arXiv subjects

J. M. No

Publications and source records attributed to J. M. No.

31 records · Page 2Linked to original sources

arXiv2017

Resonant Di-Higgs Production in the $b{\bar b}WW$ Channel: Probing the Electroweak Phase Transition at the LHC

We analyze the prospects for resonant di-Higgs production searches at the LHC in the $b\bar{b} W^+ W^-$ ($W^{+} \to \ell^{+} ν_{\ell}$, $W^{-} \to \ell^{-} \barν_{\ell}$) channel, as a probe of the nature of the electroweak phase transition in Higgs portal extensions of the Standard Model. In order to maximize the sensitivity in this final state, we develop a new algorithm for the reconstruction of the $b \bar{b} W^+ W^-$ invariant mass in the presence of neutrinos from the $W$ decays, building from a technique developed for the reconstruction of resonances decaying to $τ^{+}τ^{-}$ pairs. We show that resonant di-Higgs production in the $b\bar{b} W^+ W^-$ channel could be a competitive probe of the electroweak phase transition already with the datasets to be collected by the CMS and ATLAS experiments in Run-2 of the LHC. The increase in sensitivity with larger amounts of data accumulated during the High Luminosity LHC phase can be sufficient to enable a potential discovery of the resonant di-Higgs production in this channel.

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arXiv2016

A Second Higgs Doublet in the Early Universe: Baryogenesis and Gravitational Waves

We show that simple Two Higgs Doublet models still provide a viable explanation for the matter-antimatter asymmetry of the Universe via electroweak baryogenesis, even after taking into account the recent order-of-magnitude improvement on the electron-EDM experimental bound by the ACME Collaboration. Moreover we show that, in the region of parameter space where baryogenesis is possible, the gravitational wave spectrum generated at the end of the electroweak phase transition is within the sensitivity reach of the future space-based interferometer LISA.

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arXiv2016

Les Houches 2015: Physics at TeV colliders - new physics working group report

We present the activities of the 'New Physics' working group for the 'Physics at TeV Colliders' workshop (Les Houches, France, 1-19 June, 2015). Our report includes new physics studies connected with the Higgs boson and its properties, direct search strategies, reinterpretation of the LHC results in the building of viable models and new computational tool developments. Important signatures for searches for natural new physics at the LHC and new assessments of the interplay between direct dark matter searches and the LHC are also considered.

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arXiv2016

Non-linear Higgs portal to Dark Matter

The Higgs portal to scalar Dark Matter is considered in the context of non-linearly realised electroweak symmetry breaking. We determine the dominant interactions of gauge bosons and the physical Higgs particle $h$ to a scalar singlet dark matter candidate. Phenomenological consequences are also studied in detail, including the possibility of distinguishing this scenario from the standard Higgs portal in which the electroweak symmetry breaking is linearly realised. Two features of significant impact are: i) the connection between the electroweak scale $v$ and the Higgs particle departs from the $(v+h)$ functional dependence, as the Higgs field is not necessarily an exact electroweak doublet; ii) the presence of specific couplings that arise at different order in the non-linear and in the linear expansions. These facts deeply affect the dark matter relic abundance, as well as the expected signals in direct and indirect searches and collider phenomenology, where Dark Matter production rates are enhanced with respect to the standard portal.

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arXiv2016

Hierarchical vs Degenerate 2HDM: The LHC Run 1 Legacy at the Onset of Run 2

Current discussions of the allowed two-Higgs-doublet model (2HDM) parameter space after LHC Run 1 and the prospects for Run 2 are commonly phrased in the context of a quasi-degenerate spectrum for the new scalars. Here we discuss the generic situation of a 2HDM with a non-degenerate spectrum for the new scalars. This is highly motivated from a cosmological perspective since it naturally leads to a strongly first order electroweak phase transition that could explain the matter-antimatter asymmetry in the Universe. While constraints from measurements of Higgs signal strengths do not change, those from searches of new scalar states get modified dramatically once a non-degenerate spectrum is considered.

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arXiv2015

More Higgses at the LHC and the Electroweak Phase Transition

A cosmological first order electroweak phase transition could explain the origin of the cosmic matter-antimatter asymmetry. While it does not occur in the Standard Model, it becomes possible in the presence of a second Higgs doublet. In this context, we obtain the properties of the new scalars $H_0$, $A_0$ and $H^{\pm}$ leading to such a phase transition, showing that its key LHC signature would be the decay $A_0 \rightarrow H_0 Z$, and we analyze the promising LHC search prospects for this decay in the $\ell \ell b\bar{b}$ and $\ell \ell W^{+} W^{-}$ final states. Finally, we comment on the impact of the $A_0 \rightarrow H_0 Z$ decay on current LHC searches for $A_0$ decaying into SM particles.

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arXiv2014

Echoes of the Electroweak Phase Transition: Discovering a second Higgs doublet through $A_0 \rightarrow H_0 Z$

The existence of a second Higgs doublet in Nature could lead to a cosmological first order electroweak phase transition and explain the origin of the matter-antimatter asymmetry in the Universe. We obtain the spectrum and properties of the new scalars $H_0$, $A_0$ and $H^{\pm}$ that signal such a phase transition, and show that the observation of the decay $A_0 \rightarrow H_0 Z$ at LHC would be a `smoking gun' signature of these scenarios. We analyze the LHC search prospects for this decay in the $\ell \ell b\bar{b}$ and $\ell \ell W^{+} W^{-}$ final states, arguing that current data may be sensitive to this signature in the former channel as well as there being great potential for a discovery in either one at the very early stages of the 14 TeV run.

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arXiv2013

A strong electroweak phase transition in the 2HDM after LHC8

The nature of the electroweak phase transition in two-Higgs-doublet models is revisited in light of the recent LHC results. A scan over an extensive region of their parameter space is performed, showing that a strongly first-order phase transition favours a light neutral scalar with SM-like properties, together with a heavy pseudo-scalar (m_A^0 > 400 GeV) and a mass hierarchy in the scalar sector, m_H^+ < m_H^0 < m_A^0. We also investigate the h^0 -> gamma gamma decay channel and find that an enhancement in the branching ratio is allowed, and in some cases even preferred, when a strongly first-order phase transition is required.

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arXiv2009

Some Cosmological Implications of Hidden Sectors

We discuss some cosmological implications of extensions of the Standard Model with hidden sector scalars coupled to the Higgs boson. We put special emphasis on the conformal case, in which the electroweak symmetry is broken radiatively with a Higgs mass above the experimental limit. Our refined analysis of the electroweak phase transition in this kind of models strengthens the prediction of a strongly first-order phase transition as required by electroweak baryogenesis. We further study gravitational wave production and the possibility of low-scale inflation as well as a viable dark matter candidate.

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arXiv2008

A Note on Unparticle Decays

The coupling of an unparticle operator O_U to Standard Model particles opens up the possibility of unparticle decays into standard model fields. We study this issue by analyzing the pole structure (and spectral function) of the unparticle propagator, corrected to account for one-loop polarization effects from virtual SM particles. We find that the propagator of a scalar unparticle (of scaling dimension 1 < d_U < 2) with a mass gap m_g develops an isolated pole, m_p^2-i m_p Gamma_p, with m_p^2 < m_g^2 below the unparticle continuum that extends above m_g (showing that the theory would be unstable without a mass gap). If that pole lies below the threshold for decay into two standard model particles the pole corresponds to a stable unparticle state (and its width Gamma_p is zero). For m_p^2 above threshold the width is non zero and related to the unparticle decay rate into Standard Model particles. This picture is valid for any value of d_U in the considered range.

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arXiv2008

Phantom Higgs from Unparticles

A renormalizable coupling between the Higgs and a scalar unparticle operator O_U of non-integer dimension d_U < 2 gives rise, after electroweak symmetry breaking, to a mass gap in the unparticle continuum and a shift in the original Higgs mass, which can end up above or below the mass gap. We show that, besides the displaced Higgs state, a new isolated state can generically appear in the spectrum near or below the mass gap. Such state (which we call phantom Higgs) is a mixture of Higgs and unparticles and therefore has universally reduced couplings to fermions and gauge bosons. This phenomenon could cause the mass of the lightest Higgs state accessible to colliders to be much smaller than the mass expected from the SM Lagrangian.

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arXiv2008

The Higgs as a Portal to Plasmon-like Unparticle Excitations

A renormalizable coupling between the Higgs and a scalar unparticle operator O_U of non-integer dimension d_U<2 triggers, after electroweak symmetry breaking, an infrared divergent vacuum expectation value for O_U. Such IR divergence should be tamed before any phenomenological implications of the Higgs-unparticle interplay can be drawn. In this paper we present a novel mechanism to cure that IR divergence through (scale-invariant) unparticle self-interactions, which has properties qualitatively different from the mechanism considered previously. Besides finding a mass gap in the unparticle continuum we also find an unparticle pole reminiscent of a plasmon resonance. Such unparticle features could be explored experimentally through their mixing with the Higgs boson.

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arXiv2006

Scalar Loops in Little Higgs Models

Loops of the scalar particles present in Little Higgs models generate radiatively scalar operators that have been overlooked before in Little Higgs analyses. We compute them using a technique, recently proposed to deal with scalar fluctuations in non-linear sigma models, that greatly simplifies the calculation. In particular models some of these operators are not induced by loops of gauge bosons or fermions, are consistent with the Little Higgs symmetries that protect the Higgs boson mass, and must also be included in the Lagrangian. In general, scalar loops multiplicatively renormalize the tree-level scalar operators, O_S -> O_S [1- N Λ^2/(4πf)^2] with large N (e.g. N ~ 20 for the Littlest Higgs), suggesting a true UV cutoff Λ< 4 πf/\sqrt{N} significantly below the estimate 4πf of naive dimensional analysis. This can have important implications for the phenomenology and viability of Little Higgs models.

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