95 research outputs found
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
model, consisting of a leptophobic gauge boson, and an
accompanying Higgs . By requirement of anomaly cancellation, the fermion
sector naturally contains a dark matter candidate---a Majorana isosinglet
stabilized by an inherent symmetry. The absence of evidence for
prime dijet resonances at the LHC suggests that the scale of symmetry
breaking 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 . For
small mixing angles of , the
branching fractions of the fermion loop-mediated ,
, 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 -Physics Anomalies
Vector leptoquarks can address the lepton flavor universality anomalies in
decays associated with the and
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 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
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