Abundance Of Neutralino Dark Matter Research Articles

Is the magnitude of the Peccei\u2013Quinn scale set by the landscape?

The value of the Higgs boson mass plus the lack of signal at LHC13 has led to a naturalness crisis for supersymmetric models. In contrast, rather general considerations of the string theory landscape imply a mild statistical draw towards large soft SUSY breaking terms tempered by the requirement of proper electroweak symmetry breaking where SUSY contributions to the weak scale are not too far from m_{weak}sim 100 GeV. Such a picture leads to the prediction that m_hsimeq 125 GeV while most sparticles are beyond current LHC reach. Here we explore the possibility that the magnitude of the Peccei–Quinn (PQ) scale f_a is also set by string landscape considerations within the framework of a compelling SUSY axion model. First, we examine the case where the PQ symmetry arises as an accidental approximate global symmetry from a more fundamental gravity-safe mathbb {Z}_{24}^R symmetry and where the SUSY mu parameter arises from a Kim-Nilles operator. The pull towards large soft terms then also pulls the PQ scale as large as possible. Unless this is tempered by rather severe (unknown) cosmological or anthropic bounds on the density of dark matter, then we would expect a far greater abundance of dark matter than is observed. This conclusion cannot be negated by adopting a tiny axion misalignment angle theta _i because WIMPs are also overproduced at large f_a. Hence, we conclude that setting the PQ scale via anthropics is highly unlikely. Instead, requiring soft SUSY breaking terms of order the gravity-mediation scale m_{3/2}sim 10–100 TeV places the mixed axion–neutralino dark matter abundance into the intermediate scale sweet zone where f_asim 10^{11}–10^{12} GeV. We compare our analysis to the more general case of a generic SUSY DFSZ axion model with uniform selection on theta _i but leading to the measured dark matter abundance: this approach leads to a preference for f_asim 10^{12} GeV.

Sommerfeld enhancements and relic abundance of neutralino dark matter in the general MSSM

We discuss the calculation of Sommerfeld enhancements on the neutralino LSP relic abundance calculation for heavy neutralino dark matter including co-annihilations of nearly mass-degenerate neutralino and chargino states. A newly developed EFT framework enables us to consider for the first time all (off)-diagonal potential and annihilation matrices including P- and next-to-next-to-leading order S-wave effects for a generic MSSM parameter space point, and to treat effects from heavy states perturbatively.

NLSP gluino and NLSP stop scenarios fromb−τYukawa unification

We present a study of b-tau Yukawa unified supersymmetric SU(4)_c x SU(2)_L x SU(2)_R model (with mu > 0), which predicts the existence of gluino - neutralino and stop - neutralino coannihilation scenarios compatible with the desired relic LSP neutralino dark matter abundance and other collider constraints. The NLSP gluino or NLSP stop masses vary between 400 GeV to ~ 1 TeV. The NLSP gluinos will be accessible at the 14 TeV LHC, while we hope that the NSLP stop solutions will be probed in future LHC searches. We also identify regions of the parameter space in which the gluino and the lighter stop are closely degenerate in mass, interchangeably playing the role of NLSP and NNLSP. We also update a previous study of t-b-tau Yukawa unification and show that NLSP gluino of mass ~ 1 TeV, with a mass difference between the gluino and neutralino of less than 80 GeV, can be realized consistent with the current collider and astrophysical constraints. We present benchmark points for b-tau and t-b-tau Yukawa unification that can be accessible at the LHC.

Nonthermal dark matter in string compactifications

Non-thermal cosmological histories are capable of greatly increasing the available parameter space of different particle physics dark matter (DM) models and are well-motivated by the ubiquity of late-decaying gravitationally coupled scalars in UV theories like string theory. A non-thermal DM model is presented in the context of LARGE Volume Scenarios in type IIB string theory. The model is capable of addressing both the moduli-induced gravitino problem as well as the problem of overproduction of axionic dark radiation and/or DM. We show that the right abundance of neutralino DM can be obtained in both thermal under and overproduction cases for DM masses between O(GeV) to O(TeV). In the latter case the contribution of the QCD axion to the relic density is totally negligible, while in the former case it can be comparable to that of the neutralino thus resulting in a multi-component DM scenario.

Strictly anomaly mediated supersymmetry breaking

We consider an MSSM extension with anomaly mediation as the source of supersymmetry-breaking, and a U(1) symmetry which solves the tachyonic slepton problem, and introduces both the see-saw mechanism for neutrino masses, and the Higgs mu-term. We compare its spectra with those from so-called minimal anomaly mediated supersymmetry breaking. We find a Standard Model-like Higgs of mass 125 GeV with a gravitino mass of 140 TeV and tan(beta)=16. However, the muon anomalous magnetic moment is 3 sigma away from the experimental value. The model naturally produces a period of hybrid inflation, which can exit to a false vacuum characterised by large Higgs vevs, reaching the true ground state after a period of thermal inflation. The scalar spectral index is reduced to approximately 0.975, and the correct abundance of neutralino dark matter can be produced by decays of thermally-produced gravitinos, provided the gravitino mass (and hence the Higgs mass) is high. Naturally light cosmic strings are produced, satisfying bounds from the Cosmic Microwave Background. The complementary pulsar timing and cosmic ray bounds require that strings decay primarily via loops into gravitational waves. Unless the loops are extremely small, the next generation pulsar timing array will rule out or detect the string-derived gravitational radiation background in this model.

Effects of large threshold corrections in supersymmetric type-I seesaw model

We investigate lepton flavor violating (LFV) radiative processes and the relic abundance of neutralino dark matter in supersymmetric type-I seesaw model. We carefully derive threshold corrections to the flavor off-diagonal elements of slepton mass matrix and up-type Higgs mass squared and find that they can be large in the case of large $B_N^0$. We examine how the branching ratios of LFV radiative decays and the relic abundance of neutralino dark matter can be significantly affected by the large threshold corrections. Soft scalar mass squared parameter of up-type Higgs scalar is also affected by the threshold corrections. Since the higgsino mass depends on the mass parameter for up-type Higgs, the LFV processes and the relic abundance of the neutralino dark matter are correlated with each other. We show that there are parameter regions where the predictions of the relic abundance of neutralino dark matter are consistent with WMAP observation and the branching ratios of LFV radiative decays are predicted to be testable in future experiments. We find that the masses of scalar supersymmetric particles are not necessarily small so that the branching ratios of LFV decays can be testable in future experiment, which is distinctive feature of this scenario.

Threshold corrections to the radiative breaking of electroweak symmetry and neutralino dark matter in supersymmetric seesaw model

We study the radiative electroweak symmetry breaking and the relic abundance of neutralino dark matter in the supersymmetric type I seesaw model. In this model, there exist threshold corrections to Higgs bilinear terms coming from heavy singlet sneutrino loops, which make the soft supersymmetry breaking (SSB) mass for up-type Higgs shift at the seesaw scale and thus a minimization condition for the Higgs potential is affected. We show that the required fine-tuning between the Higgsino mass parameter $\ensuremath{\mu}$ and the SSB mass for up-type Higgs may be reduced at the electroweak scale, due to the threshold corrections. We also present how the parameter $\ensuremath{\mu}$ depends on the SSB $B$-parameter for heavy singlet sneutrinos. Since the property of neutralino dark matter is quite sensitive to the size of $\ensuremath{\mu}$, we discuss how the relic abundance of neutralino dark matter is affected by the SSB $B$-parameter. Taking the SSB $B$-parameter of order of a few hundreds TeV, the required relic abundance of neutralino dark matter can be correctly achieved. In this case, dark matter is a mixture of bino and Higgsino, under the condition that gaugino masses are universal at the grand unification scale.

Yukawa unification and neutralino dark matter inSU(4)c×SU(2)L×SU(2)R

We consider a left-right symmetric SU(4){sub c}xSU(2){sub L}xSU(2){sub R} (4-2-2) model with gravity mediated supersymmetry breaking. We find that with 4-2-2 compatible nonuniversal gaugino masses, t-b-{tau} Yukawa coupling unification is consistent with neutralino dark matter abundance and with constraints from collider experiments (except (g-2){sub {mu}}). The gluino mass lies close to that of the lightest neutralino, so that the gluino coannihilation channel plays an important role in determining the neutralino relic abundance. By relaxing the Yukawa unification constraint we find stau and stop masses as low as 200-220 GeV. We highlight some benchmark points for these cases with 40{<=}tan{beta}{<=}58.

Modulus-dominated SUSY-breaking soft terms in F-theory and their test at LHC

We study the general patterns of SUSY-breaking soft terms arising under the assumption of Kahler moduli dominated SUSY-breaking in string theory models. Insisting that all MSSM gauginos get masses at leading order and that the top Yukawa coupling is of order the gauge coupling constant identifies the class of viable models. These are models in which the SM fields live either in the bulk or at the intersection of local sets of Type IIB D7-branes or their F-theory relatives. General arguments allow us to compute the dependence of the Kahler metrics of MSSM fields on the local Kahler modulus of the brane configuration in the large moduli approximation. We illustrate this study in the case of toroidal/orbifold orientifolds but discuss how the findings generalize to the F-theory case which is more naturally compatible with coupling unification. Only three types of 7-brane configurations are possible, leading each of them to very constrained patterns of soft terms for the MSSM. We study their consistency with radiative electroweak symmetry breaking and other phenomenological constraints. We find that essentially only the configuration corresponding to intersecting 7-branes is compatible with all present experimental constraints and the desired abundance of neutralino dark matter. The obtained MSSM spectrum is very characteristic and could be tested at LHC. We also study the LHC reach for the discovery of this type of SUSY particle spectra.

Neutralino dark matter from heavy axino decay

We consider cosmological consequences of a heavy axino, decaying to the neutralino in R-parity conserving models. The importance and influence of the axino decay on the resultant abundance of neutralino dark matter depends on the lifetime and the energy density of axino. For a high reheating temperature after inflation, copiously produced axinos dominate the energy density of the universe, and its decay produces a large amount of entropy. As a bonus, we obtain that the upper bound on the reheating temperature after inflation via gravitino decay can be moderated, because the entropy production by the axino decay more or less dilutes the gravitinos.

Dark matter allowed scenarios for Yukawa-unified SO(10) SUSY GUTs

Simple supersymmetric grand unified models based on the gauge group SO(10) require?in addition to gauge and matter unification?the unification of t-b-? Yukawa couplings. Owing to sparticle contributions to fermion self-energy diagrams, the Yukawa unification however only occurs for very special values of the soft SUSY breaking parameters. We perform a search using a Markov Chain Monte Carlo (MCMC) technique to investigate model parameters and sparticle mass spectra which occur in Yukawa-unified SUSY models, where we also require the relic density of neutralino dark matter to saturate the WMAP-measured abundance. For Yukawa unified models with 0$>?>0, the spectrum is characterizd by three mass scales: first and second generation scalars in the multi-TeV range, third generation scalars in the TeV range, and gauginos in the ~ 100 GeV range. Most solutions give far too high a relic abundance of neutralino dark matter. The dark matter discrepancy can be rectified by i). allowing for neutralino decay to axino plus photon, ii). imposing gaugino mass non-universality or iii). imposing generational non-universality. In addition, the MCMC approach finds a compromise solution where scalar masses are not too heavy, and where neutralino annihilation occurs via the light Higgs h resonance. By imposing weak scale Higgs soft term boundary conditions, we are also able to generate low ?,?mA solutions with neutralino annihilation via a light A resonance, though these solutions seem to be excluded by CDF/D0 measurements of the Bs ? ?+?? branching fraction. Based on the dual requirements of Yukawa coupling unification and dark matter relic density, we predict new physics signals at the LHC from pair production of 350?450 GeV gluinos. The events are characterized by very high b-jet multiplicity and a dilepton mass edge around m02?m01 ~ 50?75 GeV.

Anomalous U(1) symmetry and lepton flavor violation

We show that in a large class of models based on anomalous U(1) symmetry which addresses the fermion mass hierarchy problem, leptonic flavor changing processes are induced that are in the experimentally interesting range. The flavor violation occurs through the renormalization group evolution of the soft SUSY breaking parameters between the string scale and the U(1) A breaking scale. We derive general expressions for the evolution of these parameters in the presence of higher-dimensional operators. Several sources for the flavor violation are identified: flavor-dependent contributions to the soft masses from the U(1) A gaugino, scalar mass corrections proportional to the trace of U(1) A charge, non-proportional A-terms from vertex corrections, and the U(1) A D-term. Quantitative estimates for the decays μ→ eγ and τ→ μγ are presented in supergravity models which accommodate the relic abundance of neutralino dark matter.

Lepton flavor violation and the origin of the seesaw mechanism

The right-handed neutrino mass matrix that is central to the understanding of small neutrino masses via the seesaw mechanism can arise either (i) from renormalizable operators or (ii) from nonrenormalizable or super-renormalizable operators, depending on the symmetries and the Higgs content of the theory beyond the standard model. In this paper, we study lepton flavor violating (LFV) effects in the first class of seesaw models wherein the ${\ensuremath{\nu}}_{R}$ Majorana masses arise from renormalizable Yukawa couplings involving a $B\ensuremath{-}L=2$ Higgs field. We present detailed predictions for $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}+\ensuremath{\gamma}$ and $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e+\ensuremath{\gamma}$ branching ratios in these models taking the current neutrino oscillation data into account. Focusing on minimal supergravity models, we find that for a large range of minimal supersymmetric standard model (MSSM) parameters, suggested by the relic abundance of neutralino dark matter which is consistent with Higgs boson mass and other constraints, these radiative decays are in the range accessible to planned experiments. We compare these predictions with lepton flavor violation in the second class of models arising entirely from the Dirac Yukawa couplings. We study the dependence of the ratio $r\ensuremath{\equiv}B(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e+\ensuremath{\gamma})/B(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}\ensuremath{\mu}+\ensuremath{\gamma})$ on the MSSM parameters and show that measurement of r can provide crucial insight into the origin of the seesaw mechanism.