LHC Benchmark Scenarios for the Real Higgs Singlet Extension of the Standard Model

We present benchmark scenarios for searches for an additional Higgs state in the real Higgs singlet extension of the Standard Model in Run 2 of the LHC. The scenarios are selected such that they fulfill all relevant current theoretical and experimental constraints, but can potentially be discovered at the current LHC run. We take into account the results presented in earlier work and update the experimental constraints from relevant LHC Higgs searches and signal rate measurements. The benchmark scenarios are given separately for the low mass and high mass region, i.e. the mass range where the additional Higgs state is lighter or heavier than the discovered Higgs state at around 125 GeV. They have also been presented in the framework of the LHC Higgs Cross Section Working Group.Comment: 23 pages, 9 tables, 4 figures. arXiv admin note: text overlap with arXiv:1501.02234; v2: one subsection, one figure, and some references added, minor errors corrected. Corresponds to published journal versio

Constraining Extended Scalar Sectors at the LHC and beyond

We give a brief overview of beyond the Standard Model (BSM) theories with an extended scalar sector and their phenomenological status in the light of recent experimental results. We discuss the relevant theoretical and experimental constraints, and show their impact on the allowed parameter space of two specific models: the real scalar singlet extension of the Standard Model (SM) and the Inert Doublet Model. We emphasize the importance of the LHC measurements, both the direct searches for additional scalar bosons, as well as the precise measurements of properties of the Higgs boson of mass 125 GeV. We show the complementarity of these measurements to electroweak and dark matter observables.Comment: 18 pages, 8 figures; prepared for submission to MPLA (invited review) v2: several references and small text modification added to align with journal version. 2 small errors in plots correcte

The Electroweak Phase Transition in the Inert Doublet Model

We study the strength of a first-order electroweak phase transition in the Inert Doublet Model (IDM), where particle dark matter (DM) is comprised of the lightest neutral inert Higgs boson. We improve over previous studies in the description and treatment of the finite-temperature effective potential and of the electroweak phase transition. We focus on a set of benchmark models inspired by the key mechanisms in the IDM leading to a viable dark matter particle candidate, and illustrate how to enhance the strength of the electroweak phase transition by adjusting the masses of the yet undiscovered IDM Higgs states. We argue that across a variety of DM masses, obtaining a strong enough first-order phase transition is a generic possibility in the IDM. We find that due to direct dark matter searches and collider constraints, a sufficiently strong transition and a thermal relic density matching the universal DM abundance is possible only in the Higgs funnel regime.Comment: 22 pages, 1 figure. Improved comments on gauge invariance. Matches published versio

The Not-So-Well Tempered Neutralino

Light electroweakinos, the neutral and charged fermionic supersymmetric partners of the Standard Model $\mathrm{SU}(2)\times\mathrm{U}(1)$ gauge bosons and of the two $\mathrm{SU}(2)$ Higgs doublets, are an important target for searches for new physics with the Large Hadron Collider (LHC). However, if the lightest neutralino is the dark matter, constraints from direct dark matter detection experiments rule out large swaths of the parameter space accessible to the LHC, including in large part the so-called "well-tempered" neutralinos. We focus on the Minimal Supersymmetric Standard Model (MSSM) and explore in detail which regions of parameter space are not excluded by null results from direct dark matter detection, assuming exclusive thermal production of neutralinos in the early universe, and illustrate the complementarity with current and future LHC searches for electroweak gauginos. We consider both bino-Higgsino and bino-wino "not-so-well-tempered" neutralinos, i.e. we include models where the lightest neutralino constitutes only part of the cosmological dark matter, with the consequent suppression of the constraints from direct and indirect dark matter searches.Comment: 14 pages, 6 figures; v2: minor modifications, matches published versio

The Impact of Two-Loop Effects on the Scenario of MSSM Higgs Alignment without Decoupling

In multi-Higgs models, the properties of one neutral scalar state approximate those of the Standard Model (SM) Higgs boson in a limit where the corresponding scalar field is roughly aligned in field space with the scalar doublet vacuum expectation value. In a scenario of alignment without decoupling, a SM-like Higgs boson can be accompanied by additional scalar states whose masses are of a similar order of magnitude. In the Minimal Supersymmetric Standard Model (MSSM), alignment without decoupling can be achieved due to an accidental cancellation of tree-level and radiative loop-level effects. In this paper we assess the impact of the leading two-loop O(alpha_s h_t^2) corrections on the Higgs alignment condition in the MSSM. These corrections are sizable and important in the relevant regions of parameter space and furthermore give rise to solutions of the alignment condition that are not present in the approximate one-loop description. We provide a comprehensive numerical comparison of the alignment condition obtained in the approximate one-loop and two-loop approximations, and discuss its implications for phenomenologically viable regions of the MSSM parameter space.Comment: 31 pages, 7 figure

Higgs Couplings and Supersymmetry in the Light of early LHC Results

We present phenomenological studies investigating the implications of early results from the Large Hadron Collider (LHC) for models beyond the Standard Model (BSM), mostly focusing on Supersymmetry (SUSY). Our work covers different aspects in this wide field of research. We describe the development and basic concepts of the public computer codes HiggsBounds (version 4) and HiggsSignals. These confront the Higgs sector predictions of BSM models with results from LEP, Tevatron and LHC Higgs searches. While HiggsBounds tests the model against experimental null-results, HiggsSignals evaluates the model’s chi-squared compatibility with the signal rate and mass measurements of the Higgs boson, that was discovered by the LHC in 2012. We then perform a systematic study of potential deviations in the Higgs couplings from their Standard Model (SM) prediction. No significant deviations are found. Future capabilities of Higgs coupling determination at the later LHC stages and at the International Linear Collider (ILC) are explored. We also study the implications of the Higgs discovery for the Minimal Supersymmetric Standard Model (MSSM), considering either the light or the heavy CP-even Higgs boson as the discovered state. We show that both interpretations are viable and discuss their phenomenology. Finally, we study the LHC signatures of resonant scalar lepton production, which may arise in SUSY models with R-parity violation (RPV). These are confronted with early LHC results, yielding constraints on the relevant RPV operators

Dark Matter Inelastic Up-Scattering with the Interstellar Plasma: An Exciting New Source of X-Ray Lines, including at 3.5 keV

We explore the phenomenology of a class of models where the dark matter particle can inelastically up-scatter to a heavier excited state via off-diagonal dipolar interactions with the interstellar plasma (gas or free electrons). The heavier particle then rapidly decays back to the dark matter particle plus a quasi-monochromatic photon. For the process to occur at appreciable rates, the mass splitting between the heavier state and the dark matter must be comparable to, or smaller than, the kinetic energy of particles in the plasma. As a result, the predicted photon line falls in the soft X-ray range, or, potentially, at arbitrarily lower energies. We explore experimental constraints from cosmology and particle physics, and present accurate calculations of the dark matter thermal relic density and of the flux of monochromatic X-rays from thermal plasma excitation. We find that the model provides a natural explanation for the observed 3.5 keV line from clusters of galaxies and from the Galactic center, and is consistent with null detections of the line from dwarf galaxies. The unique line shape, which will be resolved by future observations with the Hitomi (formerly Astro-H) satellite, and the predicted unique morphology and target-temperature dependence will enable easy discrimination of this class of models versus other scenarios for the generation of the 3.5 keV line or of any other unidentified line across the electromagnetic spectrum.Comment: 16 pages, 9 figures; v2, version published in Physical Review