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Johan Rathsman

Publications and source records attributed to Johan Rathsman.

At least 19 recordsLinked to original sources
arXiv2026

Cosmological Signatures of the Conformal and Non-Conformal Next-to-Minimal Two-Higgs-Doublet Model

We investigate cosmological signatures of the next-to-minimal two-Higgs-doublet model (N2HDM) in both the classically scale-invariant, or conformal, realization and in the corresponding non-conformal theory. Using a one-loop finite-temperature effective potential, collider and flavour constraints implemented through ScannerS, HiggsBounds and HiggsSignals, and a modified on-shell counterterm prescription for the conformal model, we identify parameter regions with a first-order electroweak phase transition and potentially observable stochastic gravitational waves. We find that both conformal and non-conformal scenarios can produce sound-wave signals in the sensitivity range of future space-based interferometers, including LISA, while the electroweak transitions complete promptly ($T_n\simeq T_p$), with pronounced supercooling below the critical temperature confined to the strongest transitions. The two scenarios nevertheless populate different regions of the scalar mass spectrum when the gravitational-wave signal is observable, suggesting that a future stochastic background measurement combined with collider information on the additional Higgs states could discriminate between the two realizations. We further study partonic Higgs-pair production, in the heavy-top approximation, and find that large deviations in the SM-like di-Higgs rate tend to occur away from the regions with the strongest gravitational-wave signals, while enhanced BSM Higgs-pair rates are mainly associated with the conformal model. The analysis highlights a complementary interplay between electroweak cosmology, scalar spectroscopy and Higgs self-interaction probes in extended Higgs sectors.

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arXiv2026

The X17 Existence Hinted at by Nuclear Reactor Neutrinos

We show that by exploiting the process of Coherent Elastic neutrino (v) Nucleus Scattering (CEvNS), neutrino measurements by nuclear reactor experiments appear to corroborate the evidence of the so-called X17 particle, which has been invoked to explain the ATOMKI anomaly. We base our analysis primarily on CONUS+ and Dresden-II data, which, when combined with CEvNS data from COHERENT and neutrino oscillation data from IceCube, single out a unique region of couplings to neutrinos and nuclei.

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arXiv2026

Glimpses of the X17 from coherent elastic neutrino nucleus scattering

We show that the process of Coherent Elastic neutrino ({\nu}) Nucleus Scattering (CE{\nu}NS) at nuclear reactor experiments has significant sensitivity to the so-called X17 particle, which has been invoked to explain the ATOMKI anomaly, wherein electron-positron pairs emerging from a nuclear transition of excited Be-8, He-4 and C-12 nuclei are studied. Such a new state has potentially been identified as a spin-1 object, with axial-vector couplings and a mass around 16.7 MeV, hence, in the kinematic range accessible by the aforementioned experimental settings. Specifically, we fit CONUS+ and Dresden-II data and show that a robust statistical analysis renders these more compatible with the X17 hypothesis, in turn interfering with the Standard Model (SM), than with that of the latter alone. The same stays true when also adding COHERENT data from {\pi}+ decays at rest, singling out two regions of preferred couplings of the X17 to electron and muon neutrinos as well as nuclei.

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arXiv2025

Hunting the elusive $X17$ in CE$\nu$NS at the ESS

The so-called $X17$ particle has been proposed in order to explain a very significant resonant behaviour (in both the angular separation and invariant mass) of $e^+e^-$ pairs produced during a nuclear transition of excited $^8$Be, $^4$He and $^{12}$C nuclei. Fits to the corresponding data point, as most probable explanation, to a spin-1 object, which is protophobic and has a mass of approximately 16.7 MeV, which then makes the $X17$ potentially observable in Coherent Elastic neutrino ($\nu$) Nucleus Scattering (CE$\nu$NS) at the European Spallation Source (ESS). By adopting as theoretical framework a minimal extension of the Standard Model (SM) with a generic $U(1)'$ gauge group mixing with the hypercharge one of the latter, which can naturally accommodate the $X17$ state compliant with all available measurements from a variety of experiments, we predict that CE$\nu$NS at the ESS will constitute an effective means to probe this hypothesis, even after allowing for the inevitable systematics associated to the performance of the planned detectors therein.

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arXiv2025

Gravitational waves from color restoration in a leptoquark model of radiative neutrino masses

We study the first-order phase transitions and the emerging stochastic gravitational wave spectrum in a minimal leptoquark extension of the Standard Model that explains active neutrino oscillation data while satisfying current flavor physics constraints. This model exhibits diverse phase transition patterns, including color symmetry-breaking scenarios in the early Universe. Strong correlations between model parameters and gravitational-wave signals yield testable predictions for future experiments such as LISA, BBO, and DECIGO. Specifically, a detectable signal in the mHz$\unicode{x2013}$0.1~Hz frequency range features color-restoration and leptoquark masses near $1.5~\mathrm{TeV}$. With this article, we also present the first application in the literature of \texttt{Dratopi}. This is a soon-to-be-released tool for phase transition analysis using the dimensional reduction formalism, that interfaces the \texttt{DRalgo} package with \texttt{Python} and a slightly modified version of \texttt{CosmoTransitions}.

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arXiv2023

UV-complete Gauged Anomaly-free U(1) Froggatt-Nielsen Model

We investigate the possibility of understanding all fermion masses and mixings within a gauged Froggatt-Nielsen framework. Continuing the work from [J. Rathsman and F. Tellander, Phys. Rev. D \textbf{100}, 055032 (2019)] we especially focus on a UV completion of this type of models. Independent of the UV completion, we construct an anomaly-free two Higgs doublet model with a gauged $U(1)_F$ flavor symmetry and three right-handed neutrinos explaining all observed masses and mixings in the fermion sector. We then investigate two different UV completions: one through fermions and one through scalars. The fermion completion has low lying Landau poles in the gague couplings while the scalar completion is viable up to the gravity scale.

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arXiv2019

2-loop RG evolution of CP-violating 2HDM

We use the recently developed code 2HDME to perform a 2-loop renormalization group analyzis of the CP violating Two-Higgs-doublet model (2HDM). Using parameter scans of several scenarios of Z2 symmetry breaking, we investigate the properties of 2HDMs under renormalization group evolution. Collider data constraints are implemented with HiggsBounds and HiggsSignals and we include all the important Barr-Zee diagram contributions to the electron's electric dipole moment to put limits on the CP violation that is allowed both in the scalar and the Yukawa sector. As a result, we see that the CP violation spreads easily across the sectors during renormalization group evolution when one breaks the Z2 symmetry in either sector, putting additional constraints on the CP violating parameters.

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arXiv2019

Anomaly-free Model Building with Algebraic Geometry

We present a method to find anomaly-free gauged Froggatt-Nielsen type models using results from algebraic geometry. These methods should be of general interest for model building beyond the Standard Model (SM) when rational charges are required. We consider models with a gauged $U(1)$ flavor symmetry with one flavon and two Higgs doublets and three right-handed SM singlets to provide three model examples based on different physical assumptions. The models we study are: anomaly-free with no SM neutral heavy chiral fermions, anomaly-free with SM neutral heavy chiral fermions, and supersymmetric with SM neutral heavy chiral fermions where the anomalies cancel via the Green-Schwarz mechanism. With these different models we show how algebraic methods may be used in model building; both to reduce the charge constraints by calculation of Gr\"obner bases, and to find rational solutions to cubic equations using Mordell-Weil generators. Using these tools we find three phenomenologically viable models explaining the observed flavor structure.

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arXiv2019

Complementary bound on $W^\prime$ mass from Higgs to diphoton decay

Using the left-right symmetric model as an illustrative example, we suggest a simple and straightforward way of constraining the $W'$ mass directly from the decay of the Higgs boson to two photons. The proposed method is generic and applicable to a diverse range of models with a $W'$-boson that couples to the SM-like Higgs boson. Our analysis exemplifies how the precision measurement of the Higgs to diphoton signal strength can have a pivotal role in probing the scale of new physics.

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arXiv2018

Scalar Kinetic Mixing and the Renormalization Group

Quantum field theories containing scalar fields with equal quantum numbers allow for a mixed kinetic term in the Lagrangian. It has been argued that this mixing must be taken into consideration when performing renormalization group (RG) analyses of such a theory. However, from the fact that scalar kinetic mixing does not correspond to a physical observable, we show that no extra parameters need to be introduced. Using a toy model, we explicitly derive the 1-loop RG equations (RGEs) in three different renormalization schemes to demonstrate how this issue can be dealt with. In schemes without kinetic mixing, either the fields mix during renormalization to produce non-diagonal anomalous dimensions or the RGEs explicitly depend on the scalar masses. Finally, we show how the different schemes are related to each other by scale dependent field redefinitions.

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arXiv2018

$Z_2$ breaking effects in 2-loop RG evolution of 2HDM

We investigate the effects of a $Z_2$ symmetry in the CP-conserving Two-Higgs-Doublet-Model (2HDM); which is often imposed to prevent Flavor-Changing-Neutral-Currents (FCNCs) at tree-level. Specifically, we analyze how a breaking of the $Z_2$ symmetry spreads during renormalization group evolution; employing general 2-loop renormalization group equations that we have derived. Evolving the model from the electroweak to the Planck scale, we find that while the case of an exact $Z_2$ symmetric 2HDM is very constrained, a soft breaking of the $Z_2$ symmetry extends the valid parameter space regions. The effects of a hard $Z_2$ breaking in the scalar sector as well as the stability of the flavor alignment ansatz are also investigated. We find that while a hard breaking of the $Z_2$ symmetry in the potential is problematic, since it speeds up the growth of quartic couplings, the generated FCNCs are heavily suppressed. Conversely, we also find that hard $Z_2$ breaking in the Yukawa sector at most gives moderate $Z_2$ breaking in the potential; whereas the FCNCs can become quite sizable far away from the $Z_2$ symmetric regions.

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arXiv2013

Higgs phenomenology in the Stealth Doublet Model

We analyze a model for the Higgs sector with two scalar doublets and a $Z_2$ symmetry that is manifest in the Yukawa sector but broken in the potential. Thus, one of the doublets breaks the electroweak symmetry and has tree-level Yukawa couplings to fermions, whereas the other doublet has no vacuum expectation value and no tree-level couplings to fermions. Since the $Z_2$ parity is broken the two doublets can mix, which leads to a distinct and novel phenomenology. This Stealth Doublet Model can be seen as a generalization of the Inert Doublet Model with a broken $Z_2$ symmetry. We outline the model and present constraints from theory, electroweak precision tests and collider searches, including the recent observation of a Higgs boson at the LHC. The charged scalar $H^\pm$ and the CP-odd scalar $A$ couple to fermions at one-loop level. We compute the decays of $H^\pm$ and $A$ and in particular the one-loop decays $A \to f \bar{f}$, $H^\pm \to f \bar{f}^\prime $, $H^\pm \to W^\pm Z $ and $H^\pm \to W^\pm \gamma$. We also describe how to calculate and renormalize such processes in our model. We find that if one of $H^\pm$ or $A$ is the lightest scalar, $H^\pm \to W^\pm \gamma$ or $ A \to b \bar{b} $ are typically their respective dominating decay channels. Otherwise, the dominating decays of $H^\pm$ and $A$ are into a scalar and a vector. Due to the absence of tree-level fermion couplings for $H^\pm$ and $A$, we consider pair production and associated production with vector bosons and scalars at the LHC. If the parameter space of the model that favors $H^\pm \to W^\pm \gamma$ is realized in Nature, we estimate that there could be a considerable amount of such events in the present LHC data.

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arXiv2013

Higgs properties in a broken Inert Doublet Model

We consider a model for the Higgs sector with two scalar doublets and a broken $Z_2$ symmetry, the Stealth Doublet Model, where the $Z_2$ symmetry is manifest in the Yukawa sector but broken by the scalar potential. This model can be seen as a generalization of the Inert Doublet Model. One of the doublets is the Higgs doublet that participates in electroweak symmetry breaking and couples to fermions. The other doublet does not couple to fermions at tree level and does not acquire a vacuum expectation value. The broken $Z_2$ symmetry leads to interesting phenomenology such as mixing between the two doublets and charged and CP-odd scalars that can be light and have unusual decay channels. We present theoretical and experimental constraints on the model and consider the recent observation of a Higgs boson at the LHC. The data on the $H\to\gamma\gamma$ channel can be naturally accommodated in the model, with either the lightest or the heaviest CP-even scalar playing the role of the observed particle.

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arXiv2013

Constraining General 2HDM by the Evolution of Yukawa Couplings

We analysis the constraints of the general two Higgs doublet models via evolving the Yukawa coupling constants to high energy under renormalization group. We consider the appearance of a Landau pole or large off-diagonal Yukawa couplings which cause tree level flavour changing neutral currents. Our study shows the latter condition can be used to answer that how much $Z_2$ symmetry breaking can be allowed in a given 2HDM model.

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arXiv2012

Diffractive W production at hadron colliders as a test of colour singlet exchange mechanisms

We revisit diffractive and exclusive W production at hadron colliders in different models for soft colour exchanges. The process pp to p[WX]p, and in particular a W charge asymmetry, has been suggested as a way to discriminate diffractive processes as being due to pomeron exchange in Regge phenomenology or QCD-based colour reconnection models. Our detailed analysis of the latter models at LHC energies shows, however, that they give similar results as pomeron models for very leading protons and central W production, including a vanishing W charge asymmetry. We demonstrate that soft colour exchange models provide a continuous transition from diffractive to inelastic processes and thereby include the intrinsic asymmetry of inelastic interactions while being at the same time sensitive to the underlying hadronisation models. Such sensitivity also concerns the differential distributions in proton momentum and W transverse momentum which opens possibilities to discriminate between different colour reconnection models.

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arXiv2012

Closing the Window on Light Charged Higgs Bosons in the NMSSM

In the Next-to-Minimal SuperSymmetric Model (NMSSM) the lightest CP-odd Higgs bosons (a1) can be very light. As a consequence, in addition to the standard charged Higgs boson (h+) decays considered in the MSSM for a light charged Higgs (m_h+ < m_t), the branching fraction for h+ to a1 W can be dominant. We investigate how this signal can be searched for in t tbar production at the Large Hadron Collider (LHC) in the case that m_a1 \gtrsim 2m_B with the a1 giving rise to a single b bbar-jet and discuss to what extent the LHC experiments are able to discover such a scenario with an integrated luminosity \sim 20 fb-1. We also discuss the implications of the possible Higgs-signal observed at the LHC.

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arXiv2011

Constraining General Two Higgs Doublet Models by the Evolution of Yukawa Couplings

We study how general two Higgs doublet models can be constrained by considering their properties under renormalization group evolution of the Yukawa couplings. We take into account both the appearance of a Landau pole as well as off-diagonal Yukawa couplings leading to flavour changing neutral currents in violation with experimental constraints at the electroweak scale. We find that the latter condition can be used to limit the amount of Z2 symmetry breaking allowed in a given model.

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