Table of contents

The seventh international workshop 'The Dark Side of the Universe (DSU 2011)' was organized by The Kavli Institute for Theoretical Physics China (KITPC), from 26–30 September 2011 in Beijing. DSU 2011 is a continuation of DSU workshops previously held in Seoul (2005), Madrid (2006), Minnesota (2007), Cairo (2008), Melbourne (2009) and Leon (2010). The workshop was associated with the KTIPC program 'Dark matter and new physics', 21 September–6 November, 2011. The topics of the workshop include: dark matter candidates and theory, direct, indirect and accelerator dark matter searches, baryogenesis, new physics beyond the standard model, the origin of dark energy, experimental aspects of dark energy, nonstandard cosmology and astroparticle physics and Ultra hight energy cosmic rays etc.

The workshop attracted more than 130 participants from more than ten countries and regions. The talks presented at the workshop can be downloaded from the websitehttp://kitpc.itp.ac.cn/dsu2011.

The workshop is financially supported by the Chinese Academy of Sciences, the National Science Foundation China (NSFC), and the China Center of Advance Science and Technology (CCAST).

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

No known astrophysical process can generate a monoenergetic gamma-ray with energy in the TeV range, resulting in very stringent constraints on the lifetime of dark matter particles which decay producing gamma-ray lines. We derive in this work constraints on the decay width from observations at current IACTs as well as the estimated sensitivity of the projected CTA. We also discuss the implications of these limits for two dark matter models where the dark matter particle decays at tree level producing gamma-ray lines, namely the gravitino in supersymmetric models without R-parity conservation and a vector of a hidden SU(2) gauge group. We also discuss the constraints on scenarios where the gamma-ray line is generated at the one loop level.

Successfully launched in June 2008, the Fermi Gamma-ray Space Telescope, formerly named GLAST, has been observing the high-energy gamma-ray sky with unprecedented sensitivity in the 20MeV 300GeV energy range and electrons + positrons in the 7 GeV − 1 TeV range, opening a new observational window on a wide variety of astrophysical objects.

We review the formalism for spin-dependent WIMP-nucleus elastic scattering discussing the simplification obtained using the normalized spin structure functions and some applications.

The μνSSM is a supersymmetric model that has been proposed to solve the problems generated by other supersymmetric extensions of the standard model of particle physics. Given that R-parity is broken in the μνSSM, the gravitino is a natural candidate for decaying dark matter since its lifetime becomes much longer than the age of the Universe. In this model, gravitino dark matter could be detectable through the emission of a monochromatic gamma ray in a two-body decay. We study the prospects of the Fermi-LAT telescope to detect such monochromatic lines in 5 years of observations of the most massive nearby extragalactic objects. The dark matter halo around the Virgo galaxy cluster is selected as a reference case, since it is associated to a particularly high signal-to-noise ratio and is located in a region scarcely affected by the astrophysical diffuse emission from the galactic plane. The simulation of both signal and background gamma-ray events is carried out with the Fermi Science Tools, and the dark matter distribution around Virgo is taken from a N-body simulation of the nearby extragalactic Universe, with constrained initial conditions provided by the CLUES project. We find that a gravitino with a mass range of 0.6-2 GeV, and with a lifetime range of about 3 × 10²⁷ − 2 × 10²⁸ s would be detectable by the Fermi-LAT with a signal-to-noise ratio larger than 3. We also obtain that gravitino masses larger than about 4 GeV are already excluded in the μνSSM by Fermi-LAT data of the galactic halo.

The DAMA/LIBRA experiment is running at LNGS; it has a sensitive mass of about 250 kg highly radiopure NaI(Tl) and it is mainly devoted to the investigation of Dark Matter (DM) particles in the Galactic halo by exploiting the model independent DM annual modulation signature. The present DAMA/LIBRA experiment and the former DAMA/NaI one (the first generation experiment having an exposed mass of about 100 kg) have released so far results corresponding to a total exposure of 1.17 ton × yr, collected over 13 annual cycles. They provide a model independent evidence of the presence of DM particles in the galactic halo at 8.9 σ C.L. Some obtained results are shortly summarized and future perspectives mentioned.

In this talk I have presented the data analysis results of extracting properties of halo WIMPs: the mass and the (ratios between the) spin-independent and spin-dependent couplings/cross sections on nucleons by the AMIDAS website by taking into account possible unrejected background events in the analyzed data sets. Although non-standard astronomical setup has been used to generate pseudodata sets for our analyses, it has been found that, without prior information/assumption about the local density and velocity distribution of halo Dark Matter, these WIMP properties have been reconstructed with ∼ 2% to ≲ 30% deviations from the input values.

The channeling of the recoiling nucleus in crystalline detectors after a WIMP collision would produce a larger scintillation or ionization signal in direct detection experiments than otherwise expected. I present estimates of channeling fractions obtained using analytic models developed from the 1960's onwards to describe channeling and blocking effects. We find the fractions to be too small to affect the fits to potential WIMP candidates. I also examine the possibility of detecting a daily modulation of the dark matter signal due to channeling.

Dark Matter research at Jefferson Lab started in 2006 with the LIght Pseudoscalar and Scalar Search (LIPSS) collaboration to check the validity of results reported by the PVLAS collaboration. In the intervening years interest in dark matter laboratory experiments has grown at Jefferson Lab. Current research underway or in planning stages probe various mass regions covering 14 orders of magnitude: from 10⁻⁶ eV to 100 MeV. This presentation will be an overview of our dark matter searches, three of which focus on the hypothesized A' gauge boson.

The observed density of dark matter is of the magnitude expected for a thermal relic weakly-interacting massive particle (WIMP). In addition, the observed baryon density is within an order of magnitude of the dark matter density. This suggests that the baryon density is physically related to a typical thermal relic WIMP dark matter density. We present a model which simultaneously generates thermal relic WIMP-like densities for both baryons and dark matter by modifying a large initial baryon asymmetry. Production of unstable scalars carrying baryon number at the LHC would be a clear signature of the model.

The effect of 2010 and 2011 LHC data are discussed in connection to the potential for the direct detection of supersymmetric dark matter. The impact of the recent XENON100 results are contrasted to these predictions. Expectations for indirect detection are also discussed.

Future direct detection gravitational wave experiments would provide vital information on the early Universe. It may enable us to determine the reheating temperature by detecting a signature of reheating on the spectrum of the inflationary gravitational wave background. We investigate the detectability of the reheating signature and discuss its implications for particle physics, especially on the scenario where gravitinos are dark matter candidates.

We present an updated analysis of the constrained minimal supersymmetric standard model with μ > 0 supplemented by an 'asymptotic' Yukawa coupling quasi-unification condition, which allows an acceptable b-quark mass. Imposing constraints from the cold dark matter abundance in the universe, B physics, the muon anomalous magnetic moment, and the mass m_h of the lightest neutral CP-even Higgs boson, we find that the lightest neutralino cannot act as a cold dark matter candidate. This is mainly because the upper bound on the lightest neutralino relic abundance from cold dark matter considerations, despite the fact that this abundance is drastically reduced by neutralino-stau coannihilations, is incompatible with the recent data on the branching ratio of B_s → μ⁺μ⁻. Allowing for a different particle, such as the axino or the gravitino, to be the lightest supersymmetric particle and, thus, constitute the cold dark matter in the universe, we find that the predicted m_h's in our model favor the range (119 – 126) GeV.

Direct Dark Matter detection with cryodetectors is briefly discussed, with particular mention of the possibility of the identification of the recoil nucleus. Preliminary results from the CRESST II Dark Matter search, with 730 kg-days of data, are presented. Major backgrounds and methods of identifying and dealing with them are indicated.

The next-to-minimal supersymmetric standard model (NMSSM) is a R-parity conserving model that solves the μ-problem of the minimal supersymmetric standard model (MSSM) by adding a singlet superfield. Here we study different aspects of this model. Firstly, using Bayesian statistics, we discuss the constrained next-to-minimal supersymmetric standard model (CNMSSM) scenario. We place special emphasis on analysing the neutralino as a dark matter candidate. Additionally, using the nested sampling (NS) algorithm, we focus our analysis on a particular region of the parameter space. Results obtained scanning the low energy parameter space of the NMSSM, searching for low mass neutralinos, are discussed.

A primordial ⁷Li abundance inferred from observations of metal-poor halo stars is a factor of about three smaller than predictions of standard big bang nucleosynthesis (BBN) model. Some particle models beyond the standard model include heavy long-lived colored particles with mass much larger than 1 GeV. They would be confined inside exotic heavy hadrons, i.e., strongly interacting massive particles. We have found possible reactions which destroy ⁷Be and ⁷Li in the scenario of BBN including a long-lived sub-strongly interacting massive particle (sub-SIMP, X). The destruction is associated with non radiative X captures of the nuclei, and it can be realized only if the interaction strength between an X and a nucleon is properly weaker than that between two nucleons. Binding energies of nuclei to an X and nuclear reaction rates associated with the X are estimated. We perform a network BBN calculation using the estimated rates, and suggest that the ⁷Li problem can be solved if long-lived sub-SIMPs have existed.

Via a Bayesian likelihood analysis using 219 cosmic ray data points we extract the anomalous part of the cosmic e^± flux. First we show that a serious tension exists between the e fluxes and the rest of the data. Interpreting this tension as effect of an anomalous component on the e^± related data, we then infer the values of selected cosmic ray propagation parameters excluding the anomalous data sample from the analysis. Based on these values we calculate background predictions with theoretical uncertainties for PAMELA and Fermi-LAT. We find a statistically significant deviation between the Fermi-LAT e⁻ + e⁺ data and the predicted background even when (systematic) uncertainties are taken into account. Identifying this deviation as an anomalous e^± contribution, we make an attempt to distinguish between various sources that may be responsible for the anomalous e^± flux.

We investigate the prospects for detection of lepton flavour violation (LFV) in sparticle production and decays at a Linear Collider (LC). We study the Constrained Minimal Supersymmetric extension of the Standard Model (CMSSM), focusing on the subset of the supersymmetric parameter space that also leads to cosmologically interesting values of the relic neutralino LSP density. Emphasis is given to the complementarity between the LC and the LHC signals.

We consider models with extra U(1)' gauge symmetry that is broken spontaneously. In the models, there are cold dark matter candidates which are charged under U(1)' symmetry. Depending on the charge assignment, we can evade the strong bound from the Drell-Yang process, and consider the scenario that the dark matters strongly interact with the fermions in the Standard Model through the extra gauge boson exchanging. As an illustrative example, we discuss a supersymmetric gauged U(1)_B × U(1)_L model and see that not only correct relic density but also the DAMA/CoGeNT excess can be achieved by the dark matters.

In this talk, based on the paper 1109.3516, we consider theories where the dark matter particle carries lepton flavor quantum numbers, and has renormalizable contact interactions with the Standard Model fields. We find that the region of parameter space where dark matter has the right abundance to be a thermal relic is in general within reach of current direct detection experiments. In order to evaluate the collider prospects, we focus on a class of models where dark matter carries tau flavor, and show that the collider signals of these models include events with four or more isolated leptons and missing energy. A significant part of parameter space in these theories can be discovered above Standard Model backgrounds at the 14 TeV Large Hadron Collider. We also study the extent to which flavor and charge correlations among the final state leptons allows models of this type to be distinguished from theories where dark matter couples to leptons but does not carry flavor, similarly to a neutralino.

In this paper, the recent results from KIMS (Korea invisible mass search) experiment are presented. KIMS has searched for WIMPs (Weakly Interactig Massive Particles) scattering off the nucleus by using the CsI(Tℓ) scintillator. The detector is an array of 12 CsI(Tℓ) scintilltors, whose total mass is 103.4 kg. The results reported here used the exposure of 24524.3 kg-days. With pulse shape discrimination (PSD) analysis, we estimated the nuclear recoil (NR) event rate and no meaningful excess of NR events rate were found. From this, we derived the improved cross section limit for WIMP–nucleon interaction.

The low mass (10 GeV scale) dark matter is indicted and favored by several recent dark matter direct detection experimental results, such as DAMA and CoGeNT. In this talk, we discuss some aspects of the low mass dark matter. We study the indirect detection of dark matter through neutrino flux from their annihilation in the center of the Sun, in a class of models where the dark matter-nucleon spin-independent interactions break the isospin symmetry. The indirect detection using neutrino telescopes can impose a relatively stronger constraint and brings tension to such explanation, if the dark matter self-annihilation is dominated by heavy quarks or τ-lepton final states. The asymmetric dark matter doesn't suffer the constraints from the indirect detection results. We propose a model of asymmetric dark matter where the matter and dark matter share the common origin, the asymmetries in both the matter and dark matter sectors are simultaneously generated through leptogenesis, and we explore how this model can be tested in direct search experiments.

Neutrino mass and dark matter may be closely connected. I briefly review the status of neutrino oscillations along with neutrino mass generation schemes which suggest dark matter candidates, briefly discussing their properties and relevant direct/indirect/collider detection prospects.

The differential event rate for direct detection of dark matter, both the time averaged and the modulated one due to the motion of the Earth, are discussed. The calculations focus on relatively light cold dark matter candidates (WIMP) and low energy transfers. It is shown that for some WIMP masses the modulation amplitude may change sign. This effect can be exploited to yield information about the mass of the dark matter candidate.

In interacting multi-component dark matter (DM) models, the interactions between the DM components can covert relatively heavy DM components into lighter ones at late times after the thermal decoupling. As a consequence, the relic density of the lightest DM component can be greatly enhanced at late times, which can lead to an alternative source of boost factor required to explain the positron and electron excesses reported by the recent DM indirect search experiments.

We employ third family Yukawa unification, predicted by simple supersymmetric SO(10) models, to estimate the lightest MSSM Higgs boson mass. For μ > 0 (or μ < 0) and m_t = 173.1 GeV, the Higgs mass is estimated to lie close to 123-124 GeV. The theoretical uncertainty in this estimate is ±3 GeV. We highlight some LHC testable benchmark points which also display the presence of neutralino-stau coannihilation channel.

The RνMDM model relates radiative seesaw and minimal dark matter mass scales without imposing any beyond the Standard Model (SM) gauge symmetry. The model contains, besides the SM particles, a Majorana fermion multiplet N_R and a scalar multiplet χ which transform under the SM gauge group as (1, 5, 0) and (1, 6, −1/2). We study the dark matter physics of this model and the relevant lepton flavor violating processes.

We present a model of the gravitational field based on two symmetric tensors. The equations of motion of test particles are derived: Massive particles do not follow a geodesic but massless particles trajectories are null geodesics of an effective metric. Outside matter, the predictions of the model coincide exactly with General Relativity, so all classical tests are satisfied. In Cosmology, we get accelerated expansion without a cosmological constant.

We regard the Casimir energy of the universe as the main contribution to the cosmological constant. Using 5 dimensional models of the universe, the flat model and the warped one, we calculate Casimir energy. Introducing the new regularization, called sphere lattice regularization, we solve the divergence problem. The regularization utilizes the closed-string configuration. We consider 4 different approaches: 1) restriction of the integral region (Randall-Schwartz), 2) method of 1) using the minimal area surfaces, 3) introducing the weight function, 4) generalized path-integral. We claim the 5 dimensional field theories are quantized properly and all divergences are renormalized. At present, it is explicitly demonstrated in the numerical way, not in the analytical way. The renormalization-group function (β-function) is explicitly obtained. The renormalization-group flow of the cosmological constant is concretely obtained.

We consider Friedmann-Lemaître-Robertson-Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity in two different cases: in the dust matter dominated era and in the potential dominated era. Motivated by the local weak field constraints and by cosmological observations, we develop and use an approximation scheme for the regime close to the so-called limit of general relativity. The ensuing nonlinear approximate equations for the scalar field and the Hubble parameter can be solved analytically in cosmological time in both cases. We find criteria for the functions ω and V characterizing a scalar-tensor theory, to determine whether the theory does or does not possess solutions converging to general relativity asymptotically in time. The converging solutions can be subsumed under two principal classes: exponential or polynomial convergence, and damped oscillations around general relativity. The classes of scalar-tensor theories of gravity which contain these types of solutions and satisfy observational constraints, are candidates to explain possible deviations from the standard ΛCDM model. Finally, the effective equation of state parameter w_eff is used to illustrate possible asymptotic cosmological dynamics.

We review our recent work [1] on gravitational waves in viable f(R) models. We concentrate on the exponential gravity and Starobinsky models. We show that in both cases, the mass of the scalar mode is order of 10⁻³³eV when it propagates in vacuum. In the presence of matter density, such as galaxy, the scalar mode can be heavy. In particular, it becomes almost infinity so that the scalar mode of gravitational wave for the exponential model disappears like the ACDM, whereas it can be as low as 10⁻²⁴eV in the Starobinsky model, corresponding to the lowest frequency of 10⁻⁹ Hz, which may be detected by the current and future gravitational wave probes in space.