Package-X: A Mathematica package for the analytic calculation of one-loop integrals

Package-X, a Mathematica package for the analytic computation of one-loop integrals dimensionally regulated near 4 spacetime dimensions is described. Package-X computes arbitrarily high rank tensor integrals with up to three propagators, and gives compact expressions of UV divergent, IR divergent, and finite parts for any kinematic configuration involving real-valued external invariants and internal masses. Output expressions can be readily evaluated numerically and manipulated symbolically with built-in Mathematica functions. Emphasis is on evaluation speed, on readability of results, and especially on user-friendliness. Also included is a routine to compute traces of products of Dirac matrices, and a collection of projectors to facilitate the computation of fermion form factors at one-loop. The package is intended to be used both as a research tool and as an educational tool.Comment: Package files are available at http://packagex.hepforge.or

Leptobaryons as Majorana Dark Matter

We explore the dark matter and collider phenomenology of the minimal gauged $U(1)_B$ model, consisting of a leptophobic $Z_B$ gauge boson, and an accompanying Higgs $S_B$. By requirement of anomaly cancellation, the fermion sector naturally contains a dark matter candidate---a Majorana isosinglet $\chi$ stabilized by an inherent $Z_2$ symmetry. The absence of evidence for $Z$ prime dijet resonances at the LHC suggests that the scale of symmetry breaking $\Lambda_{B}\gtrsim 500$ GeV. Saturation of dark matter abundance together with limits on the direct detection cross section (dominated by Higgs exchange) constrains the Higgs mixing angle to $|\theta|\lesssim 0.22$. For small mixing angles of $|\theta| \lesssim 10^{-3}$, the $\mathcal{O}(10\%)$ branching fractions of the fermion loop-mediated $S_B\rightarrow\gamma \gamma$, $Z\gamma$, $ZZ$ modes may provide clues about the fermion content of the model at the LHC.Comment: 15 pages, 10 figures; v3: corrected typos, to appear in PR

The Electroweak Vacuum Angle

We reveal a new source of CP-violation in the electroweak sector that is free of any experimental bounds, and we highlight the possible implications for baryogenesis.Comment: to appear in Physics Letters

Baryon Asymmetry, Dark Matter and Local Baryon Number

We propose a new mechanism to understand the relation between the baryon and dark matter asymmetries in the universe in theories where the baryon number is a local symmetry. In these scenarios the B-L asymmetry generated through a mechanism such as leptogenesis is transferred to the dark matter and baryonic sectors through sphalerons processes which conserve total baryon number. We show that it is possible to have a consistent relation between the dark matter relic density and the baryon asymmetry in the universe even if the baryon number is broken at the low scale through the Higgs mechanism. We also discuss the case where one uses the Stueckelberg mechanism to understand the conservation of baryon number in nature.Comment: to appear in Physics Letters

Electroweak Absolute, Meta-, and Thermal Stability in Neutrino Mass Models

We analyze the stability of the electroweak vacuum in neutrino mass models containing right handed neutrinos or fermionic isotriplets. In addition to considering absolute stability, we place limits on the Yukawa couplings of new fermions based on metastability and thermal stability in the early Universe. Our results reveal that the upper limits on the neutrino Yukawa couplings can change significantly when the top quark mass is allowed to vary within the experimental range of uncertainty in its determination.Comment: 7 pages, 4 figures, match published versio

Minimal Theory for Lepto-Baryons

We investigate the simplest models where baryon and lepton numbers are defined as local symmetries spontaneously broken at the low scale and discuss the implications for cosmology. We define the simplest anomaly-free theory for spontaneous baryon and lepton number violation which predicts the existence of lepto-baryons. In this context we study the new sphaleron condition on the chemical potentials and show the relation between the present baryon asymmetry and the B-L asymmetry generated in the early universe. The properties of the cold dark matter candidate for which stability is a natural consequence from symmetry breaking are briefly discussed.Comment: to appear in Physics Letters

Implications for Electric Dipole Moments of a Leptoquark Scenario for the BB-Physics Anomalies

Vector leptoquarks can address the lepton flavor universality anomalies in decays associated with the $b \to c \ell \nu$ and $b \to s \ell \ell$ transitions, as observed in recent years. Generically, these leptoquarks yield new sources of CP violation. In this paper, we explore constraints and discovery potential for electric dipole moments (EDMs) in leptonic and hadronic systems. We provide the most generic expressions for dipole moments induced by vector leptoquarks at one loop. We find that $O(1)$ CP-violating phases in tau and muon couplings can lead to corresponding EDMs within reach of next-generation EDM experiments, and that existing bounds on the electron EDM already put stringent constraints on CP-violating electron couplings

Stepping into electroweak symmetry breaking: Phase transitions and Higgs phenomenology

We study the dynamics of electroweak symmetry breaking in an extension of the Standard Model where the Higgs sector is augmented by the addition of a real (Y=0) isospin triplet. We show that this scenario exhibits a novel, two-step electroweak phase transition, wherein the first step provides the strongly first-order transition as required for electroweak baryogenesis, followed by a second step to the Standard Model Higgs phase that also admits a cold dark matter candidate. We analyze the constraints on this scenario from recent results obtained at the Large Hadron Collider for the Higgs diphoton decay channel. We argue that this two-step scenario can be generalized to extensions of the Standard Model with additional higher-dimensional scalar multiplets that may yield realistic baryogenesis dynamics