Classification of dark pion multiplets as dark matter candidates and collider phenomenology

In this work we propose to use leading singularities to obtain the classical pieces of amplitudes of two massive particles whose only interaction is gravitational. Leading singularities are generalizations of unitarity cuts. At one-loop we find that leading singularities obtained by multiple discontinuities in the t-channel contain all the classical information. As the main example, we show how to obtain a compact formula for the fully relativistic classical one-loop contribution to the scattering of two particles with different masses. The non-relativistic limit of the leading singularity agrees with known results in the post-Newtonian expansion. We also compute a variety of higher loop leading singularities including some all-loop families and study some of their properties.     

Inelastic dark matter at the LHC

The dark matter sector may be more complicated than anticipated. An inelastically scattering dark matter with a mass splitting above one MeV will make direct detection experiments hopeless, and render LHC the primary chance for discovery. We perform a model-independent study of inelastic dark matter at the LHC, concentrating on the parameter space with the mass splitting between the excited and ground states of dark matter above a few hundred MeV. The generic signatures of inelastic dark matter at the LHC are displaced pions together with a monojet plus missing energy, and can be tested at the 7 TeV LHC.     

Dark matter and LHC phenomenology of a scale-invariant scotogenic model

We study the phenomenology of a model that addresses the neutrino mass, dark matter, and generation of the electroweak scale in a single framework. Electroweak symmetry breaking is realized via the Coleman-Weinberg mechanism in a classically scale invariant theory, while the neutrino mass is generated radiatively through interactions with dark matter in a typically scotogenic manner. The model introduces a scalar triplet and singlet and a vectorlike fermion doublet that carry an odd parity of Z_2, and an even parity scalar singlet that helps preserve classical scale invariance. We sample over the parameter space by taking into account various experimental constraints from the dark matter relic density and direct detection, direct scalar searches, neutrino mass, and charged lepton flavor violating decays. We then examine by detailed simulations possible signatures at the LHC to find some benchmark points of the free parameters. We find that the future high-luminosity LHC will have a significant potential in detecting new physics signals in the dilepton channel.     

Supersymmetric candidates for nonbaryonic dark matter

We analyze how detectability of relic neutralinos by direct means is related to their local and cosmological densities. We show to what extent the present experiments of direct searches for weakly interacting massive particles, when interpreted in terms of relic neutralinos, probe interesting regions of the supersymmetric parameter space. Our analysis is performed in a number of different supersymmetric schemes.     

Q-ball candidates for self-interacting dark matter

We show that nontopological solitons, known as Q-balls, are promising candidates for self-interacting dark matter. They can satisfy the cross-section requirements for a broad range of masses. Unlike previously considered examples, Q-balls can stick together after collision, reducing the effective self-interaction rate to a negligible value after a few collisions per particle. This feature modifies predictions for halo formation. We also discuss the possibility that Q-balls have large interaction cross sections with ordinary matter.     

Higgs portal,fermionic dark matter,and a Standard Model like Higgs at 125 GeV

We show that fermionic dark matter (DM) which communicates with the Standard Model (SM) via the Higgs portal is a viable scenario, even if a SM-like Higgs is found at around 125 GeV. Using effective field theory we show that for DM with a mass in the range from about 60 GeV to 2 TeV the Higgs portal needs to be parity violating in order to be in agreement with direct detection searches. For parity conserving interactions we identify two distinct options that remain viable: a resonant Higgs portal, and an indirect Higgs portal. We illustrate both possibilities using a simple renormalizable toy model.     

Naturalness,supersymmetry and implications for LHC and dark matter

It is shown that the Hyperbolic Branch of the radiative electroweak symmetry breaking contains in it three regions: the Focal Point, Focal Curves, and Focal Surfaces. Further, the Focal Point is shown to lie on the boundary of a Focal Curve. These focal regions allow for a small μ while scalar masses can become large and may lie in the several TeV region. It is shown that for the mSUGRA model the current LHC-7 constraint depletes the Focal Point region while regions on Focal Curves and Focal Surfaces remain largely intact. The LHC implications for models which lie on Focal Curves are briefly discussed as well as the implications of dark matter constraints for the Focal Point, Focal Curves and Focal Surfaces are discussed.     

Heavy scalar boson in view of the unconfirmed 750 GeV LHC diphoton excess

We discuss the impact of the constraints from the measurements of the parameters of the observed 125 GeV Higgs boson and from the unconfirmed 750 GeV diphoton excess in the LHC experiments on the properties of a possible extra scalar boson predicted in various Standard Model extensions. We consider an SM extension based on a stabilized brane-world model, in which the effective low-energy Lagrangian for the scalar degrees of freedom turns out to be very general and, for different values of the model parameters, reproduces the scalar field Lagrangians of various SM extensions by a singlet scalar. It is shown that in the simplest variant of the model, where only the gravitational degrees of freedom propagate in the bulk, the 125 GeV scalar state can be consistently interpreted as a Higgs-dominated state for a rather wide range of the model parameters, whereas the production cross section of a heavier radion-dominated state with mass 750 GeV or more turns out to be too small in the allowed region of the model parameter space for producing the wouldbe diphoton excess.     

Photonic dark matter portal and quantum physics

We study a model of dark matter in which the hidden sector interacts with standard model particles via a hidden photonic portal.We investigate the effects of this new interaction on the hydrogen atom,including the Stark,Zeeman and hyperfine effects.Using the accuracy of the measurement of energy,we obtain an upper bound for the coupling constant of the model as f≤10~(-12).We also calculate the contribution from the hidden photonic portal to the anomalous magnetic moment of the muon as α_μ≤ 2.2 × 10~(-23)(for the dark particle mass scale 100MeV),which provides an important probe of physics beyond the standard model.     

Light dark matter in NMSSM and implication on Higgs phenomenology

For the experimental search of neutralino dark matter, it is important to know its allowed mass and scattering cross section with the nucleon. In order to figure out how light a neutralino dark matter can be predicted in low energy supersymmetry, we scan over the parameter space of the NMSSM (next-to-minimal supersymmetric model), assuming all the relevant soft mass parameters to be below TeV scale. We find that in the parameter space allowed by current experiments the neutralino dark matter can be as light as a few GeV and its scattering rate off the nucleon can reach the sensitivity of XENON100 and CoGeNT. As a result, a sizable parameter space is excluded by the current XENON100 and CoGeNT data (the plausible CoGeNT dark matter signal can also be explained). The future 6000 kg-days exposure of XENON100 will further explore (but cannot completely cover) the remained parameter space. Moreover, we find that in such a light dark matter scenario a light CP-even or CP-odd Higgs boson must be present to satisfy the measured dark matter relic density. Consequently, the SM-like Higgs boson hSM may decay predominantly into a pair of light Higgs bosons or a pair of neutralinos so that the conventional decays like hSM→γγ is much suppressed.     

String consistency,heavy exotics,and the 750 GeV diphoton excess at the LHC

String consistency conditions are stronger than anomaly cancellation and can require the addition of exotics in the visible sector. We study such exotics and demonstrate that they may account for the modest excess at 750 GeV in recent diphoton resonance searches performed by the ATLAS and CMS collaborations. In a previous analysis of type II MSSM D‐brane quivers we systematically added up to five exotics for the sake of satisfying string consistency conditions. Using this dataset, we demonstrate that 89780 of the 89964 quivers have exotics, 78155 of which include singlets that may couple to MSSM or exotic multiplets with coupling structures governed by U(1) symmetries that are often anomalous. We demonstrate that certain sets of exotics are far preferred over others and study the structure of singlet couplings to heavy exotics carrying standard model charges. Typical possibilities include singlets that may decay to vector‐like quarks and/or vector‐like leptons and subsequently to two photons. We show that a narrow width diphoton excess can be accounted for while evading existing bounds if multiple exotics are added, with vector‐like leptons of mass GeV and vector‐like quarks with masses up to ≃ 3 TeV. However, a large width , as suggested by the ATLAS data, cannot be easily accommodated in this framework. Renormalization group equations with GUT‐scale boundary conditions show that these supersymmetric models are perturbative and stable. Type IIA compactifications on toroidal orbifolds allow for O(10) Yukawa couplings in the ultraviolet. We also discuss the possibility of accounting for the diphoton excess in a low string scale scenario via the decay of string axions.     

2HDM portal for singlet-doublet dark matter

We present an extensive analysis of a model in which the (Majorana) Dark Matter candidate is a mixture between a SU(2) singlet and two SU(2) doublets. This kind of setup takes the name of singlet-doublet model. We will investigate in detail an extension of this model in which the Dark Matter sector interactions with a 2-doublet Higgs sector enforcing the complementarity between Dark Matter phenomenology and searches of extra Higgs bosons.