arXiv subjects

Bob McElrath

Publications and source records attributed to Bob McElrath.

At least 19 recordsLinked to original sources

arXiv2020

Bitcoin Covenants: Three Ways to Control the Future

A bitcoin covenant is a mechanism to enforce conditions on how the control of coins will be transferred in the future. This work introduces deleted-key covenants; using pre-signed transactions with secure key deletion. With this, a general class of covenants are possible without introducing new security risks to bitcoin. There is a range of security models for the key deletion process, but this is subject to a security-convenience trade-off and requires interactivity in a multi-party context. On the other hand, this work makes a compelling case for what can be gained through a soft-fork upgrade to the signature hash system [Dec17] which enables recovered-key covenants through elliptic curve key recovery. This has similar properties to script-based covenant mechanisms proposed previously [Rub20]. Key factors are discussed and compared for the three covenant mechanisms, including; the enforcement process, methods for proving accessibility of funds and whether or not they are bound by a covenant, methods for dynamic fee allocation, the underlying cryptographic assumptions, and their feasibility in single-party, hierarchical and adversarial multi-party contexts. Despite the relative downsides of deleted-key covenants, they are a practical tool for custody protocol design. The comparison shows precisely how soft-fork proposals improve the practicality of bitcoin covenants, through non-interactive enforcement and tighter cryptographic assumptions, to enhance custody protocols and enable some adversarial applications such as payment protocols.

cs.CR↗

arXiv2020

Custody Protocols Using Bitcoin Vaults

A bitcoin \textit{covenant} is a mechanism to enforce conditions on future bitcoin transactions. A bitcoin \textit{vault} is a specific type of covenant transaction that enforces a time-lock on the transfer of control of funds to a hot wallet, but enables an immediate transfer of funds into a deep cold recovery wallet. This paper demonstrates how to integrate a bitcoin vault into a custody protocol and demonstrates the security properties of that protocol. The vault is implemented using pre-signed transactions with secure key deletion (as proposed in \cite{Swambo2020cov}). It is shown that vault-custody protocols enable the wallet owner to specify their desired balance for an inherent trade-off between the security of and accessibility of bitcoin holdings by adjusting the length of time-locks used. It is also demonstrated that wallet owners have increased control of risk-management by compartmentalizing funds across numerous vault transactions. While it isn't realistic to completely prevent theft, the most likely theft scenarios (compromising the hot wallet) have severely limited profitability for an attacker, deterring attempts at theft from the beginning. The proposed architecture was designed to offer defence-in-depth through redundancy and fault-tolerant functionality as well as countermeasures for class breaks through diversity across hardware and software layers. Finally, the architecture employs a detection (a watchtower) and response system that enables fail-safe recovery from attempted or partial thefts through a second type of covenant transaction, a push-to-recovery-wallet transaction.

cs.CR↗

arXiv2013

On The Origin of Neutrino Mass and Mixing in the Standard Model

One can describe cosmological relic neutrinos by adding Lagrange multipliers to the Standard Model Lagrangian for them. The two possible Lagrange multipliers are a chemical potential, which fixes the mean neutrino/anti-neutrino asymmetry, and a Majorana mass, which fixes the mean spin-entropy. Because these neutrinos originated from a thermal bath, their entropy should be maximal, implying that each state in the background is a symmetric superposition of a neutrino and anti-neutrino. Therefore the Standard Model must be augmented by a flavor-diagonal Majorana neutrino mass matrix. This impacts the propagator via tadpole diagrams due to self-interactions. In the low-energy limit, neutrino self-interactions are entirely off-diagonal because same-flavor four-fermion operators vanish by Pauli exclusion. These interactions must be diagonalized when propagating through a bath of neutrinos, using the U(3) global flavor symmetry. U(3) gets broken broken down to SO(3) by Majorana masses, and down to $A_4$ if the three masses are different. Thus our universe today contains tri-bimaximal mixing and Majorana neutrinos. Neutrino mixing is due to the mismatch between the flavor-diagonal Majorana mass matrix arising at finite density and the self-interaction diagonal finite density propagator. The mass hierarchy is inverted and Majorana phases are absent. Lepton number is conserved and the neutrino-less double beta decay experiment absorbs a pair of neutrinos from the relic background and will prove their Majorana nature.

hep-ph↗

arXiv2010

Accurate Mass Determinations in Decay Chains with Missing Energy: II

We discuss kinematic methods for determining the masses of the particles in events at a hadron collider in which a pair of identical particles is produced with each decaying via a series of on-shell intermediate beyond-the-SM (BSM) particles to visible SM particles and an invisible particle (schematically, pp -> ZZ + jets with Z -> Aa -> Bba -> Ccba -> ... -> cba... + N where a,b,c,... are visible SM particles or groups of SM particles, A,B,C,... are on-shell BSM particles and N is invisible). This topology arises in many models including SUSY processes such as squark and gluino pair production and decay. We present the detailed procedure for the case of Z -> 3 visible particles + N and demonstrate that the masses obtained from the kinematic procedure are independent of the model by comparing SUSY to UED.

hep-ph↗

arXiv2009

Gaugephobic Higgs Signals at the LHC

The Gaugephobic Higgs model provides an interpolation between three different models of electroweak symmetry breaking: Higgsless models, Randall-Sundrum models, and the Standard Model. At parameter points between the extremes, Standard Model Higgs signals are present at reduced rates, and Higgsless Kaluza-Klein excitations are present with shifted masses and couplings, as well as signals from exotic quarks necessary to protect the Zbb coupling. Using a new implementation of the model in SHERPA, we show the LHC signals which differentiate the generic Gaugephobic Higgs model from its limiting cases. These are all signals involving a Higgs coupling to a Kaluza-Klein gauge boson or quark. We identify the clean signal $p p \to W^(i) \to W H$ mediated by a Kaluza-Klein W, which can be present at large rates and is enhanced for even Kaluza-Klein numbers. Due to the very hard lepton coming from the W decay, this signature has little background, and provides a better discovery channel for the Higgs than any of the Standard Model modes, over its entire mass range. A Higgs radiated from new heavy quarks also has large rates, but is much less promising due to very high multiplicity final states.

hep-ph↗

arXiv2009

Measuring neutrino mass with radioactive ions in a storage ring

We propose a method to measure the neutrino mass kinematically using beams of ions which undergo beta decay. The idea is to tune the ion beam momentum so that in most decays, the electron is forward moving with respect to the beam, and only in decays near the endpoint is the electron moving backwards. Then, by counting the backward moving electrons one can observe the effect of neutrino mass on the beta spectrum close to the endpoint. In order to reach sensitivities for $m_ν< 0.2$ eV, it is necessary to control the ion momentum with a precision better than $δp/p < 10^{-5}$, identify suitable nuclei with low Q-values (in the few to ten keV range), and one must be able to observe at least O($10^{18}$) decays.

hep-ph↗

arXiv2009

Laboratory tests for the cosmic neutrino background using beta-decaying nuclei

We point out that the Pauli blocking of neutrinos by cosmological relic neutrinos can be a significant effect. For zero-energy neutrinos, the standard parameters for the neutrino background temperature and density give a suppression of approximately 1/2. We show the effect this has on three-body beta decays. The size of the effect is of the same order as the recently suggested neutrino capture on beta-decaying nuclei.

hep-ph↗

arXiv2008

Emergent Electroweak Gravity

We show that any massive cosmological relic particle with small self-interactions is a super-fluid today, due to the broadening of its wave packet, and lack of any elastic scattering. The WIMP dark matter picture is only consistent its mass $M \gg M_{\rm Pl}$ in order to maintain classicality. The dynamics of a super-fluid are given by the excitation spectrum of bound state quasi-particles, rather than the center of mass motion of constituent particles. If this relic is a fermion with a repulsive interaction mediated by a heavy boson, such as neutrinos interacting via the $Z^0$, the condensate has the same quantum numbers as the vierbein of General Relativity. Because there exists an enhanced global symmetry $SO(3,1)_{space}\times SO(3,1)_{spin}$ among the fermion's self-interactions broken only by its kinetic term, the long wavelength fluctuation around this condensate is a Goldstone graviton. A gravitational theory exists in the low energy limit of the Standard Model's Electroweak sector below the weak scale, with a strength that is parametrically similar to $G_N$.

gr-qc↗

arXiv2008

There is no explosion risk associated with superfluid Helium in the LHC cooling system

We evaluate speculation about the possibility of a dangerous release of energy within the liquid Helium of the Large Hadron Collider (LHC) cryogenic system due to the occurrence of a "Bose-Nova". Bose-Novae are radial bursts of rapidly moving atoms which can occur when a Bose-Einstein Condensate (BEC) undergoes a collapse due the interatomic potential being deliberately made attractive using a magnetic field close to the Feshbach resonance. Liquid 4He has a monatomic structure with s-wave electrons, zero nuclear spin, no hyperfine splitting, and as a consequence no Feshbach resonance which would allow one to change its normally repulsive interactions to be attractive. Because of this, a Bose-Nova style collapse of 4He is impossible. Additional speculations concerning cold fusion during these events are easily dismissed using the usual arguments about the Coulomb barrier at low temperatures, and are not needed to explain the Bose-Einstein condensate Bose-Nova phenomenon. We conclude that that there is no physics whatsoever which suggests that Helium could undergo any kind of unforeseen catastrophic explosion.

physics.pop-ph↗

arXiv2008

Signatures of Extra Dimensions from Upsilon Decays with a Light Gaugephobic Higgs Boson

We explore non-standard Higgs phenomenology in the Gaugephobic Higgs model in which the Higgs can be lighter than the usually quoted current experimental bound. The Higgs propagates in the bulk of a 5D space-time and Electroweak Symmetry Breaking occurs by a combination of boundary conditions in the extra dimension and an elementary Higgs. The Higgs can thus have a significantly suppressed coupling to the other Standard Model fields. A large enough suppression can be found to escape all limits and allow for a Higgs of any mass, which would be associated with the discovery of W' and Z' Kaluza-Klein resonances at the LHC. The Higgs can be precisely discovered at B-factories while the LHC would be insensitive to it due to high backgrounds. In this letter we study the Higgs discovery mode in Upsilon(3S), Upsilon(2S), and Upsilon(1S) decays, and the model parameter space that will be probed by BaBar, Belle, and CLEO data. In the absence of an early discovery of a heavy Higgs at the LHC, A Super-B factory would be an excellent option to further probe this region.

hep-ph↗

arXiv2008

Accurate Mass Determinations in Decay Chains with Missing Energy

Many beyond the Standard Model theories include a stable dark matter candidate that yields missing / invisible energy in collider detectors. If observed at the Large Hadron Collider, we must determine if its mass and other properties (and those of its partners) predict the correct dark matter relic density. We give a new procedure for determining its mass with small error.

hep-ph↗

arXiv2007

Mass Determination in SUSY-like Events with Missing Energy

We describe a kinematic method which is capable of determining the overall mass scale in SUSY-like events at a hadron collider with two missing (dark matter) particles. We focus on the kinematic topology in which a pair of identical particles is produced with each decaying to two leptons and an invisible particle (schematically, $pp\to YY+jets$ followed by each $Y$ decaying via $Y\to \ell X\to \ell\ell'N$ where $N$ is invisible). This topology arises in many SUSY processes such as squark and gluino production and decay, not to mention $t\anti t$ di-lepton decays. In the example where the final state leptons are all muons, our errors on the masses of the particles $Y$, $X$ and $N$ in the decay chain range from 4 GeV for 2000 events after cuts to 13 GeV for 400 events after cuts. Errors for mass differences are much smaller. Our ability to determine masses comes from considering all the kinematic information in the event, including the missing momentum, in conjunction with the quadratic constraints that arise from the $Y$, $X$ and $N$ mass-shell conditions. Realistic missing momentum and lepton momenta uncertainties are included in the analysis.

hep-ph↗

arXiv2007

Light Higgses and Dark Matter at Bottom and Charm Factories

Neither Dark Matter nor scalar particles in the Higgs sector are ruled out at energies accessible to bottom and charm factories. In Dark Matter searches, the error on the mass of Dark Matter is $\sim 4$ GeV in the best LHC studies. For light Dark Matter this could represent a 100% (or more) error. In Higgs searches, the presence of a light singlet Higgs can make the LHC Higgs search difficult, if not impossible. If Dark Matter or a Higgs scalar is light, it will {\it require} a low-energy machine to precisely determine the couplings. We review the models, modes of discovery and rate expectations for these new particle searches at bottom and charm factories. We also discuss the options for new runs at bottom and charm factories relevant for these searches.

hep-ph↗

arXiv2006

Probing NMSSM Scenarios with Minimal Fine-Tuning by Searching for Decays of the Upsilon to a Light CP-Odd Higgs Boson

Completely natural electroweak symmetry breaking is easily achieved in supersymmetric models if there is a SM-like Higgs boson, $h$, with $m_h\lsim 100\gev$. In the minimal supersymmetric model, such an $h$ decays mainly to $b\anti b$ and is ruled out by LEP constraints. However, if the MSSM Higgs sector is expanded so that $h$ decays mainly to still lighter Higgs bosons, e.g. $h\to aa$, with $BR(h\to aa)>0.7$, and if $m_a<2m_b$, then the LEP constraints are satisfied. In this letter, we show that in the next-to-minimal supersymmetric model the above $h$ and $a$ properties (for the lightest CP-even and CP-odd Higgs bosons, respectively) imply a lower bound on $BR(Υ\to \gam a)$ that dedicated runs at present (and future) $B$ factories can explore.

hep-ph↗

arXiv2005

Light Neutralino Dark Matter in the NMSSM

Neutralino dark matter is generally assumed to be relatively heavy, with a mass near the electroweak scale. This does not necessarily need to be the case, however. In the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and other supersymmetric models with an extended Higgs sector, a very light CP-odd Higgs boson can naturally arise making it possible for a very light neutralino to annihilate efficiently enough to avoid being overproduced in the early Universe. In this article, we explore the characteristics of a supersymmetric model needed to include a very light neutralino, 100 MeV $< \mcnone <$ 20 GeV, using the NMSSM as a prototype. We discuss the most important constraints from Upsilon decays, $b \to s γ$, $B_s \to μ^+ μ^-$ and the magnetic moment of the muon, and find that a light bino or singlino neutralino is allowed, and can be generated with the appropriate relic density. It has previously been shown that the positive detection of dark matter claimed by the DAMA collaboration can be reconciled with other direct dark matter experiments such as CDMS II if the dark matter particle is rather light, between about 6 and 9 GeV. A singlino or bino-like neutralino could easily fall within this range of masses within the NMSSM. Additionally, models with sub-GeV neutralinos may be capable of generating the 511 keV gamma-ray emission observed from the galactic bulge by the INTEGRAL/SPI experiment. We also point out measurements which can be performed immediately at CLEO, BaBar and Belle using existing data to discover or significantly constrain this scenario.

hep-ph↗

arXiv2005

Invisible Quarkonium Decays as a Sensitive Probe of Dark Matter

We examine in a model-independent manner the measurements that can be performed at B-factories with sensitivity to dark matter. If a singlet scalar, pseudo-scalar, or vector is present and mediates the Standard Model - dark matter interaction, it can mediate invisible decays of quarkonium states such as the $Υ$, $J/Ψ$, and $η$. Such scenarios have arisen in the context of supersymmetry, extended Higgs sectors, solutions the supersymmetric $μ$ problem, and extra U(1) gauge groups from grand unified theories and string theory. Existing B-factories running at the $Υ(4S)$ can produce lower $Υ$ resonances by emitting an Initial State Radiation (ISR) photon. Using a combination of ISR and radiative decays, the initial state of an invisibly decaying quarkonium resonance can be tagged, giving sensitivity to the spin and CP-nature of the particle that mediates standard model-dark matter interactions. These measurements can discover or place strong constraints on dark matter scenarios where the dark matter is approximately lighter than the $b$-quark. For the decay chains $Υ(nS) \to π^+ π^- Υ(1S)$ (n=2,3) we analyze the dominant backgrounds and determine that with $400 fb^{-1}$ collected at the $Υ(4S)$, the B-factories can limit $BR(Υ(1S) \to invisible) \lsim 0.1%$.

hep-ph↗

arXiv2004

Loop induced decays of the Little Higgs: H --> gg, gamma gamma

We analyze the loop induced decays of the Higgs boson into pairs of gluons and photons in the Littlest Higgs model. We find that the deviation of the partial widths for these decays relative to their Standard Model values scales with 1/f^2, where f ~ TeV is the mass scale of the new heavy particles in the model. For f = 1 TeV, Gamma(H -> gg) is reduced by 6-10% and Gamma(H -> gamma gamma) is reduced by 5-7% compared to their Standard Model values. While the LHC and a linear e+e- collider would be sensitive to these deviations only for relatively low values of f <~ 650 GeV, a photon collider could probe the deviation in Gamma(H -> gamma gamma) up to f <~ 1.1 (0.7) TeV at the 2 (5) sigma level.

hep-ph↗

arXiv2004

The Higgs Sector in a $U(1)^\prime$ Extension of the MSSM

We consider the Higgs sector in an extension of the MSSM with extra SM singlets, involving an extra $U(1)^\prime$ gauge symmetry, in which the domain-wall problem is avoided and the effective $μ$ parameter is decoupled from the new gauge boson $Z^\prime$ mass. The model involves a rich Higgs structure very different from that of the MSSM. In particular, there are large mixings between Higgs doublets and the SM singlets, significantly affecting the Higgs spectrum, production cross sections, decay modes, existing exclusion limits, and allowed parameter range. Scalars considerably lighter than the LEP2 bound (114 GeV) are allowed, and the range $\tan β\sim 1$ is both allowed and theoretically favored. Phenomenologically, we concentrate our study on the lighter (least model-dependent, yet characteristic) Higgs particles with significant SU(2)-doublet components to their wave functions, for the case of no explicit CP violation in the Higgs sector. We consider their spectra, including the dominant radiative corrections to their masses from the top/stop loop. We computed their production cross sections and reexamine the existing exclusion limits at LEP2. We outline the searching strategy for some representative scenarios at a future linear collider. We emphasize that gaugino, Higgsino, and singlino decay modes are indicative of extended models and have been given little attention. We present a comprehensive list of model scenarios in the Appendices.

hep-ph↗