Stable Dark Matter Research Articles

A dark matter candidate from Lorentz invariance in 6D

We study the unique 6 dimensional orbifold with chiral fermions where a stable dark matter candidate is present due to Lorentz invariance on the orbifold, with no additional discrete symmetries imposed by hand. We propose a model of Universal Extra Dimensions where a scalar photon of few hundred GeV is a good candidate for dark matter. The spectrum of the model is characteristic of the geometry, and it has clear distinctive features compared to previous models of Kaluza-Klein dark matter. The 5 dimensional limit of this model is the minimal model of natural Kaluza-Klein dark matter. Notwithstanding the low mass range preferred by cosmology, the model will be a challenge for the LHC due to the relatively small splitting between the states in the same KK level.

Top Yukawa deviation in extra dimension

We suggest a simple one-Higgs-doublet model living in the bulk of five-dimensional spacetime compactified on S 1 / Z 2 , in which the top Yukawa coupling can be smaller than the naive standard-model expectation, i.e. the top quark mass divided by the Higgs vacuum expectation value. If we find only single Higgs particle at the LHC and also observe the top Yukawa deviation, our scenario becomes a realistic candidate beyond the standard model. The Yukawa deviation comes from the fact that the wave function profile of the free physical Higgs field can become different from that of the vacuum expectation value, due to the presence of the brane-localized Higgs potentials. In the Brane-Localized Fermion scenario, we find sizable top Yukawa deviation, which could be checked at the LHC experiment, with a dominant Higgs production channel being the WW fusion. We also study the Bulk Fermion scenario with brane-localized Higgs potential, which resembles the Universal Extra Dimension model with a stable dark matter candidate. We show that both scenarios are consistent with the current electroweak precision measurements.

ATIC/PAMELA anomaly from fermionic decaying dark matter

We demonstrate that an economical two Higgs doublet model can explain the electron and positron excesses in the recent ATIC and PAMELA experiments by the three body decays of the dark matter (DM) fermions without requiring the fine turning of the couplings and degeneracy of masses. We also show that the mass and lifetime of the decaying DM particle may not be fixed to be around 1 TeV and 10 26 s , respectively. Moreover, we note that this model includes a stable dark matter candidate as well.

Accurate Mass Determinations in Decay Chains with Missing Energy

Many beyond the standard model theories include a stable dark matter candidate that yields missing or invisible energy in collider detectors. If observed at the CERN Large Hadron Collider, we must determine if its mass and other properties (and those of its partners) predict the correct dark matter relic density. We give a new procedure for determining its mass with small error.

Gravitational lensing and structural stability of dark matter caustic rings

In a cold dark matter (CDM) paradigm, density perturbations enter the nonlinear regime of structure formation where shell crossings occur, and caustics form. A dark matter caustic is generically a surface in space where the CDM particles are naturally focussed, and hence, the density is very large. The caustic ring model of galactic halo formation predicts a minimal caustic structure classified as outer caustics and caustic rings at certain locations in the halos. It provides a well-defined density profile and geometry near the caustics. Using this model, I show that the gravitational lensing by the cusps (${A}_{\ensuremath{-}3}$ catastrophes) of caustic rings at cosmological distances may offer the tantalizing opportunity to detect CDM indirectly, and discriminate between axions and weakly interacting massive particles (WIMPs). The lensing effects of the caustic rings increase as the line of sight approaches to the cusps where it diverges in the limit of zero velocity dispersion. In the presence of finite velocity dispersion, the caustics are smeared out in space, and hence, the divergence is cut off. Primordial smearing distance of caustics may be used to obtain an upper bound for the lensing effects. Evidences found for the caustic rings, on the other hand, were used to estimate an upper bound for the smearing distance, which may be used to obtain a lower bound for the lensing effects. In that range of smearing out, the magnification of a cosmological axion caustic ring is constrained between 3% and 2800% at the outer cusp, and between 2% and 46% at the nonplanar cusps. For a cosmological WIMP caustic ring, the magnification is constrained between 3% and 28% at the outer cusp, and between 2% and 5% at the nonplanar cusps. As pointlike background sources cross behind the axion (WIMP) folds, the time scale of brightness change is about an hour (a year). Thus, they may be used to probe the cusps and discriminate between axions and WIMPs by present instruments. Finally, I derive and analyze the catastrophe function of the triaxial caustic rings to prove rigorously that they are structurally stable.

Gravitino, axino, and Kaluza–Klein graviton warm and mixed dark matter andreionization

Stable particle dark matter may well originate during the decay of long-lived relic particles,as recently extensively examined in the cases of the axino, gravitino, and higherdimensional Kaluza–Klein (KK) graviton. It is shown that in much of the viableparameter space such dark matter emerges naturally warm/hot or mixed. Inparticular, decay produced gravitinos (KK gravitons) may only be considered cold forthe mass of the decaying particle in the several TeV range, unless the decayingparticle and the dark matter particle are almost degenerate. Such dark mattercandidates are thus subject to a host of cosmological constraints on warm andmixed dark matter, such as limits from a proper reionization of the Universe, theLyman-α forest, and the abundance of clusters of galaxies. It is shown that constraints from an earlyreionization epoch, such as are indicated by recent observations, may potentially limit suchwarm/hot components to contributing only a very small fraction to the dark matter.

Predicting the seesaw scale in a minimal bottom-up extension of the MSSM

We analyze a minimal bottom-up seesaw scenario where we require the theory to satisfy three phenomenological conditions: (i)it is supersymmetric; (ii) it has a local B-L symmetry as part of the SU(2)_L x SU(2)_R x U(1)_{B-L} gauge theory to implement the seesaw mechanism and (iii) B-L symmetry breaking is such that it leaves R-parity unbroken giving a naturally stable dark matter. We show that in such a theory, one can predict the seesaw scale for neutrino masses to be M_R ~ \sqrt{M_{SUSY} M_{Pl}} ~ 10^{11} GeV. We show that the ground state with this property is a stable minimum and is lower than possible electric charge violating minimum in this theory. Such models in their generic version are known to predict the existence of a light doubly charged Higgs boson and Higgsino which can be searched for in collider experiments. We give expressions for their masses in this minimal version. We then indicate how one can get different expectation values for the MSSM Higgs doublets in the theory required to have realistic quark masses.

Neutrino mixing predictions of a minimal SO(10) model with suppressed proton decay

During the past year, a minimal renormalizable supersymmetric SO(10) model has been proposed with the following properties: it predicts a naturally stable dark matter and neutrino mixing angles theta_atm and theta_13 while at the same time accommodating CKM CP violation among quarks with no SUSY CP problem. Suppression of proton decay for all allowed values of tan beta strongly restricts the flavor structure of the model making it predictive for other processes as well. We discuss the following predictions of the model in this paper, e.g. down-type quark masses, and neutrino oscillation parameters, U_e3, delta_MNSP, which will be tested by long baseline experiments such as T2K and subsequent experiments using the neutrino beam from JPARC. We also calculate lepton flavor violation and the lepton asymmetry of the Universe in this model.

Proton decay in a minimal SUSY SO(10) model for neutrino mixings

A minimal renormalizable SUSY SO(10) model with B–L symmetry broken by 126 Higgs field has recently been shown to predict all neutrino mixings and the ratio Δm2⊙/Δm2A in agreement with observations. Unlike models where B–L is broken by 16 Higgs, this model guarantees automatic R-parity conservation and hence a stable dark matter as well as the absence of dim=4 baryon violating operator without any additional symmetry assumptions. In this paper, we discuss the predictions of the model for proton decay induced at the GUT scale. We scan over the parameter space of the model allowed by neutrino data and find upper bounds on the partial lifetime for the modes τ(n→π0ν̄)=2τ(p→π+ν̄)⩽(5.7−13)×1032 yrs and τ(n→K0ν̄)⩽2.97×1033 yrs for the average squark mass of a TeV and wino mass of 200 GeV, when the parameters satisfy the present lower limits on τ(p→K+ν̄) mode. These results can be used to test the model.

Scalar dark matter candidates

We investigate the possibility that dark matter could be made of scalar candidates and focus, in particular, on the unusual mass range between a few MeVs and a few GeVs. After showing why the Lee–Weinberg limit (which usually forbids a dark matter mass below a few GeVs) does not necessarily apply in the case of scalar particles, we discuss how light candidates ( m dm< O(GeV)) can satisfy both the gamma ray and relic density constraints. We find two possibilities. Either dark matter is coupled to heavy fermions (but if m dm≲100 MeV, an asymmetry between the dark matter particle and antiparticle number densities is likely to be required), or dark matter is coupled to a new light gauge boson U. The (collisional) damping of light candidates is, in some circumstances, large enough to be mentioned, but in most cases too small to generate a non-linear matter power spectrum at the present epoch that differs significantly from the cold dark matter spectrum. On the other hand, heavier scalar dark matter particles (i.e., with m dm≳ O(GeV)) turn out to be much less constrained. We finally discuss a theoretical framework for scalar candidates, inspired from theories with N=2 extended supersymmetry and/or extra space dimensions, in which the dark matter stability results from a new discrete (or continuous) symmetry.