multi-TeV Scale Research Articles

The Λc → Λ ℓ+νℓ weak decay including new physics

We investigate the Λc → Λℓ+νℓ decay with a focus on potential new physics (NP) effects in the ℓ = μ channel. We employ an effective Hamiltonian within the framework of the Standard Model Effective Field Theory (SMEFT) to consider generalized dimension-6 semileptonic c → s operators of scalar, pseudoscalar, vector, axial-vector and tensor types. We rely on Lattice QCD (LQCD) for the hadronic transition form factors, using heavy quark spin symmetry (HQSS) to determine those that have not yet been obtained on the lattice. Uncertainties due to the truncation of the NP Hamiltonian and different implementations of HQSS are taken into account. As a result, we unravel the NP discovery potential of the Λc → Λ semileptonic decay in different observables. Our findings indicate high sensitivity to NP in lepton flavour universality ratios, probing multi-TeV scales in some cases. On the theoretical side, we identify LQCD uncertainties in axial and vector form factors as critical for improving NP sensitivity, alongside better SMEFT uncertainty estimations.

Dark matter from anomaly cancellation at the LHC

We discuss a class of theories that predict a fermionic dark matter candidate from gauge anomaly cancellation. As an explicit example, we study the predictions in theories where the global symmetry associated with baryon number is promoted to a local gauge symmetry. In this context, the symmetry-breaking scale has to be below the multi-TeV scale in order to be in agreement with the cosmological constraints on the dark matter relic density. The new physical “Cucuyo” Higgs boson in the theory has very interesting properties, decaying mainly into two photons in the low mass region, and mainly into dark matter in the intermediate mass region. We study the most important signatures at the Large Hadron Collider, evaluating the experimental bounds. We discuss the correlation between the dark matter relic density, direct detection, and collider constraints. We find that these theories are still viable and are susceptible to being probed in current, and future high-luminosity, running. Published by the American Physical Society 2024

Majorana neutrinos and dark matter from anomaly cancellation

We discuss a simple theory for neutrino masses where the total lepton number is a local gauge symmetry spontaneously broken below the multi-TeV scale. In this context, the neutrino masses are generated through the canonical seesaw mechanism and a Majorana dark matter candidate is predicted from anomaly cancellation. We discuss in great detail the dark matter annihilation channels and find out the upper bound on the symmetry-breaking scale using the cosmological bounds on the relic density. Since in this context the dark matter candidate has suppressed couplings to the Standard Model quarks, one can satisfy the direct detection bounds even if the dark matter mass is close to the electroweak scale. This theory predicts a light pseudo-Nambu-Goldstone boson (the Majoron) associated to the mechanism of neutrino mass. We discuss briefly the properties of the Majoron and the impact of the big bang nucleosynthesis bounds. Published by the American Physical Society 2024

Probing muon g-2 at a future muon collider

The 4.2\sigma4.2σ discrepancy in the (g-2)(g−2) of the muon provides a hint that may indicate that physics beyond the standard model is at play. A multi-TeV scale muon collider provides a natural testing ground for this physics. In this paper, we discuss the potential to probe the BSM parameter space that is consistent with solving the (g-2)_{\mu}(g−2)μ discrepancy in the language of the SMEFT, utilizing the statistical power provided by fitting event rates collected running at multiple energies. Our results indicate the importance of including interference between the BSM and the SM amplitudes, and illustrates how a muon collider running at a handful of lower energies and with less total collected luminosity can better significantly constrain the space of relevant SMEFT coefficients than would be possible for a single high energy run.

Radiative Majorana neutrino masses in a parity solution to the strong CP problem

The strong CP problem is solved in Parity symmetric theories, with the electroweak gauge group containing SU(2)L × SU(2)R broken by the minimal set of Higgs fields. Neutrino masses may be explained by adding the same number of gauge singlet fermions as the number of generations. The neutrino masses vanish at tree-level and are only radiatively generated, leading to larger couplings of right-handed neutrinos to Standard Model particles than with the tree-level seesaw mechanism. We compute these radiative corrections and the mixing angles between left- and right-handed neutrinos. We discuss sensitivities to these right-handed neutrinos from a variety of future experiments that search for heavy neutral leptons with masses from tens of MeV to the multi-TeV scale.

New physics interpretation of W -boson mass anomaly

The CDF Collaboration has recently reported an updated result on the $W$-boson mass measurement, showing a $7\ensuremath{\sigma}$ deviation from the standard model prediction. The discrepancy may indicate new contributions to the Fermi coupling constant. We study simple extensions of the standard model by introducing an extra scalar, fermion, or vector field. It is found that the tension implies the new physics existing in multi-TeV scales if the new coupling to the electron and/or muon is of order unity.

EFT at FASER\u03bd

We investigate the sensitivity of the FASERν detector to new physics in the form of non-standard neutrino interactions. FASERν, which will be installed 480 m downstream of the ATLAS interaction point, will for the first time study interactions of multi-TeV neutrinos from a controlled source. Our formalism — which is applicable to any current and future neutrino experiment — is based on the Standard Model Effective Theory (SMEFT) and its counterpart, Weak Effective Field Theory (WEFT), below the electroweak scale. Starting from the WEFT Lagrangian, we compute the coefficients that modify neutrino production in meson decays and detection via deep-inelastic scattering, and we express the new physics effects in terms of modified flavor transition probabilities. For some coupling structures, we find that FASERν will be able to constrain interactions that are two to three orders of magnitude weaker than Standard Model weak interactions, implying that the experiment will be indirectly probing new physics at the multi-TeV scale. In some cases, FASERν constraints will become comparable to existing limits — some of them derived for the first time in this paper — already with 150 fb−1 of data.

Baryogenesis via leptogenesis: Spontaneous B and L violation

In order to address the baryon asymmetry in the Universe one needs to understand the origin of baryon (B) and lepton (L) number violation. In this article, we discuss the mechanism of baryogenesis via leptogenesis to explain the matter-antimatter asymmetry in theories with spontaneous breaking of baryon and lepton number. In this context, a lepton asymmetry is generated through the out-of-equilibrium decays of right-handed neutrinos at the high-scale, while local baryon number must be broken below the multi-TeV scale to satisfy the cosmological bounds on the dark matter relic density. We demonstrate how the lepton asymmetry generated via leptogenesis can be converted in two different ways: a) in the theory predicting Majorana dark matter the lepton asymmetry is converted into a baryon asymmetry, and b) in the theory with Dirac dark matter the decays of right-handed neutrinos can generate lepton and dark matter asymmetries that are then partially converted into a baryon asymmetry. Consequently, we show how to explain the matter-antimatter asymmetry, the dark matter relic density and neutrino masses in theories for local baryon and lepton number.

Mixed EW-QCD leading fermionic three-loop corrections at mathcal{O} (\u03b1s\u03b12) to electroweak precision observables

Measurements of electroweak precision observables at future electron-position colliders, such as the CEPC, FCC-ee, and ILC, will be sensitive to physics at multi-TeV scales. To achieve this sensitivity, precise predictions for the Standard Model expectations of these observables are needed, including corrections at the three- and four-loop level. In this article, results are presented for the calculation of a subset of three-loop mixed electroweak-QCD corrections, stemming from diagrams with a gluon exchange and two closed fermion loops. The numerical impact of these corrections is illustrated for a number of applications: the prediction of the W-boson mass from the Fermi constant, the effective weak mixing angle, and the partial and total widths of the Z boson. Two alternative renormalization schemes for the top-quark mass are considered, on-shell and overline{mathrm{MS}} .

Boosted jet techniques for a supersymmetric scenario with gravitino LSP

Search for compressed supersymmetry at multi-TeV scale, in the presence of a light gravitino dark matter, can get sizable uplift while looking into the associated fat- jets with missing transverse momenta as a signature of the boson produced in the decay process of much heavier next-to-lightest sparticle. We focus on the hadronic decay of the ensuing Higgs and/or Z boson giving rise to at least two fat-jets and in the final state. We perform a detailed background study adopting a multivariate analysis using a boosted decision tree to provide a robust investigation to explore the discovery potential for such signal at 14 TeV LHC considering different benchmark points satisfying all the theoretical and experimental constraints. This channel provides the best discovery prospects with most of the benchmarks discoverable within an integrated luminosity of mathrm{mathcal{L}} = 200 fb−1. Kinematic observables are investigated in order to distinguish between compressed and uncompressed spectra having similar event yields.

Leading fermionic three-loop corrections to electroweak precision observables

Future electron-position colliders, such as the CEPC, FCC-ee, and ILC have the capability to dramatically improve the experimental precision for W and Z-boson masses and couplings. This would enable indirect probes of physics beyond the Standard Model at multi-TeV scales. For this purpose, one must complement the experimental measurements with equally precise calculations for the theoretical predictions of these quantities within the Standard Model, including three-loop electroweak corrections. This article reports on the calculation of a subset of these corrections, stemming from diagrams with three closed fermion loops to the following quantities: the prediction of the W-boson mass from the Fermi constant, the effective weak mixing angle, and partial and total widths of the Z boson. The numerical size of these corrections is relatively modest, but non-negligible compared to the precision targets of future colliders. In passing, an error is identified in previous results for the two-loop corrections to the Z width, with a small yet non-zero numerical impact.

Search for the SUSY electroweak sector at ep colliders

The sensitivity of future electron-proton colliders, the LHeC and FCC-eh, to weakly-produced supersymmetric particles is evaluated in this article. Supersymmetric scenarios where charginos ($\tilde{\chi}_1^{\pm}$) and neutralinos ($\tilde{\chi}_1^{0}$ and $\tilde{\chi}_2^{0}$) are nearly degenerate in mass are considered. Two sets of models, which differ in the mass of sleptons ($\tilde{\ell}$), are studied. Under the hypothesis that slepton masses are at the multi-TeV scale (``decoupled'' scenario), the production processes for charginos and neutralinos at $ep$ colliders, $p\, e^- \to j\, e^-\, \tilde{\chi} \tilde{\chi}$ with $\tilde{\chi}=\tilde{\chi}_1^{0}$, $\tilde{\chi}_1^{\pm}$ or $\tilde{\chi}_2^{0}$, are considered. For the models where slepton masses are above but close to $\tilde{\chi}_1^{\pm}$, $\tilde{\chi}_2^{0}$ masses (``compressed'' scenario), contributions from the processes $p\, e^- \to j\, \tilde{\chi}\, \tilde{e}_L^-$ and $j\, \tilde{\chi}\, \tilde{\nu}$ followed by the decays $\tilde{e}_L^- \to \tilde{\chi}_{1,2}^{0} + e^-$ and $\tilde{\nu} \to \tilde{\chi}_1^+ + e^-$ are also taken into account. These scenarios are analysed with realistic detector performance, using multivariate techniques. Effects of systematic uncertainties and electron beam polarization dependence are also discussed. The reach is found to be complementary to the one obtained at $pp$ colliders, in particular for the compressed-slepton scenario.

Mixed gluinos and sgluons from a new SU(3) gauge group

I study supersymmetric models in which the QCD gauge group is the remnant diagonal subgroup from the spontaneous breaking of an $SU(3) \times SU(3)$ gauge group at a multi-TeV scale. In renormalizable models with soft supersymmetry breaking, the scalar potential is shown to have global minima with the required gauge symmetry breaking pattern. In addition to a massive color octet vector boson, this framework predicts 3 color octet spin-0 sgluons, and 4 color octet gluinos with both Dirac and Majorana mass terms. One of the gluino mass eigenstates typically has a coupling to quark-squark pairs that is at least as large as the prediction of minimal supersymmetry, but it need not be the lightest one.

Excited quarks production at FCC and SppC pp colliders

Potential discovery, observation and exclusion limits of excited [Formula: see text] and [Formula: see text] quarks with gamma[Formula: see text]jet final state are researched at the multi-TeV scale colliders, FCC and S[Formula: see text]C in this paper. Both colliders, FCC and S[Formula: see text]C, show that excited [Formula: see text] and [Formula: see text] quarks could be discovered up to 42.1 TeV and 55.2 TeV for [Formula: see text], 30.3 TeV and 39.4 TeV for [Formula: see text] and 42.3 TeV and 55.5 TeV mass values for degenerate case [Formula: see text], respectively. The determination of the excited quarks compositeness scale is examined, which will be up to multi-PeV level. Besides these analyses, free parameters ([Formula: see text], [Formula: see text] and [Formula: see text]) are scanned from around 0.1 up to 1 that show excited quark could be discovered at dozens of TeV with even coupling constants under 0.1.

A magic magnetic field to measure the neutron electric dipole moment

New sources of CP violation beyond the Standard Model of particle physics could be revealed in the laboratory by measuring a non-zero electric dipole moment (EDM) of a spin 1/2 particle such as the neutron. Despite the great sensitivity attained after 60 years of developments, the result of the experiments is still compatible with zero. Still, new experiments have a high discovery potential since they probe new physics at the multi-TeV scale, beyond the reach of direct searches at colliders. Progress in precision on the neutron EDM is limited by a systematic effect arising from the relativistic motional field E→×v→/c2 experienced by the particles moving in the measurement chamber in combination with the residual magnetic gradients. This effect would normally forbid a significant increase of the size of the chamber, sadly hindering the increase of neutron statistics. We propose a new measurement concept to evade this limitation in a room-temperature experiment employing a mercury co-magnetometer. It consists in adjusting the static magnetic field B0 to a “magic” value which cancels the false EDM of the mercury. The magic setting is 7.2μT for a big cylindrical double-chamber of diameter 100 cm.

Interpreting the electron EDM constraint

The ACME collaboration has recently announced a new constraint on the electron EDM, |de| < 1.1 × 10−29e cm, from measurements of the ThO molecule. This is a powerful constraint on CP-violating new physics: even new physics generating the EDM at two loops is constrained at the multi-TeV scale. We interpret the bound in the context of different scenarios for new physics: a general order-of-magnitude analysis for both the electron EDM and the CP-odd electron-nucleon coupling; 1-loop SUSY, probing sleptons above 10 TeV; 2-loop SUSY, probing multi-TeV charginos or stops; and finally, new physics that generates the EDM via the charm quark or top quark Yukawa couplings. In the last scenario, new physics generates a “QULE operator” left({q}_f{overline{sigma}}^{mu nu }{overline{u}}_fright)kern0.5em cdotp kern0.5em left(ell {overline{sigma}}_{mu nu}overline{e}right) , which in turn generates the EDM through RG evolution. If the QULE operator is generated at tree level, this corresponds to a previously studied leptoquark model. For the first time, we also classify scenarios in which the QULE operator is generated at one loop through a box diagram, which include (among others) SUSY and leptoquark models. The electron EDM bound is the leading constraint on a wide variety of theories of CP-violating new physics interacting with the Higgs boson or the top quark. We argue that any future nonzero measurement of an electron EDM will provide a strong motivation for constructing new colliders at the highest feasible energies.

Top-bottom-tau Yukawa coupling unification in the MSSM plus one vectorlike family and fermion masses as IR fixed points

In the MSSM extended by a complete vectorlike family, precise top, bottom and tau Yukawa coupling unification can be achieved assuming SUSY threshold corrections which are typical for comparable superpartner masses. Furthermore, the unification is possible with a large unified coupling, implying that all three fermion masses can be simultaneously close to their IR fixed points. Assuming unified Yukawa couplings of order one or larger, the preferred common scale of new physics (superpartners and vectorlike matter) is in the 3 TeV to 30 TeV range, with larger couplings favoring smaller scales. Splitting superpartner masses from masses of vectorlike fields, the preferred scales extend in both directions. The multi-TeV scale for superpartners is compatible with and independently suggested by the Higgs boson mass.

Vacuum misalignment and pattern of scalar masses in the SU(5)/SO(5) composite Higgs model

Composite Higgs models based on SU(5)/SO(5) are characterised by the presence of custodial triplets, like the Georgi-Machacek model. We classify all the operators giving rise to the top mass and Higgs potential in presence of fermion partial compositeness, with top partners in two-index representations of SU(5). A detailed study of each operator allows us to find correlations in the couplings of Higgs and non-Higgs pseudo-Nambu-Goldstone bosons, which depend only on one, two or three independent parameters. We also analyse the Higgs potential, finding that a misalignment along the custodial invariant triplet direction is forbidden by CP conservation. Avoiding custodial breaking allows us to select a handful of feasible models, which feature universal patterns in the scalar masses related to their transformation properties under the custodial symmetry. Finally, we briefly study the LHC phenomenology of the scalars, which are always below 1 TeV even for multi-TeV condensation scales, and find promising same-sign lepton final states enriched by hard photons.

Addressing the B-physics anomalies in a fundamental Composite Higgs model

I present a model addressing coherently the naturalness problem of the electroweak scale and the observed pattern of deviations from the Standard Model in semileptonic decays of B mesons. The Higgs and the two scalar leptoquarks responsible for the B-physics anomalies, {S}_1=left(overline{mathbf{3}},mathbf{1},1/3right) and {S}_3=left(overline{mathbf{3}},mathbf{3},1/3right) , arise as pseudo Nambu-Goldstone bosons of a new strongly coupled sector at the multi-TeV scale. I focus on an explicit realization of such a dynamics in terms of a new strongly coupled gauge interaction and extra vectorlike fermions charged under it. The model presents a very rich phenomenology, ranging from flavour observables, Higgs and electroweak precision measurements, and direct searches of new states at the LHC.

Radiative bound-state formation in unbroken perturbative non-Abelian theories and implications for dark matter

We compute the cross-sections for the radiative capture of non-relativistic particles into bound states, in unbroken perturbative non-Abelian theories. We find that the formation of bound states via emission of a gauge boson can be significant for a variety of dark matter models that feature non-Abelian long-range interactions, including multi-TeV scale WIMPs, dark matter co-annihilating with coloured partners and hidden-sector models. Our results disagree with previous computations, on the relative sign of the Abelian and non-Abelian contributions. In particular, in the case of capture of a particle-antiparticle pair into its tightest bound state, we find that these contributions add up, rather than partially canceling each other. We apply our results to dark matter co-annihilating with particles transforming in the (anti)fundamental of SU(3)c, as is the case in degenerate stop-neutralino scenarios in the MSSM. We show that the radiative formation and decay of particle-antiparticle bound states can deplete the dark matter density by (40 − 240)%, for dark matter heavier than 500 GeV. This implies a larger mass difference between the co-annihilating particles, and allows for the dark matter to be as heavy as 3.3 TeV.