arXiv subjects

Jonathan Kozaczuk

Publications and source records attributed to Jonathan Kozaczuk.

35 records · Page 2Linked to original sources

arXiv2017

Light Axial Vectors, Nuclear Transitions, and the $^8$Be Anomaly

New hidden particles could potentially be emitted and discovered in rare nuclear transitions. In this work we investigate the production of hidden vector bosons with primarily axial couplings to light quarks in nuclear transitions, and we apply our results to the recent anomaly seen in $^8$Be decays. The relevant matrix elements for $^8{\rm Be}^*(1^+) \rightarrow ^8{\rm Be} (0^+)$ transitions are calculated using ${\it ab \, initio}$ methods with inter-nucleon forces derived from chiral effective field theory and the in-medium similarity renormalization group. We find that the emission of a light axial vector with mass $m_X \simeq 17\, {\rm MeV}$ can account for the anomaly seen in the $1^+\to 0^+$ isoscalar transition together with the absence of a significant anomaly in the corresponding isovector transition. We also show that such an axial vector can be derived from an anomaly-free ultraviolet-complete theory that is consistent with current experimental data.

hep-ph↗

arXiv2017

Transplanckian Censorship and Global Cosmic Strings

Large field excursions are required in a number of axion models of inflation. These models also possess global cosmic strings, around which the axion follows a path mirroring the inflationary trajectory. Cosmic strings are thus an interesting theoretical laboratory for the study of transplanckian field excursions. We describe connections between various effective field theory models of axion monodromy and study the classical spacetimes around their supercritical cosmic strings. For small decay constants $f M_p/f$, the EFT is under control and the string cores undergo topological inflation, which may be either of exponential or power-law type. We show that the exterior spacetime is nonsingular and equivalent to a decompactifying cigar geometry, with the radion rolling in a potential generated by axion flux. Signals are able to circumnavigate infinite straight strings in finite but exponentially long time, $t\sim e^{Δa/M_p}$. For finite loops of supercritical string in asymptotically flat space, we argue that if topological inflation occurs, then topological censorship implies transplanckian censorship, or that external observers are forbidden from threading the loop and observing the full excursion of the axion.

hep-th↗

arXiv2017

Non-resonant Collider Signatures of a Singlet-Driven Electroweak Phase Transition

We analyze the collider signatures of the real singlet extension of the Standard Model in regions consistent with a strong first-order electroweak phase transition and a singlet-like scalar heavier than the Standard Model-like Higgs. A definitive correlation exists between the strength of the phase transition and the trilinear coupling of the Higgs to two singlet-like scalars, and hence between the phase transition and non-resonant scalar pair production involving the singlet at colliders. We study the prospects for observing these processes at the LHC and a future 100 TeV $pp$ collider, focusing particularly on double singlet production. We also discuss correlations between the strength of the electroweak phase transition and other observables at hadron and future lepton colliders. Searches for non-resonant singlet-like scalar pair production at 100 TeV would provide a sensitive probe of the electroweak phase transition in this model, complementing resonant di-Higgs searches and precision measurements. Our study illustrates a strategy for systematically exploring the phenomenologically viable parameter space of this model, which we hope will be useful for future work.

hep-ph↗

arXiv2016

The Higgs Portal and Cosmology

Higgs portal interactions provide a simple mechanism for addressing two open problems in cosmology: dark matter and the baryon asymmetry. In the latter instance, Higgs portal interactions may contain the ingredients for a strong first order electroweak phase transition as well as new CP-violating interactions as needed for electroweak baryogenesis. These interactions may also allow for a viable dark matter candidate. We survey the opportunities for probing the Higgs portal as it relates to these questions in cosmology at the LHC and possible future colliders.

hep-ph↗

arXiv2016

Science with the space-based interferometer eLISA. II: Gravitational waves from cosmological phase transitions

We investigate the potential for the eLISA space-based interferometer to detect the stochastic gravitational wave background produced by strong first-order cosmological phase transitions. We discuss the resulting contributions from bubble collisions, magnetohydrodynamic turbulence, and sound waves to the stochastic background, and estimate the total corresponding signal predicted in gravitational waves. The projected sensitivity of eLISA to cosmological phase transitions is computed in a model-independent way for various detector designs and configurations. By applying these results to several specific models, we demonstrate that eLISA is able to probe many well-motivated scenarios beyond the Standard Model of particle physics predicting strong first-order cosmological phase transitions in the early Universe.

astro-ph.CO↗

arXiv2016

Compressing the Inert Doublet Model

The Inert Doublet Model relies on a discrete symmetry to prevent couplings of the new scalars to Standard Model fermions. This stabilizes the lightest inert state, which can then contribute to the observed dark matter density. In the presence of additional approximate symmetries, the resulting spectrum of exotic scalars can be compressed. Here, we study the phenomenological and cosmological implications of this scenario. We derive new limits on the compressed Inert Doublet Model from LEP, and outline the prospects for exclusion and discovery of this model at dark matter experiments, the LHC, and future colliders.

hep-ph↗

arXiv2015

Bubble Expansion and the Viability of Singlet-Driven Electroweak Baryogenesis

The standard picture of electroweak baryogenesis requires slowly expanding bubbles. This can be difficult to achieve if the vacuum expectation value of a gauge singlet scalar field changes appreciably during the electroweak phase transition. It is important to determine the bubble wall velocity in this case, since the predicted baryon asymmetry can depend sensitively on its value. Here, this calculation is discussed and illustrated in the real singlet extension of the Standard Model. The friction on the bubble wall is computed using a kinetic theory approach and including hydrodynamic effects. Wall velocities are found to be rather large ($v_w \gtrsim 0.2$) but compatible with electroweak baryogenesis in some portions of the parameter space. If the phase transition is strong enough, however, a subsonic solution may not exist, precluding non-local electroweak baryogenesis altogether. The results presented here can be used in calculating the baryon asymmetry in various singlet-driven scenarios, as well as other features related to cosmological phase transitions in the early Universe, such as the resulting spectrum of gravitational radiation.

hep-ph↗

arXiv2015

Electroweak Baryogenesis from Exotic Electroweak Symmetry Breaking

We investigate scenarios in which electroweak baryogenesis can occur during an exotic stage of electroweak symmetry breaking in the early Universe. This transition is driven by the expectation value of a new electroweak scalar instead of the standard Higgs field. A later, second transition then takes the system to the usual electroweak minimum, dominated by the Higgs, while preserving the baryon asymmetry created in the first transition. We discuss the general requirements for such a two-stage electroweak transition to be suitable for electroweak baryogenesis and present a toy model that illustrates the necessary ingredients. We then apply these results to construct an explicit realization of this scenario within the inert two Higgs doublet model. Despite decoupling the Higgs from the symmetry-breaking transition required for electroweak baryogenesis, we find that this picture generically predicts new light states that are accessible experimentally.

hep-ph↗

arXiv2015

Cosmological Phase Transitions and their Properties in the NMSSM

We study cosmological phase transitions in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) in light of the Higgs discovery. We use an effective field theory approach to calculate the finite temperature effective potential, focusing on regions with significant tree-level contributions to the Higgs mass, a viable neutralino dark matter candidate, 1-2 TeV stops, and with the remaining particle spectrum compatible with current LHC searches and results. The phase transition structure in viable regions of parameter space exhibits a rich phenomenology, potentially giving rise to one- or two-step first-order phase transitions in the singlet and/or $SU(2)$ directions. We compute several parameters pertaining to the bubble wall profile, including the bubble wall width and $Δβ$ (the variation of the ratio in Higgs vacuum expectation values across the wall). These quantities can vary significantly across small regions of parameter space and can be promising for successful electroweak baryogenesis. We estimate the wall velocity microphysically, taking into account the various sources of friction acting on the expanding bubble wall. Ultra-relativistic solutions to the bubble wall equations of motion typically exist when the electroweak phase transition features substantial supercooling. For somewhat weaker transitions, the bubble wall instead tends to be sub-luminal and, in fact, likely sub-sonic, suggesting that successful electroweak baryogenesis may indeed occur in regions of the NMSSM compatible with the Higgs discovery.

hep-ph↗

arXiv2015

Confronting the Moduli-Induced LSP Problem

Moduli fields with Planck-suppressed couplings to light species are common in string compactifications. Decays of these moduli can reheat the universe at a late time and produce dark matter non-thermally. For generic moduli fields motivated by string theory with masses similar to that of the gravitino and TeV-scale superpartners in the minimal supersymmetric Standard Model (MSSM), the non-thermal production of the lightest superpartner (LSP) tends to create an unacceptably large relic density or too strong of an indirect detection signal. We call this the moduli-induced LSP problem of the MSSM. In this paper we investigate extensions of the MSSM containing new LSP candidates that can alleviate this tension. We examine the viability of this scenario in models with light Abelian and non-Abelian hidden sectors, and symmetric or asymmetric dark matter. In these extensions it is possible, though somewhat challenging, to avoid a moduli-induced LSP problem. In all but the asymmetric scenario, the LSP can account for only a small fraction of the observed dark matter density.

hep-ph↗

arXiv2015

Extending LHC Coverage to Light Pseudoscalar Mediators and Coy Dark Sectors

Many dark matter models involving weakly interacting massive particles (WIMPs) feature new, relatively light pseudoscalars that mediate dark matter pair annihilation into Standard Model fermions. In particular, simple models of this type can explain the gamma ray excess originating in the Galactic Center as observed by the Fermi Large Area Telescope. In many cases the pseudoscalar's branching ratio into WIMPs is suppressed, making these states challenging to detect at colliders through standard dark matter searches. Here, we study the prospects for observing these light mediator states at the LHC without exploiting missing energy techniques. While existing searches effectively probe pseudoscalars with masses between 5 - 14 GeV and above 90 GeV, the LHC reach can be extended to cover much of the interesting parameter space in the intermediate 20 - 80 GeV mass range in which the mediator can have appreciable Yukawa-like couplings to Standard Model fermions but would have escaped detection by LEP and other experiments. Models explaining the Galactic Center excess via a light pseudoscalar mediator can give rise to a promising signal in this regime through the associated production of the mediator with bottom quarks while satisfying all other existing constraints. We perform an analysis of the backgrounds and trigger efficiencies, detailing the cuts that can be used to extract the signal. A significant portion of the otherwise unconstrained parameter space of these models can be conclusively tested at the 13 TeV LHC with 100 fb$^{-1}$, and we encourage the ATLAS and CMS collaborations to extend their existing searches to this mass range.

hep-ph↗

arXiv2014

Light NMSSM Neutralino Dark Matter in the Wake of CDMS II and a 126 GeV Higgs

Recent results from the Cryogenic Dark Matter Search (CDMS) experiment have renewed interest in light dark matter with a large spin-independent neutralino-nucleon scattering cross-section. Here, we examine the regions of the Next-to-MSSM (NMSSM) capable of producing a light neutralino with a large spin-independent scattering cross-section, with the scattering mediated by a very light singlet-like scalar, and a 126 GeV Standard Model-like Higgs consistent with the LHC results, while satisfying other relevant cosmological, flavor and collider constraints. We focus on two different scenarios for annihilation in the early universe, namely annihilation mediated by (1) a light scalar or by (2) a light pseudo-scalar. As expected, both cases are highly constrained. Nevertheless, we find that there persists potentially viable parameter space to accommodate either scenario. In the first, accidental cancellations in the couplings allow for a SM-like Higgs with a total width and invisible branching fraction compatible with the observed Higgs boson. Alternatively, the second scenario can occur in regions featuring smaller branching fractions of the SM-like Higgs to pairs of light scalars, pseudoscalars, and neutralinos without cancellations. The strongest constraints in both cases come from rare meson decays and exotic decays of the SM-like Higgs boson into neutralinos and light, CP-even Higgs pairs. We outline the relevant parameter space for both scenarios and comment on prospects for future discovery with various experiments.

hep-ph↗

arXiv2013

Electroweak Baryogenesis And The Fermi Gamma-Ray Line

Many particle physics models attempt to explain the 130 GeV gamma-ray feature that the Fermi-LAT observes in the Galactic Center. Neutralino dark matter in non-minimal supersymmetric models, such as the NMSSM, is an especially well-motivated theoretical setup which can explain the line. We explore the possibility that regions of the NMSSM consistent with the 130 GeV line can also produce the observed baryon asymmetry of the universe via electroweak baryogenesis. We find that such regions can in fact accommodate a strongly first-order electroweak phase transition (due to the singlet contribution to the effective potential), while also avoiding a light stop and producing a Standard Model-like Higgs in the observed mass range. Simultaneously, CP-violation from a complex phase in the wino-higgsino sector can account for the observed baryon asymmetry through resonant sources at the electroweak phase transition, while satisfying current constraints from dark matter, collider, and electric dipole moment (EDM) experiments. This result is possible by virtue of a relatively light pseudoscalar Higgs sector with a small degree of mixing, which yields efficient s-channel resonant neutralino annihilation consistent with indirect detection constraints, and of the moderate values of $μ$ required to obtain a bino-like LSP consistent with the line. The wino mass is essentially a free parameter which one can tune to satisfy electroweak baryogenesis. Thus, the NMSSM framework can potentially explain the origins of both baryonic and dark matter components in the Universe. The tightness of the constraints we impose on this scenario makes it extraordinarily predictive, and conclusively testable in the near future by modest improvements in EDM and dark matter search experiments.

hep-ph↗

arXiv2012

Supersymmetric Electroweak Baryogenesis Via Resonant Sfermion Sources

We calculate the baryon asymmetry produced at the electroweak phase transition by quasi-degenerate third generation sfermions in the minimal supersymmetric extension of the Standard Model. We evaluate constraints from Higgs searches, from collider searches for supersymmetric particles, and from null searches for the permanent electric dipole moment (EDM) of the electron, of the neutron and of atoms. We find that resonant sfermion sources can in principle provide a large enough baryon asymmetry in various corners of the sfermion parameter space, and we focus, in particular, on the case of large $\tanβ$, where third-generation down-type (s)fermions become relevant. We show that in the case of stop and sbottom sources, the viable parameter space is ruled out by constraints from the non-observation of the Mercury EDM. We introduce a new class of CP violating sources, quasi-degenerate staus, that escapes current EDM constraints while providing large enough net chiral currents to achieve successful "slepton-mediated" electroweak baryogenesis.

hep-ph↗

arXiv2012

Accidental Supersymmetric Dark Matter and Baryogenesis

We show that "accidental" supersymmetry is a beyond-the-Standard Model framework that naturally accommodates a thermal relic dark matter candidate and successful electroweak baryogenesis, including the needed strongly first-order character of the electroweak phase transition. We study the phenomenology of this setup from the standpoint of both dark matter and baryogenesis. For energies around the electroweak phase transition temperature, the low-energy effective theory is similar to the MSSM with light super-partners of the third-generation quarks and of the Higgs and gauge bosons. We calculate the dark matter relic abundance and the baryon asymmetry across the accidental supersymmetry parameter space, including resonant and non-resonant CP-violating sources. We find that there are regions of parameter space producing both the observed value of the baryon asymmetry and a dark matter candidate with the correct relic density and conforming to present-day constraints from dark matter searches. This scenario makes sharp predictions for the particle spectrum, predicting a lightest neutralino mass between 200 and 500 GeV, with all charginos and neutralinos within less than a factor 2 of the lightest neutralino mass and the heavy Higgs sector within 20-25% of that mass, making it an interesting target for collider searches. In addition, we demonstrate that successful accidental supersymmetric dark matter and baryogenesis will be conclusively tested with improvements smaller than one order of magnitude to the current performance of electron electric dipole moment searches and of direct dark matter searches, as well as with IceCube plus Deep Core neutrino telescope data.

hep-ph↗

arXiv2012

Multiple Cosmic Collisions and the Microwave Background Power Spectrum

Collisions between cosmic bubbles of different vacua are a generic feature of false vacuum eternal inflation scenarios. While previous studies have focused on the consequences of a single collision event in an observer's past, we begin here an investigation of the more general scenario allowing for many "mild" collisions intersecting our past light cone (and one another). We discuss the general features of multiple collision scenarios and consider their impact on the cosmic microwave background (CMB) temperature power spectrum, treating the collisions perturbatively. In a large class of models, one can approximate a multiple collision scenario as a superposition of individual collision events governed by nearly isotropic and scale-invariant distributions, most appearing to take up less than half of the sky. In this case, the shape of the expected CMB temperature spectrum maintains statistical isotropy and typically features a dramatic increase in power in the low multipoles relative to that of the best-fit $Λ$CDM model, which is in tension particularly with the observed quadrupole. We argue that this predicted spectrum is largely model-independent and can be used to outline features of the underlying statistical distributions of colliding bubbles consistent with CMB temperature measurements.

hep-th↗

arXiv2011

Closing in on Supersymmetric Electroweak Baryogenesis with Dark Matter Searches and the Large Hadron Collider

We study the impact of recent direct and indirect searches for particle dark matter on supersymmetric models with resonant neutralino- or chargino-driven electroweak baryogenesis (EWB) and heavy sfermions. We outline regions of successful EWB on the planes defined by gaugino and higgsino mass parameters, and calculate the portions of those planes excluded by dark matter search results, and the regions soon to be probed by current and future experiments. We conclude that dark matter searches robustly exclude a wino-like lightest supersymmetric particle in successful EWB regions. Bino-like dark matter is still a possibility, although one that will be probed with a modest improvement in the sensitivity of current direct and indirect detection experiments. We also calculate the total production cross section of chargino and neutralino pairs at the Large Hadron Collider, with a center of mass energy of 7 and 14 TeV.

hep-ph↗