillons in the literature, are formed. This leads to areas with high local over-density, δρ ≫ ρ̅ where ρ̅ is the average energy density. We speculate that this could lead to the formation of light primordial black holes, with lifetime ≳ 10 -19 sec. Other possibly observational consequences, in particular gravitational waves in the MHz–GHz range, are discussed as well. Although a complete analytical study is difficult in our case, we obtain a power law scaling for the potential observables on ϕ 0 .

Polynomial inflation is a very simple and well motivated scenario. A potential with a concave ``almost'' saddle point at field value $\phi = \phi_0$ fits well the cosmic microwave background (CMB) data and makes testable predictions for the running of the spectral index and the tensor to scalar ratio. In this work we analyze leptogenesis in the polynomial inflation framework. We delineate the allowed parameter space giving rise to the correct baryon asymmetry as well as being consistent with data on neutrino oscillations. To that end we consider two different reheating scenarios. $(i)$ If the inflaton decays into two bosons, the reheating temperature can be as high as $T_\text{rh} \sim 10^{14}$ GeV without spoiling the flatness of the potential, allowing vanilla $N_1$ thermal leptogenesis to work if $T_\text{rh}> M_1$ where $N_1$ is the lightest right--handed neutrino and $M_1$ its mass. Moreover, if the dominant decay of the inflaton is into Higgs bosons of the Standard Model, we find that rare three--body inflaton decays into a Higgs boson plus one light and one heavy neutrino allow leptogenesis even for $T_\text{rh} < M_1$ if the inflaton mass is of order $10^{12}$ GeV or higher; in the polynomial inflation scenario this requires $\phi_0 \gtrsim 2.5~M_P$. This novel mechanism of non--thermal leptogenesis is quite generic, since the coupling leading to the three--body final state is required in the type I see--saw mechanism. $(ii)$ If the inflaton decays into two fermions, the flatness of the potential implies a lower reheating temperature. In this case inflaton decay to two $N_1$ still allows successful non--thermal leptogenesis if $\phi_0 \gtrsim 0.1~M_P$ and $T_\text{rh} \gtrsim 10^{6}$ GeV.

Abstract Interactions between Dark Matter (DM) and nucleons relevant for direct search experiments can be organised in a model independent manner using a Galiliean invariant, non-relativistic effective field theory (NREFT). Here one expands the interactions in powers of the momentum transfer $$ \overrightarrow{q} $$ q → and DM velocity $$ \overrightarrow{v} $$ v → . This approach generates many operators. The potentially most important subleading operators are odd under T, and can thus only be present in a theory with CP violating interactions. We consider two such operators, called $$ \mathcal{O} $$ O 10 and $$ \mathcal{O} $$ O 11 in the literature, in simplified models with neutral spin−0 mediators; the couplings are chosen such that the coefficient of the leading spin independent (SI) operator, which survives for $$ \overrightarrow{v} $$ v → → 0, vanishes at tree level. However, it is generically induced at the next order in perturbation theory. We perform a numerical comparison of the number of scattering events between interactions involving the T−odd operators and the corresponding loop induced SI contributions. We find that for “maximal” CP violation the former can dominate over the latter. However, in two of the three models we consider, an electric dipole moment of the neutron (nEDM) is induced at two-loop order. We find that the experimental bound on the nEDM typically leads to undetectably small rates induced by $$ \mathcal{O} $$ O 10. On the other hand, the model leading to a nonvanishing coefficient of $$ \mathcal{O} $$ O 11 does not induce an nEDM.

In many well-motivated models of the electroweak scale, cascade decays of new particles can result in highly boosted hadronic resonances (e.g. $Z/W/h$). This can make these models rich and promising targets for recently developed resonant anomaly detection methods powered by modern machine learning. We demonstrate this using the state-of-the-art CATHODE method applied to supersymmetry scenarios with gluino pair production. We show that CATHODE, despite being model-agnostic, is nevertheless competitive with dedicated cut-based searches, while simultaneously covering a much wider region of parameter space. The gluino events also populate the tails of the missing energy and $H_T$ distributions, making this a novel combination of resonant and tail-based anomaly detection.

With this article, we introduce recent, improved machine learning methods from computer vision to the problem of event classification in particle physics. Supersymmetric scalar top decays to top quarks and weak-scale bino-like neutralinos, where the neutralinos decay via the UDD operator to three quarks, are difficult to search for and therefore weakly constrained. The jet substructure of the boosted decay products can be used to differentiate signal from background events. We apply the transformer-based computer vision models otet and axi to images built from jet constituents and compare the classification performance to a more classical convolutional neural network (CNN). We find that results from computer vision translate well to physics applications, and both transformer-based models perform better than the CNN. By replacing the CNN with axi, we find an improvement of S/B by a factor of almost 2 for some neutralino masses. We show that combining this classifier with additional features results in a strong separation of background and signal. We also find that replacing a CNN with a axi model in a simple mock analysis can push the 95% C.L. exclusion limit of stop masses by about 100 and 60 GeV for neutralino masses of 100 and 500 GeV. Published by the American Physical Society 2024

Heavy long-lived particles are abundant in BSM physics and will, under generic circumstances, get to dominate the energy density of the universe. The resulting matter dominated era has to end before the onset of Big Bang Nucleosynthesis through the decay of the heavy matter component of mass M into a thermal bath of temperature T. The process of thermalization primarily involves near-collinear splittings of energetic particles into two particles with lower energy. The correct treatment of these processes requires the inclusion of coherence effects which suppress the splitting rate. We write down and numerically solve the resulting coupled Boltzmann equations including all gauge bosons and fermions of the Standard Model (SM). We then comment on the dependence of the nonthermal spectra on the ratio M/T, as well as on the matter decay rate and branching ratios into various SM particles.

Supersymmetry is an extension of the successful Standard Model of particle physics; it relies on the principle that fermions and bosons are related by a symmetry, leading to an elegant predictive structure for quantum field theory. This textbook provides a comprehensive and pedagogical introduction to supersymmetry and spinor techniques in quantum field theory. By utilising the two-component spinor formalism for fermions, the authors provide many examples of practical calculations relevant for collider physics signatures, anomalies, and radiative corrections. They present in detail the component field and superspace formulations of supersymmetry and explore related concepts, including the theory of extended Higgs sectors, models of grand unification, and the origin of neutrino masses. Numerous exercises are provided at the end of each chapter. Aimed at graduate students and researchers, this volume provides a clear and unified treatment of theoretical concepts that are at the frontiers of high energy particle physics.

In a non-standard cosmological scenario, heavy, long-lived particles, which we call moduli, dominate the energy density prior to Big Bang Nucleosynthesis. Weakly Interacting Massive Particles (WIMPs) may be produced non-thermally from moduli decays. The final relic abundance then depends on additional parameters such as the branching ratio of moduli to WIMPs and the modulus mass. This is of interest for WIMP candidates, such as a bino-like neutralino, where thermal production in standard cosmology leads to an overdensity. Previous works have shown that the correct dark matter (DM) relic density can then still be obtained if the moduli, with mass less than $10^{7}$ GeV, decay to WIMPs with a branching ratio of less than $10^{-4}$. This upper bound could easily be violated once higher order corrections, involving final states with more than two particles, are included. We compute the branching ratios of three- and four-body decays of a modulus into final states involving two DM particles for general couplings. We then apply these expressions to sparticle production within the Minimal Supersymmetric Standard Model (MSSM) with neutralino DM. We find that this upper bound on the branching ratio can be satisfied in simplified models through an appropriate choice of as yet undetermined couplings. However, in the MSSM, it requires sparticle masses to be very close to half the modulus mass, in contrast to the idea of weak-scale supersymmetry.

In this paper we introduce a light Dirac particle ψ as thermal dark matter candidate in a U(1)Lμ−Lτ model. Together with the new gauge boson X, we find a possible parameter space with mX≃20 MeV, U(1)Lμ−Lτ coupling gX≃5⋅10−4 and mψ≳mX/2 where the (g−2)μ anomaly, dark matter, the Hubble tension, and (part of) the excess of 511 keV photons from the region near the galactic center can be explained simultaneously. This model is safe from current experimental and astrophysical constraints, but can be probed by the next generation of neutrino experiments as well as low–energy e+e− colliders.

Simple monomial inflationary scenarios have been ruled out by recent observations. In this work we revisit the next simplest scenario, a single--field model where the scalar potential is a polynomial of degree four which features a concave ``almost'' saddle point. We focus on trans--Planckian field values. We reparametrize the potential, which greatly simplifies the procedure for finding acceptbale model parameters. This allows for the first comprehensive scan of parameter space consistent with recent Planck and BICEP/Keck 2018 measurements. Even for trans--Planckian field values the tensor--to--scalar ratio $r$ can be as small as $\mathcal{O}(10^{-8})$, but the model can also saturate the current upper bound. In contrast to the small--field version of this model, radiative stability does not lead to strong constraints on the parameters of the inflaton potential. For very large field values the potential can be approximated by the quartic term; as well known, this allows eternal inflation even for field energy well below the reduced Planck mass $M_{\rm Pl}$, with Hubble parameter $H \sim 10^{-2} M_{\rm Pl}$. More interestingly, we find a region of parameter space that even supports {\em two phases of eternal inflation}. The second epoch only occurs if the slope at the would--be saddle point is very small, and has $H \sim 10^{-5} M_{\rm Pl}$; it can only be realized if $r \sim 10^{-2}$, within the sensitivity range of next--generation CMB observations.

We study the influence of leptophilic dark matter interactions on decays of muons and ground state mesons in existing experiments. We consider a secluded dark sector exclusively interacting with leptons via either a (leptophilic) scalar or vector mediator. These interactions will therefore influence leptonic decays and deform the energy spectra. We first study the Michel decay of muons, μ ^+→ e^+ν _e ν̅_μ , which allow us to constrain the parameter space reasonably well. Secondly, the rare π ^± , K^± , D^± and D_s^± decays to eν will be considered. Scalar mediators would remove the Standard Model helicity suppression, so that strong constraints can be derived. The resulting bounds on the couplings of the light mediators to electrons and muons still turn out to be somewhat weaker than those from searches at low-energy e^+e^- colliders and the magnetic moment of the muon, respectively. Finally, we show that kaon and pion decays basically exclude a “Co-SIMP” scenario where a scalar dark matter particle has a dimension-5 coupling to electrons.

Extending the Standard Model (SM) by a U(1)_L_μ-L_τ group gives potentially significant new contributions to g_μ-2, allows the construction of realistic neutrino mass matrices, incorporates lepton universality violation, and offers an anomaly-free mediator for a Dark Matter (DM) sector. In a recent analysis we showed that published LHC searches are not very sensitive to this model. Here we apply several Machine Learning (ML) algorithms in order to distinguish this model from the SM using simulated LHC data. In particular, we optimize the 3μ-signal, which has a considerably larger cross section than the 4μ-signal. Furthermore, since the 2-muon plus missing E_T final state gets contributions from diagrams involving DM particles, we optimize it as well. We find greatly improved sensitivity, which already for 36 fb^-1 of data exceeds the combination of published LHC and non-LHC results. We also emphasize the usefulness of Boosted Decision Trees which, unlike Neural Networks, easily allow to extract additional information from the data which directly connect to the theoretical model through feature importance. The same scheme could be used to analyze other models.

The self coupling $\lambda$ of the Higgs boson in the Standard Model may show critical behavior, i.e. the Higgs potential may have a point at an energy scale $\sim 10^{17-18}$ GeV where both the first and second derivatives (almost) vanish. In this case the Higgs boson can serve as inflaton even if its nonminimal coupling to the curvature scalar is only ${\cal O}(10)$, thereby alleviating concerns about the perturbative unitarity of the theory. We find that just before the Higgs as inflaton enters the flat region of the potential the usual slow--roll conditions are violated. This leads to "overshooting" behavior, which in turn strongly enhances scalar curvature perturbations because of the excitation of entropic (non--adiabatic) perturbations. For appropriate choice of the free parameters these large perturbations occur at length scales relevant for the formation of primordial black holes. Even if these perturbations are not quite large enough to trigger copious black hole formation, they source second order tensor perturbations, i.e. primordial gravitational waves; the corresponding energy density can be detected by the proposed space-based gravitational wave detectors DECIGO and BBO.

In the minimal supersymmetric extension of the Standard Model (MSSM) the Higgsino mass parameter mu appears both in the masses of the Higgs bosons and in the neutralino mass matrix. Electroweak finetuning therefore prefers small values of vertical bar mu vertical bar. On the other hand, binolike neutralinos make a good dark matter candidate. We show that current direct search limits then impose a strong lower bound on vertical bar mu vertical bar in particular for mu > 0 or if the masses of the heavy Higgs bosons of the MSSM are near their current limit from LHC searches; these bounds on vertical bar mu vertical bar arc typically much stronger than the ones from collider physics. There is therefore some tension between fine-tuning and neutralino dark matter in the MSSM. We also provide simple analytical expressions which in most cases closely reproduce the numerical results.

We revisit the Boltzmann equation governing the spectrum of energetic particles originating from the decay of massive progenitors during the process of thermalization. We assume that these decays occur when the background temperature T is much less than the mass M of the progenitor. We pay special attention to the IR cutoff provided by the thermal bath, and include the suppression resulting from the interference of multiple scattering reactions (LPM effect). We solve the resulting integral equation numerically, and construct an accurate analytical fit of the solutions.

We revisit the renormalizable polynomial inflection point model of inflation, focusing on the small field scenario which can be treated fully analytically. In particular, the running of the spectral index is predicted to be α = -1.43 × 10^-3 +5.56 × 10^-5(N_ CMB-65 ), which might be tested in future. We also analyze reheating through perturbative inflaton decays to either fermionic or bosonic final states via a trilinear coupling. The lower bound on the reheating temperature from successful Big Bang nucleosynthesis gives lower bounds for these couplings; on the other hand radiative stability of the inflaton potential leads to upper bounds. In combination this leads to a lower bound on the location ϕ_0 of the near inflection point, ϕ_0 > 3 · 10^-5 in Planckian units. The Hubble parameter during inflation can be as low as H_ inf∼ 1 MeV, or as high as ∼ 10^10 GeV. Similarly, the reheating temperature can lie between its lower bound of ∼ 4 MeV and about 4 · 10^8 (10^11) GeV for fermionic (bosonic) inflaton decays. We finally speculate on the "prehistory" of the universe in this scenario, which might have included an epoch of eternal inflation.