We update the phenomenology of gauge singlet extensions of the Standard Model scalar sector and their implications for the electroweak phase transition. Considering the introduction of one real scalar singlet to the scalar potential, we analyze present constraints on the potential parameters from Higgs coupling measurements at the Large Hadron Collider (LHC) and electroweak precision observables for the kinematic regime in which no new scalar decay modes arise. We then show how future precision measurements of Higgs boson signal strengths and Higgs self-coupling could probe the scalar potential parameter space associated with a strong first-order electroweak phase transition. We illustrate using benchmark precision for several future collider options, including the High Luminosity LHC (HL-LHC), the International Linear Collider (ILC), TLEP, China Electron Positron Collider (CEPC), and a 100 TeV proton-proton collider, such as the Very High Energy LHC (VHE-LHC) or the Super proton-proton Collider (SPPC). For the regions of parameter space leading to a strong first order electroweak phase transition, we find that there exists considerable potential for observable deviations from purely Standard Model Higgs properties at these prospective future colliders.

We study the prospects for probing a gauge singlet scalar-driven strong first order electroweak phase transition with a future proton-proton collider in the 100 TeV range. Singlet-Higgs mixing enables resonantly-enhanced di-Higgs production, potentially aiding discovery prospects. We perform Monte Carlo scans of the parameter space to identify regions associated with a strong first-order electroweak phase transition, analyze the corresponding di-Higgs signal, and select a set of benchmark points that span the range of di-Higgs signal strengths. For the bbγγ and 4τ final states, we investigate discovery prospects for each benchmark point for the high luminosity phase of the Large Hadron Collider and for a future pp collider with √ s = 50, 100, or 200 TeV. We find that any of these future collider scenarios could significantly extend the reach beyond that of the high luminosity LHC, and that with √ s = 100 TeV (200 TeV) and 30 ab −1 , the full region of parameter space favorable to strong first order electroweak phase transitions is almost fully (fully) discoverable.

We analyze the prospects for resonant di-Higgs production searches at the LHC in the bbW þ W − (W þ → l þ ν l , W − → l −ν l ) 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 bbW þ 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 þ τ − pairs. We show that resonant di-Higgs production in the bbW þ W − channel could be a competitive probe of the electroweak phase transition already with the data sets 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. I. MOTIVATIONWith the discovery of the Higgs boson at the Large Hadron Collider (LHC) [1,2], exploring the thermal history associated with electroweak symmetry breaking (EWSB) has taken on heightened interest. In the Standard Model (SM), EWSB in the early Universe occurs through a crossover transition. In contrast, beyond-the-StandardModel (BSM) scenarios may lead to a bona fide electroweak phase transition (EWPT). If such a transition occurred and was both first order and sufficiently strong, it could have provided the conditions needed for generating the observed cosmic matter-antimatter asymmetry.Electroweak baryogenesis (EWBG) (for recent reviews, see Refs. [3,4]) is one of the most widely studied and experimentally testable scenarios for explaining the origin of the cosmic matter-antimatter asymmetry, characterized by the baryon-to-entropy density ratio Y B ¼ n B =s as (most precisely) measured by Planck [5]:Successful baryogenesis requires three ingredients in the particle physics of the early Universe, the so-called "Sakharov criteria" [6]: (i) baryon-number (B) violation,(ii) C and CP violation, and (iii) departure from thermal equilibrium or a breakdown of CPT invariance. The SM contains the requisite B violation in the guise of electroweak sphalerons, but it fails with regard to the last two criteria. CP violation in the SM, via the CKM mixing matrix, is too feeble. In the minimal SM, the maximum Higgs mass for a first-order EWPT is m h ∼ 70-80 GeV, as confirmed by a variety of theoretical Monte Carlo simulations [7][8][9][10][11]; while for the observed m h ∼ 125 GeV, EWSB occurred through a crossover phase transition in the early Universe, which would not provide for the necessary out-of-equilibrium conditions. In contrast, if the observed Higgs boson resides within an extended scalar sector, the nature and properties of the EWPT could differ significantly from those of the SM. In that case, the Universe could have undergone a strong firstorder EWPT even for a SM-like Higgs boson of mass m h ∼ 125 GeV. The additional scalar degrees of freedom can...

We analyze the sensitivity of next-generation tonne-scale neutrinoless double-β decay (0νββ) experiments and searches for same-sign di-electrons plus jets at the Large Hadron Collider to TeV scale lepton number violating interactions. Taking into account previously unaccounted for physics and detector backgrounds at the LHC, renormalization group evolution, and long-range contributions to 0νββ nuclear matrix elements, we find that the reach of tonne-scale 0νββ generally exceeds that of the LHC for a class of simplified models. However, for a range of heavy particle masses near the TeV scale, the high luminosity LHC and tonne-scale 0νββ may provide complementary probes. DOI: 10.1103/PhysRevD.93.093002 Total lepton number (L) is a conserved quantum number at the classical level in the Standard Model (SM) of particle physics, yet it is not conserved in many scenarios for physics beyond the Standard Model (BSM). Experimentally, the observation of neutrinoless double-beta decay (0νββ decay) of atomic nuclei would provide direct evidence for lepton number violation (LNV 25 years. When interpreted in terms of the exchange of light Majorana neutrinos, these limits imply an upper bound of order 100-400 meV on the 0νββ-decay effective mass m ββ , depending on the value of the nuclear matrix element employed in this extraction [11]. The next generation of "tonne scale" 0νββ-decay searches aim for half-life sensitivities of order ∼10 27 years, with a corresponding m ββ sensitivity on the order of tens of meV, consistent with expectations based on the inverted hierarchy (IH) for the light neutrino mass spectrum. In this interpretive framework, a null result would imply that either neutrinos are Majorana particles with a mass spectrum in the normal hierarchy (NH) or that they are Dirac fermions.It is possible that neutrino oscillation studies may determine the neutrino mass hierarchy before the next generation 0νββ-decay searches reach their goal sensitivity. Should the hierarchy turn out to be normal, a null result from the tonne-scale 0νββ-decay experiments would not be surprising. However, alternate decay mechanisms could still lead to observation of a signal in the next generation searches, even if the light neutrino spectrum follows the NH and the value of m ββ is experimentally inaccessible. These mechanisms include radiative neutrino mass scenarios [12] and the TeV-scale seesaw mechanism [13][14][15][16][17][18][19] [20]. In these scenarios, the LNV interactions may involve particles whose masses are of order one TeV and whose exchange generates short range interactions that lead to 0νββ decay. Straightforward arguments indicate that the resulting 0νββ-decay half-life can be of order 10 27 yr or shorter, comparable to expectations based on the three light Majorana exchange mechanism and the IH [21]. The associated light Majorana masses may nevertheless follow the NH with m ββ well below the meV scale.How might one experimentally distinguish the TeV LNV scenario for 0νββ decay from the more conventional paradigm base...

We propose a scenario that generates the observed baryon asymmetry of the Universe through a multi-step phase transition in which SU(3) color symmetry is first broken and then restored. A spontaneous violation of B − L conservation leads to a contribution to the baryon asymmetry that becomes negligible in the final phase. The baryon asymmetry is therefore produced exclusively through the electroweak mechanism in the intermediate phase. We illustrate this scenario with a simple model that reproduces the observed baryon asymmetry. We discuss how future electric dipole moment and collider searches may probe this scenario, though future EDM searches would require an improved sensitivity of several orders of magnitude.