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Guglielmo Coloretti

Publications and source records attributed to Guglielmo Coloretti.

17 recordsLinked to original sources
arXiv2026

Searching for charged Higgs bosons in top decays via the $t^*b$ channel

Rare top-quark decays offer a sensitive probe of charged Higgs bosons with masses below the top mass, owing to the large $t\bar t$ production rate at the LHC and the distinctive final states involving leptons and $b$-jets. While existing searches target the $H^\pm\to \tau\nu$, $cs$, and $cb$ modes, the decay $H^\pm\to tb$ has been studied only for heavier charged Higgs bosons with an on-shell top quark in the final state. The low-mass off-shell channel $H^\pm\to t^*b$ therefore remains essentially unconstrained, even though it can become the dominant decay mode below the top-quark threshold owing to the large top Yukawa coupling. We study charged-Higgs production from the rare top decay $t\to H^\pm b$, followed by the decay $H^\pm\to t^*b$. Top-antitop production and decay hence give rise to a $t\bar t b\bar b$-like final state, which we constrain by reinterpreting recent ATLAS fiducial measurements in dileptonic events. We obtain model-independent limits of 1.9%-2.9% on the product of branching ratios ${\rm Br}(t\to H^\pm b)\times{\rm Br}(H^\pm\to t^*b)$ for charged-Higgs masses between 110 and 165 GeV, and interpret these bounds in several two-Higgs-doublet scenarios. While dedicated searches for conventional charged-Higgs decays dominate for canonical $Z_2$-symmetric models, the $t^*b$ reinterpretation becomes competitive near the top-quark threshold in the up-type aligned limit and provides relevant direct constraint in a top-philic scenario. In the top-specific Two-Higgs-Doublet Model, it additionally excludes a low-$\tan\beta$ region not covered by conventional searches. These results thus establish $t\bar t$ production with additional $b$-jets as a complementary probe of light charged Higgs bosons and nonstandard top-quark decays, and motivate dedicated analyses by the LHC collaborations.

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arXiv2026

Indications for New Higgs Bosons

After the Higgs discovery, the question of whether particles beyond those of the Standard Model exist is more pressing than ever. In this context, the scalar sector is particularly promising, since it lies at the core of the internal problems of the Standard Model, while extensions of it allow us to resolve them and can provide explanations for Dark matter, non-zero neutrino masses, inflation etc. In these proceedings, we review the indications for new Higgs bosons at the electroweak scale with masses of $\approx$95 GeV and $\approx$152 GeV. These excesses are most significant in the di-photon channel but are supported by weaker-than-expected limits in other decay modes. While for the 95 GeV candidate the production mechanism is mostly unknown, the (hypothetical) 152 GeV Higgs is dominantly produced in association with leptons, $(b)$ jets and missing energy, pointing towards the Drell-Yan production of an $SU(2)_L$ triplet with $Y=0$. Interestingly, this model predicts $t\to H^\pm b$ with $H^\pm\to WZ$, which resembles the signature of $t\bar{t}Z$ production in the Standard Model and is in fact preferred by current data. Finally, we investigate the possibility that the significant tensions between the Standard Model predictions and the measurements in differential top-quark distributions are due to contamination from new physics involving both the 152 GeV and the 95 GeV scalar.

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arXiv2025

Correlating Resonant Di-Higgs and Tri-Higgs Production to $H\to VV$ in the 2HDM

The observation of resonant di-Higgs production, which would strongly suggest the existence of a new heavy neutral scalar $H$, has been searched for extensively at the LHC. In the two-Higgs doublet model (2HDM) with $m_H\gg m_h$, where $h$ is the Higgs boson of mass 125 GeV observed at the LHC, we show that a direct correlation emerges between ${\rm Br}(H\to hh)$ and ${\rm Br}(H\to VV)$, with $V=Z,W$, which depends only on $m_H$ (and $m_V$). In particular, for heavy scalar masses between 500 GeV and 1 TeV, we find that ${\rm Br}(H\to hh)/{\rm Br}(H\to ZZ)\approx 9.4\pm 0.25$. Moreover, $H\to hh$ is a dominant decay mode over a significant region of the parameter space and serves as the primary probe for a heavy scalar resonance at current and future hadron colliders. The origin of these predictions is most transparent in the Higgs basis, where the term in the scalar potential proportional to $\mathcal H_1^\dagger \mathcal H_1 \mathcal H_1^\dagger \mathcal H_2$ (and its hermitian conjugate) generates the leading contributions to the $Hhh$ and $Hhhh$ couplings in the decoupling limit of the 2HDM. Additionally, the latter coupling governs the resonant prompt tri-Higgs production via $H\to hhh$, which is also directly correlated to $H\to hh$ (and $H\to VV$), and can yield rates large enough to be measured at the High-Luminosity LHC.

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arXiv2025

Constraining $A\to ZH$ with $H\to t\bar t$ in the Low-Mass Region

The decay $A\to ZH$ is a characteristic signal of two-Higgs-doublet models (2HDMs), where $A$ and $H$ lie primarily within the same $SU(2)_L$ multiplet, leading to a coupling of order $g_2$ to the $Z$ boson. The subsequent decay $H\to tt^{(*)}$ is particularly promising, as it gives rise to distinct final states involving multiple leptons and $b$-jets. The required splitting between $m_A$ and $m_H$ can naturally occur near the electroweak scale while being consistent with perturbative unitarity. Whereas dedicated ATLAS and CMS searches focused on the region with both top-quarks on-shell, we cover lower masses where one top quark is off-shell by recasting Standard Model $t\bar{t}Z$ measurements of ATLAS and CMS. The obtained limits on $\sigma(A\to ZH)\times {\rm Br} (H\to t\bar t)$ are between $0.12$ pb and $0.62$ pb. Interestingly, we observe these stringent limits despite a preference (up to $2.5\sigma$) for a non-zero new physics signal, most pronounced around for $m_A \approx 450-460$ GeV and $m_H\approx 290$ GeV, with a best-fit value of $\sigma(A \to ZH) \times {\rm Br}(H \to t\bar t) \approx 0.3$ pb. This cross section can be accommodated within a top-philic 2HDM for a top-Yukawa coupling of the second Higgs doublet of $\mu_t \gtrsim 0.16$.

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arXiv2025

Searching for Di-Higgs Signatures of Light Charged Scalars

The excess in $t\to b\overline{b}c$ observed by ATLAS points towards a charged Higgs boson with a mass around 130$\,$GeV, consistent with the expectations from the $B$ anomalies, i.e.$~R_{D^{(*)}}$ and $b\to s\ell^+\ell^-$ data. As a non-minimal flavour structure is required for an explanation of these observables, this points towards a two-Higgs-doublet model with generic Yukawa couplings. Such a scenario predicts a sizable cross section for the pair production of the charged Higgs at the Large Hadron Collider, which can be tested by recasting SM di-Higgs searches. While the predicted event rate is even higher than the one of SM Higgs pair production, the smaller efficiency (w.r.t.$~$SM Higgs pair production) reduces the signal yield. Nonetheless, dedicated searches can probe most of the interesting parameter space and lead to a discovery with Run-3 or High-Luminosity LHC data.

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arXiv2025

Entanglement Maximization and Mirror Symmetry in Two-Higgs-Doublet Models

We consider 2-to-2 scatterings of Higgs bosons in a CP-conserving two-Higgs-doublet model (2HDM) and study the implication of maximizing the entanglement in the flavor space, where the two doublets $\Phi_a$, $a=1,2$, can be viewed as a qubit: $\Phi_1=|0\rangle$ and $\Phi_2=|1\rangle$. More specifically, we compute the scattering amplitudes for $\Phi_a \Phi_b \to \Phi_c \Phi_d$ and require the outgoing flavor entanglement to be maximal for a full product basis such as the computational basis, which consists of $\{|00\rangle,|01\rangle,|10\rangle,|11\rangle\}$. In the unbroken phase and turning off the gauge interactions, entanglement maximization results in the appearance of an $U(2)\times U(2)$ global symmetry among the quartic couplings, which in general is broken softly by the mass terms. Interestingly, once the Higgs bosons acquire vacuum expectation values, maximal entanglement enforces an exact $U(2) \times U(2)$ symmetry, which is spontaneously broken to $U(1)\times U(1)$. As a byproduct, this gives rise to Higgs alignment as well as to the existence of 6 massless Nambu-Goldstone bosons. The $U(2)\times U(2)$ symmetry can be gauged to lift the massless Goldstones, while maintaining maximal entanglement demands the presence of a discrete $\mathrm{Z}_2$ symmetry interchanging the two gauge sectors. The model is custodially invariant in the scalar sector, and the inclusion of fermions requires a mirror dark sector, related to the standard one by the $\mathrm{Z}_2$ symmetry.

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arXiv2024

Correlating $A \to \gamma\gamma$ with electric dipole moments in the two Higgs doublet model in light of the diphoton excesses at 95 GeV and 152 GeV

We examine the correlations between new scalar boson decays to photons and electric dipole moments (EDMs) in the CP-violating flavor-aligned two-Higgs-doublet model (2HDM). It is convenient to work in the Higgs basis $\{{H}_1, {H}_2\}$ where only the first Higgs doublet field ${H}_1$ acquires a vacuum expectation value. In light of the LHC Higgs data, which agree well with Standard Model (SM) predictions, it follows that the parameters of the 2HDM are consistent with the Higgs alignment limit. In this parameter regime, the observed SM-like Higgs boson resides almost entirely in ${H}_1$, and the other two physical neutral scalars, which reside almost entirely in ${H}_2$, are approximate eigenstates of CP (denoted by the CP-even $H$ and the CP-odd $A$). In the Higgs basis, the scalar potential term $\bar{Z}_7 {H}_1^\dagger {H}_2 {H}_2^\dagger {H}_2+{\rm h.c.}$ governs the charged-Higgs loop contributions to the decay of $H$ and $A$ to photons. If $ \text{Re } \bar{Z}_7 \, \text{Im } \bar{Z}_7 \neq 0$, then CP-violating effects are present and allow for an $H^+ H^- A$ coupling, which can yield a sizable branching ratio for $A\to\gamma\gamma$. These CP-violating effects also generate non-zero EDMs for the electron, the neutron and the proton. We examine these correlations for the cases of $m_{A}=95$ GeV and $m_{A}=152$ GeV where interesting excesses in the diphoton spectrum have been observed at the LHC. These excesses can be explained via the decay of $A$ while being consistent with the experimental bound for the electron EDM in regions of parameter space that can be tested with future neutron and proton EDM measurements. This allows for the interesting possibility where the 95 GeV diphoton excess can be identified with $A$, while $m_H\simeq 98$ GeV can account for the best fit to the LEP excess in $e^+e^-\to ZH$ with $H\to b\bar b$.

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arXiv2024

Anatomy of the Real Higgs Triplet Model

In this article, we examine the Standard Model extended by a $Y=0$ real Higgs triplet, the $\Delta$SM. It contains a $CP$-even neutral Higgs ($\Delta^0$) and two charged Higgs bosons ($\Delta^\pm$), which are quasi-degenerate in mass. We first study the theoretical constraints from vacuum stability and perturbative unitarity and then calculate the Higgs decays, including the loop-induced modes such as di-photons ($\gamma\gamma$) and $Z\gamma$. In the limit of a small mixing between the SM Higgs and $\Delta^0$, the latter decays dominantly to $WW$ and can have a sizable branching ratio to di-photon. The model predicts a positive definite shift in the $W$ mass, which agrees with the current global electroweak fit. At the Large Hadron Collider, it leads to a $(i)$ stau-like signature from $pp\to \Delta^+\Delta^-\to \tau^+\tau^-\nu\bar\nu$, $(ii)$ multi-lepton final states from $pp\to \gamma^*\to \Delta^+\Delta^-\to W^+W^-ZZ$ and $pp\to W^{*} \to \Delta^\pm\Delta^0\to W^\pm Z W^+W^-$ as well as $(iii)$ associated di-photon production from $pp\to W^{*} \to \Delta^\pm(\Delta^0\to\gamma\gamma)$. Concerning $(i)$, the reinterpretation of the recent supersymmetric tau partner search by ATLAS and CMS excludes $m_{\Delta^\pm}<110$ GeV at 95% CL. From $(ii)$, some of the signal regions of multi-lepton searches lead to bounds close to the predicted cross-section, but electroweak scale masses are still allowed. For $(iii)$, the recast of the associated di-photon searches by ATLAS and a combined log-likelihood fit of signal and background to data find that out of the 25 signal regions, 10 provide relevant limits on Br$(\Delta^0\to\gamma\gamma)$ at the per cent level. Interestingly, 6 signal regions show excesses at around 152 GeV, leading to a preference for a non-zero di-photon branching ratio of about 0.7% with the corresponding significance amounting to about $4\sigma$.

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arXiv2024

Growing Evidence for a Higgs Triplet

Despite intensive searches at the LHC, no new fundamental particle has been discovered since the discovery of the 125 GeV Higgs boson. In general, a new physics discovery is challenging without a UV-complete model because different channels and observables cannot be combined directly and unambiguously. Moreover, without indirect hints for new particles, the parameter space to be searched is huge, resulting in diminished significance due to the look-elsewhere effect. Several LHC searches with multiple leptons in the final state point towards the existence of a new Higgs boson with a mass in the 140-160 GeV range, decaying mostly to a pair of W bosons. This dominant decay mode motivates a Higgs triplet with zero hypercharge, which also predicts a heavier-than-expected $W$-boson as indicated by the CDF-II measurement. Within this simple and predictive model, we simulate and combine channels of associated di-photon production. Considering the run-2 results of ATLAS, including those presented recently at the Moriond conference, a significance of 4.3$\sigma$ is obtained for a mass of 152 GeV. This is the largest statistical evidence for a new narrow resonance observed at the LHC.

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arXiv2024

Explaining the $\gamma\gamma+X$ Excesses at $\approx$151.5 GeV via the Drell-Yan Production of a Higgs Triplet

The multi-lepton anomalies and searches for the associated production of a narrow resonance indicate the existence of a $\approx$151 GeV Higgs with a significance of $>5\sigma$ and $>3.9\sigma$, respectively. On the one hand, these anomalies require a sizable branching fraction of the new scalar to $WW$, while on the other hand, no $ZZ$ signal at this mass has been observed. This suggests that the new boson is the neutral component of an $SU(2)_L$ triplet with zero hypercharge. This field leads to a positive definite shift in the $W$ mass, as preferred by the current global fit, and is produced via the Drell-Yan process $pp\to W^*\to \Delta^0\Delta^\pm$. We use the side-bands of the ATLAS analysis \cite{ATLAS:2023omk} of the associated production of the Standard Model Higgs in the di-photon channel to search for this production mode of the triplet. Since the dominant decays of $\Delta^\pm$ depend only on its mass, the effect in the 22 signal categories considered by ATLAS is completely correlated. We find that the ones most sensitive to the Drell-Yan production of the triplet Higgs show consistent excesses at a mass of $\approx$151.5 GeV. Combining these channels in a likelihood ratio test, a non-zero Br$[\Delta^0\to\gamma\gamma] = 0.66\%$ is preferred by $\approx$3$\sigma$, supporting our conjecture.

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arXiv2023

Combined Explanation of LHC Multi-Lepton, Di-Photon and Top-Quark Excesses

The LHC analyses of processes containing two or more leptons and missing energy, possibly in association with b-jets, show strong tensions with the Standard Model predictions and are known as multi-lepton anomalies. In particular, top-quark differential distributions point towards the associated production of new Higgs bosons decaying into bottom quarks and W bosons ($>5\sigma$) with masses consistent with the di-photon excesses at 95GeV and 152GeV ($3.8\sigma$ and $4.9\sigma$, respectively). Furthermore, CMS found indications for resonant top-quark pair production at 400GeV ($3.5\sigma$) and both ATLAS and CMS reported elevated four-top and ttW cross-sections. In this article, we propose a combined explanation of these excesses by supplementing the SM Higgs with a second scalar doublet, a real scalar singlet ($S$) and a Higgs triplet with $Y=0$ ($\Delta$); the $\Delta$2HDMS. We fix the masses of the neutral triplet-like and the singlet-like scalars by the di-photon excesses, i.e. $m_{\Delta^0}=152$GeV and $m_S=95$GeV, respectively. Here, H, the CP-even component of the second doublet, is produced via gluon fusion from a top-loop and decays dominantly to $S+\Delta^0$ whose subsequent decays to WW and bb explain the differential top-quark distributions for $\sigma(pp\to H\to S\Delta^0)\approx6$pb. Fixing the top-Yukawa accordingly, the CP-odd Higgs boson A turns out to have the right production cross-section to account for the resonant top-pair excess at 400GeV, while the top-associated production of H and A results in new physics pollution of Standard Model ttW and four-top cross sections, as preferred by the data. Furthermore, a positive shift in the W mass is naturally induced by the vacuum expectation value of the triplet and we show that the most relevant signal strengths of the 152GeV boson are compatible with the process $pp\to H\to \Delta^0S$ if S is allowed to decay invisibly.

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arXiv2023

Differential $e\mu bb $ Cross-Sections and New Higgses at the Electroweak Scale

ATLAS found that none of their Standard Model simulations can describe the measured differential lepton distributions in their $t \bar{t}$ analysis reasonably well. Therefore, we study the possibility that this measurement has a new physics contamination. We consider a benchmark model motivated by the indications for di-photon resonances: A heavy scalar decays into two lighter Higgs bosons with masses of 152\,GeV and 95\,GeV, with subsequent decay to $WW$ and $bb$, respectively. In this setup, the description of data is improved by at least $5.6 \sigma$.

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arXiv2023

Uncovering New Higgses in the LHC Analyses of Differential $t\bar t$ Cross Sections

Statistically significant tensions between the Standard Model (SM) predictions and the measured lepton distributions in differential top cross-sections emerged in LHC Run~1 data and became even more pronounced in Run~2 analyses. Due to the level of sophistication of the SM predictions and the performance of the ATLAS and CMS detectors, this is very remarkable. Therefore, one should seriously consider the possibility that these measurements are contaminated by beyond-the-SM contributions. In this article, we use differential lepton distributions from the latest ATLAS $t\bar t$ analysis to study a new physics benchmark model motivated by existing indications for new Higgses: a new scalar $H$ is produced via gluon fusion and decays to $S^\prime$ ($95\,$GeV) and $S$ ($152\,$GeV), which subsequently decay to $b\bar b$ and $WW$, respectively. In this setup, the total $\chi^2$ is reduced, compared to the SM, resulting in $\Delta\chi^2=34$ to $\Delta\chi^2=158$, depending on the SM simulation used. Notably, allowing $m_S$ to vary, the combination of the distributions points towards $m_S\!\approx\!150\,$GeV which is consistent with the existing $\gamma \gamma$ and $WW$ signals, rendering a mismodelling of the SM unlikely. Averaging the results of the different SM predictions, a non-vanishing cross-section for $pp\to H\to SS^\prime\to b\bar b WW$ of $\approx\!13$pb is preferred. If $S^\prime$ is SM-like, this cross-section, at the same time explains the $95\,$GeV $\gamma\gamma$ excess, while the dominance of $S\to WW$ suggests that $S$ is the neutral component of the $SU(2)_L$ triplet with hypercharge~0.

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arXiv2023

Growing Excesses of New Scalars at the Electroweak Scale

We combine searches for scalar resonances at the electroweak scale performed by the Large Hadron Collider experiments ATLAS and CMS where persisted excesses have been observed in recent years. Using both the side-bands of Standard Model Higgs analyses as well as dedicated beyond the Standard Model analyses, we find significant hints for new scalars at $\approx 95\,$GeV ($S^\prime$) and $\approx152\,$GeV ($S$). The presence of a $95\,$GeV scalar is preferred over the Standard Model hypothesis by $3.8\sigma$, while interpreting the $152\,$GeV excesses in a simplified model with resonant pair production of $S$ via a new heavier scalar $H(270)$, a global significance of $\approx5\sigma$ is obtained. While the production mechanism of the $S^\prime$ cannot yet be determined, data strongly favours the associated production of $S$, i.e. via the decay of a heavier boson $H$ ($pp\to H\to SS^*$). A possible alternative or complementary decay chain is $H\rightarrow SS^{\prime}$, where $S\to WW^*$ ($S^{\prime}$) would be the source of the leptons ($b$-quarks) necessary to explain the multi-lepton anomalies found in Large Hadron Collider data.

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arXiv2023

$SU(2)_L$ triplet scalar as the origin of the 95 GeV excess?

We explore the possibility that an $SU(2)_L$ triplet scalar with hypercharge $Y=0$ is the origin of the $95\,$GeV diphoton excess. For a small mixing angle with the Standard Model Higgs, its neutral component has naturally a sizable branching ratio to $\gamma\gamma$ such that its Drell-Yan production via $pp\to W^*\to H H^\pm$ is sufficient to obtain the desired signal strength, where $H^\pm$ is the charged Higgs component of the triplet. The predictions of this setup are: 1) The $\gamma\gamma$ signal has a $p_T$ spectrum different from gluon fusion but similar to associated production. 2) Photons are produced in association with tau leptons and jets, but generally do not fall into the vector-boson fusion category. 3) The existence of a charged Higgs with $m_{H^\pm}\approx\!(95\pm5)\,$GeV leading to $\sigma(pp\to \tau\tau\nu\nu)\approx0.4\,$pb, which is of the same level as the current limit and can be discovered with Run 3 data. 4) A positive definite shift in the $W$ mass as suggested by the current global electroweak fit.

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arXiv2023

Searching for Low-Mass Resonances Decaying into $W$ Bosons

In this article, we recast and combine the CMS and ATLAS analyses of the Standard Model Higgs boson decaying to a pair of $W$ bosons in order to search for low-mass resonances in this channel. We provide limits on the corresponding cross section assuming direct production via gluon fusion. For the whole range of masses we consider (90$\,$GeV to 200$\,$GeV), the observed limit on the cross section turns out to be weaker than the expected one. Furthermore, at $\approx95\,$GeV the limit is weakest and a new scalar decaying into a pair of $W$ bosons (which subsequently decay leptonically) with a cross section $\approx0.5\,$pb is preferred over the Standard Model hypothesis by $\gtrsim 2.5\,\sigma$. In light of the excesses in the $\gamma\gamma$, $\tau^+\tau^-$ and $b\bar b$ channels at similar masses, this strengthens the case for such a new Higgs boson. Furthermore, this analysis also gives room for the scalar candidate at 151$\,$GeV decaying into $W$ bosons.

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arXiv2022

QCD Predictions for Event-Shape Distributions in Hadronic Higgs Decays

We study the six classical event-shape observables in hadronic Higgs decays at next-to-leading order in QCD. To this end, we consider the decay of on-shell Higgs bosons to three partons, taking into account both the Yukawa-induced decay to $\mathrm{b}$-quark pairs and the loop-induced decay to two gluons via an effective Higgs-gluon coupling. The results are discussed with a particular focus on the discriminative power of event shapes regarding these two classes of processes.

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