The windows for kinetically mixed Z'-mediated dark matter and the galactic center gamma ray excess

One of the simplest hidden sectors with signatures in the visible sector is fermionic dark matter $\chi$ coupled to a $Z'$ gauge boson that has purely kinetic mixing with the standard model hypercharge. We consider the combined constraints from relic density, direct detection and collider experiments on such models in which the dark matter is either a Dirac or a Majorana fermion. We point out sensitivity to details of the UV completion for the Majorana model. For kinetic mixing parameter $\epsilon \le 0.01$, only relic density and direct detection are relevant, while for larger $\epsilon$, electroweak precision, LHC dilepton, and missing energy constraints become important. We identify regions of the parameter space of $m_\chi$, $m_{Z'}$, dark gauge coupling and $\epsilon$ that are most promising for discovery through these experimental probes. We study the compatibility of the models with the galactic center gamma ray excess, finding agreement at the 2-3$\sigma$ level for the Dirac model.Comment: 13 pages, 10 figures; v.2 added reference; v.3 minor clarifications, published versio

Multimediator models for the galactic center gamma ray excess

Tentative evidence for excess GeV-scale gamma rays from the galactic center has been corroborated by several groups, including the Fermi collaboration, on whose data the observation is based. Dark matter annihilation into standard model particles has been shown to give a good fit to the signal for a variety of final state particles, but generic models are inconsistent with constraints from direct detection. Models where the dark matter annihilates to mediators that subsequently decay are less constrained. We perform global fits of such models to recent data, allowing branching fractions to all possible fermionic final states to vary. The best fit models, including constraints from the AMS-02 experiment (and also antiproton ratio), require branching primarily to muons, with a $\sim 10-20\%$ admixture of $b$ quarks, and no other species. This suggests models in which there are two scalar mediators that mix with the Higgs, and have masses consistent with such a decay pattern. The scalar that decays to $\mu^+\mu^-$ must therefore be lighter than $2m_\tau \cong 3.6$ GeV. Such a small mass can cause Sommerfeld enhancement, which is useful to explain why the best-fit annihilation cross section is larger than the value needed for a thermal relic density. For light mediator masses $\sim (0.2-2)$ GeV, it can also naturally lead to elastic DM self-interactions at the right level for addressing discrepancies in small structure formation as predicted by collisionless cold dark matter.Comment: 18 pages, 14 figures; v2: updated CMB constraint and added references; v3 corrected direct detection cross sectio

Top quark forward-backward asymmetry in R-parity violating supersymmetry

The interaction of bottom squark-mediated top quark pair production, occurring in the R-parity violating minimal supersymmetric standard model (MSSM), is proposed as an explanation of the anomalously large $t\bar{t}$ forward-backward asymmetry (FBA) observed at the Tevatron. We find that this model can give a good fit to top quark data, both the inclusive and invariant mass-dependent asymmetries, while remaining consistent (at the 2-$\sigma$ level) with the total and differential production cross-sections. The scenario is challenged by strong constraints from atomic parity violation (APV), but we point out an extra diagram for the effective down quark-Z vertex, involving the same coupling constant as required for the FBA, which tends to weaken the APV constraint, and which can nullify it for reasonable values of the top squark masses and mixing angle. Large contributions to flavor-changing neutral currents can be avoided if only the third generation of sparticles is light.Comment: 24 pages, 7 figures. v3: included LHC top production cross section data; model still consistent at 2 sigma leve

Efficacy of antibiotic prophylaxis in patients with cancer and hematopoietic stem cell transplantation recipients : A systematic review of randomized trials

PURPOSE: To determine the efficacy and safety of different prophylactic systemic antibiotics in adult and pediatric patients receiving chemotherapy or undergoing hematopoietic stem cell transplantation (HSCT). METHODS: We conducted a systematic review and performed searches of Ovid MEDLINE, MEDLINE in-process and Embase; and Cochrane Central Register of Controlled Trials. Studies were included if patients had cancer or were HSCT recipients with anticipated neutropenia, and the intervention was systemic antibacterial prophylaxis. Strategies synthesized included fluoroquinolone vs no antibiotic/nonabsorbable antibiotic; fluoroquinolone vs trimethoprim-sulfamethoxazole; trimethoprim-sulfamethoxazole vs no antibiotic; and cephalosporin vs. no antibiotic. Fluoroquinolone vs cephalosporin and levofloxacin vs ciprofloxacin were compared by network meta-analysis. Primary outcome was bacteremia. RESULTS: Of 20 984 citations screened, 113 studies comparing prophylactic antibiotic to control were included. The following were effective in reducing bacteremia: fluoroquinolone vs no antibiotic/nonabsorbable antibiotic (risk ratio (RR) 0.56, 95% confidence interval (CI) 0.41-0.76), trimethoprim-sulfamethoxazole vs no antibiotic (RR 0.59, 95% CI 0.41-0.85) and cephalosporin vs no antibiotic (RR 0.30, 95% CI 0.16-0.58). Fluoroquinolone was not significantly associated with increased Clostridium difficile infection (RR 0.62, 95% CI 0.31-1.24) or invasive fungal disease (RR 1.28, 95% CI 0.79-2.08) but did increase resistance to fluoroquinolone among bacteremia isolates (RR 3.35, 95% CI 1.12 to 10.03). Heterogeneity in fluoroquinolone effect on bacteremia was not explained by evaluated study, population, or methodological factors. Network meta-analysis revealed no direct comparisons for pre-specified analyses; superior regimens were not identified. CONCLUSIONS: Fluoroquinolone, trimethoprim-sulfamethoxazole, and cephalosporin prophylaxis reduced bacteremia. A clinical practice guideline to facilitate prophylactic antibiotic decision-making is required

Guideline for Antibacterial Prophylaxis Administration in Pediatric Cancer and Hematopoietic Stem Cell Transplantation

INTRODUCTION: Bacteremia and other invasive bacterial infections are common among children with cancer receiving intensive chemotherapy and in pediatric recipients of hematopoietic stem cell transplantation (HSCT). Systemic antibacterial prophylaxis is one approach that can be used to reduce the risk of these infections. Our purpose was to develop a clinical practice guideline (CPG) for systemic antibacterial prophylaxis administration in pediatric cancer and HSCT patients. METHODS: An international and multi-disciplinary panel was convened with representation from pediatric hematology/oncology and HSCT, pediatric infectious diseases (including antibiotic stewardship), nursing, pharmacy, a patient advocate and a CPG methodologist. The panel used the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach to generate recommendations based on the results of a systematic review of the literature. RESULTS: The systematic review identified 114 eligible randomized trials of antibiotic prophylaxis. The panel made a weak recommendation for systemic antibacterial prophylaxis for children receiving intensive chemotherapy for acute myeloid leukemia and relapsed acute lymphoblastic leukemia (ALL). Weak recommendations against the routine use of systemic antibacterial prophylaxis were made for children undergoing induction chemotherapy for ALL, autologous HSCT and allogeneic HSCT. A strong recommendation against its routine use was made for children whose therapy is not expected to result in prolonged severe neutropenia. If used, prophylaxis with levofloxacin was recommended during severe neutropenia. CONCLUSIONS: We present a CPG for systemic antibacterial prophylaxis administration in pediatric cancer and HSCT patients. Future research should evaluate the long-term effectiveness and adverse effects of prophylaxis