Nonexponential decay of an unstable quantum system: Small-QQ-value s-wave decay

We study the decay process of an unstable quantum system, especially the deviation from the exponential decay law. We show that the exponential period no longer exists in the case of the s-wave decay with small $Q$ value, where the $Q$ value is the difference between the energy of the initially prepared state and the minimum energy of the continuous eigenstates in the system. We also derive the quantitative condition that this kind of decay process takes place and discuss what kind of system is suitable to observe the decay.Comment: 17 pages, 6 figure

Entropy production by Q-ball decay for diluting long-lived charged particles

The cosmic abundance of a long-lived charged particle such as a stau is tightly constrained by the catalyzed big bang nucleosynthesis. One of the ways to evade the constraints is to dilute those particles by a huge entropy production. We evaluate the dilution factor in a case that non-relativistic matter dominates the energy density of the universe and decays with large entropy production. We find that large Q balls can do the job, which is naturally produced in the gauge-mediated supersymmetry breaking scenario.Comment: 8 pages, 1 figur

Bounds on long-lived charged massive particles from Big Bang nucleosynthesis

The Big Bang nucleosynthesis (BBN) in the presence of charged massive particles (CHAMPs) is studied in detail. All currently known effects due to the existence of bound states between CHAMPs and nuclei, including possible late-time destruction of Li6 and Li7 are included. The study sets conservative bounds on CHAMP abundances in the decay time range 3x10^2 sec - 10^12 sec. It is stressed that the production of Li6 at early times T ~ 10keV is overestimated by a factor ~ 10 when the approximation of the Saha equation for the He4 bound state fraction is utilised. To obtain conservative limits on the abundance of CHAMPs, a Monte-Carlo analysis with ~ 3x10^6 independent BBN runs, varying reaction rates of nineteen different reactions, is performed (see attached erratum, however). The analysis yields the surprising result that except for small areas in the particle parameter space conservative constraints on the abundance of decaying charged particles are currently very close to those of neutral particles. It is shown that, in case a number of heretofore unconsidered reactions may be determined reliably in future, it is conceivable that the limit on CHAMPs in the early Universe could be tightened by orders of magnitude. An ERRATUM gives limits on primordial CHAMP densities when the by Ref. Kamimura et al. recently more accurately determined CHAMP reaction rates are employed.Comment: includes Erratum showing most up to date limits after determination of the most important reaction rate

A Bitter Pill: The Primordial Lithium Problem Worsens

The lithium problem arises from the significant discrepancy between the primordial 7Li abundance as predicted by BBN theory and the WMAP baryon density, and the pre-Galactic lithium abundance inferred from observations of metal-poor (Population II) stars. This problem has loomed for the past decade, with a persistent discrepancy of a factor of 2--3 in 7Li/H. Recent developments have sharpened all aspects of the Li problem. Namely: (1) BBN theory predictions have sharpened due to new nuclear data, particularly the uncertainty on 3He(alpha,gamma)7Be, has reduced to 7.4%, and with a central value shift of ~ +0.04 keV barn. (2) The WMAP 5-year data now yields a cosmic baryon density with an uncertainty reduced to 2.7%. (3) Observations of metal-poor stars have tested for systematic effects, and have reaped new lithium isotopic data. With these, we now find that the BBN+WMAP predicts 7Li/H = (5.24+0.71-0.67) 10^{-10}. The Li problem remains and indeed is exacerbated; the discrepancy is now a factor 2.4--4.3 or 4.2sigma (from globular cluster stars) to 5.3sigma (from halo field stars). Possible resolutions to the lithium problem are briefly reviewed, and key nuclear, particle, and astronomical measurements highlighted.Comment: 21 pages, 4 figures. Comments welcom

A 119-125 GeV Higgs from a string derived slice of the CMSSM

The recent experimental hints for a relatively heavy Higgs with a mass in the range 119-125 GeV favour supersymmetric scenarios with a large mixing in the stop mass matrix. It has been shown that this is possible in the constrained Minimal Super-symmetric Standard Model (CMSSM), but only for a very specific relation between the trilinear parameter and the soft scalar mass, favouring A ≈ −2m for a relatively light spectrum, and sizable values of tan β. We describe here a string-derived scheme in which the first condition is automatic and the second arises as a consequence of imposing radiative EW symmetry breaking and viable neutralino dark matter in agreement with WMAP constraints. More specifically, we consider modulus dominated SUSY-breaking in Type II string compactifications and show that it leads to a very predictive CMSSM-like scheme, with small departures due to background fluxes. Imposing the above constraints leaves only one free parameter, which corresponds to an overall scale. We show that in this construction A=−3/2–√m≃−2mA=−3/2m≃−2m and in the allowed parameter space tan β ≃ 38 − 41, leading to 119 GeV < mh  < 125 GeV. The recent LHCb results on BR(Bs → μ+μ−) further constrain this range, leaving only the region with mh ~ 125. GeV. We determine the detectability of this model and show that it could start being probed by the LHC at 7(8) TeV with a luminosity of 5(2) fb−1, and the whole parameter space would be accessible for 14 TeV and 25 fb−1. Furthermore, this scenario can host a long-lived stau with the right properties to lead to catalyzed BBN. We finally argue that anthropic arguments could favour the highest value for the Higgs mass that is compatible with neutralino dark matter, i.e., mh-125 GeV

The New Look pMSSM with Neutralino and Gravitino LSPs

The pMSSM provides a broad perspective on SUSY phenomenology. In this paper we generate two new, very large, sets of pMSSM models with sparticle masses extending up to 4 TeV, where the lightest supersymmetric particle (LSP) is either a neutralino or gravitino. The existence of a gravitino LSP necessitates a detailed study of its cosmological effects and we find that Big Bang Nucleosynthesis places strong constraints on this scenario. Both sets are subjected to a global set of theoretical, observational and experimental constraints resulting in a sample of \sim 225k viable models for each LSP type. The characteristics of these two model sets are briefly compared. We confront the neutralino LSP model set with searches for SUSY at the 7 TeV LHC using both the missing (MET) and non-missing ET ATLAS analyses. In the MET case, we employ Monte Carlo estimates of the ratios of the SM backgrounds at 7 and 8 TeV to rescale the 7 TeV data-driven ATLAS backgrounds to 8 TeV. This allows us to determine the pMSSM parameter space coverage for this collision energy. We find that an integrated luminosity of \sim 5-20 fb^{-1} at 8 TeV would yield a substantial increase in this coverage compared to that at 7 TeV and can probe roughly half of the model set. If the pMSSM is not discovered during the 8 TeV run, then our model set will be essentially void of gluinos and lightest first and second generation squarks that are \lesssim 700-800 GeV, which is much less than the analogous mSUGRA bound. Finally, we demonstrate that non-MET SUSY searches continue to play an important role in exploring the pMSSM parameter space. These two pMSSM model sets can be used as the basis for investigations for years to come.Comment: 54 pages, 22 figures; typos fixed, references adde

Lithium in the Globular Cluster NGC 6397: Evidence for dependence on evolutionary status

Most Globular Clusters are believed to host a single stellar populations. They can thus be considered a good place to study the Spite plateau and probe for possible evolutionary modifications of the Li content. We want to determine the Li content of subgiant (SG) and Main Sequence (MS) stars of the old, metal-poor globular cluster NGC 6397. This work was aimed not only at studying possible Li abundance variations but to investigate the cosmological Li discrepancy. Here, we present FLAMES/GIRAFFE observations of a sample of 84 SG and 79 MS stars in NGC 6397 selected in a narrow range of B-V colour and, therefore, effective temperatures. We determine both Teff and A(Li) using 3D hydrodynamical model atmospheres for all the MS and SG stars of the sample. We find a significant difference in the Li abundance between SG stars and MS stars, the SG stars having an A(Li) higher by almost 0.1 dex on average. We also find a decrease in the A(Li) with decreasing Teff, both in MS and SG stars, albeit with a significantly different slope for the two classes of stars. This suggests that the lithium abundance in these stars is, indeed, altered by some process, which is Teff-dependent. The Li abundance pattern observed in NGC 6397 is different from what is found among field stars, casting some doubt on the use of Globular Cluster stars as representative of Population II with respect to the Li abundance. None of the available theories of Li depletion appears to satisfactorily describe our observations.Comment: Accepted for publication in A&A Letters; new version with few correction

Probing new physics with long-lived charged particles produced by atmospheric and astrophysical neutrinos

As suggested by some extensions of the Standard Model of particle physics, dark matter may be a super-weakly interacting lightest stable particle, while the next-to-lightest particle (NLP) is charged and meta-stable. One could test such a possibility with neutrino telescopes, by detecting the charged NLPs produced in high-energy neutrino collisions with Earth matter. We study the production of charged NLPs by both atmospheric and astrophysical neutrinos; only the latter, which is largely uncertain and has not been detected yet, was the focus of previous studies. We compute the resulting fluxes of the charged NLPs, compare those of different origins, and analyze the dependence on the underlying particle physics setup. We point out that even if the astrophysical neutrino flux is very small, atmospheric neutrinos, especially those from the prompt decay of charmed mesons, may provide a detectable flux of NLP pairs at neutrino telescopes such as IceCube. We also comment on the flux of charged NLPs expected from proton-nucleon collisions, and show that, for theoretically motivated and phenomenologically viable models, it is typically sub-dominant and below detectable rates.Comment: 27 pages, 6 figures; accepted for publication in JCA

Non-exponential decay in quantum field theory and in quantum mechanics: the case of two (or more) decay channels

We study the deviations from the exponential decay law, both in quantum field theory (QFT) and quantum mechanics (QM), for an unstable particle which can decay in (at least) two decay channels. After a review of general properties of non-exponential decay in QFT and QM, we evaluate in both cases the decay probability that the unstable particle decays in a given channel in the time interval between $t$ and $t+dt.$ An important quantity is the ratio of the probability of decay into the first and the second channel: this ratio is constant in the Breit-Wigner limit (in which the decay law is exponential) and equals the quantity $\Gamma_{1}/\Gamma_{2}$, where $\Gamma_{1}$ and $\Gamma_{2}$ are the respective tree-level decay widths. However, in the full treatment (both for QFT and QM) it is an oscillating function around the mean value $\Gamma_{1}/\Gamma_{2}$ and the deviations from this mean value can be sizable. Technically, we study the decay properties in QFT in the context of a superrenormalizable Lagrangian with scalar particles and in QM in the context of Lee Hamiltonians, which deliver formally analogous expressions to the QFT case.Comment: 32 pages, 10 figures. To appear in "Foundations of Physics