James Unwin | Publications

My research program is dedicated to the study of physics beyond the Standard Model. In particular, currently I am especially interested in dark matter, primordial black holes, non-standard cosmological histories, and searches for new particles.

My papers both within physics as well as on other topics, are listed below in reverse chronological order by year. Note that authors on all of my publications appear alphabetically. Citations to my papers can be found on Inspire. Paper are tagged by their arXiv category and colored as follows: physics interdisciplinary .

2021

2021

hep-ph

Electroweak symmetry non-restoration from dark matter

Oleksii Matsedonskyi, James Unwin and Qingyun Wang

Journal of High Energy Physics, Dec 2021

Abs arXiv

Restoration of the electroweak symmetry at temperatures around the Higgs mass is linked to tight phenomenological constraints on many baryogenesis scenarios. A potential remedy can be found in mechanisms of electroweak symmetry non-restoration (SNR), in which symmetry breaking is extended to higher temperatures due to new states with couplings to the Standard Model. Here we show that, in the presence of a second Higgs doublet, SNR can be realized with only a handful of new fermions which can be identified as viable dark matter candidates consistent with all current observational constraints. The competing requirements on this class of models allow for SNR at temperatures up to ∼TeV, and imply the presence of sub-TeV new physics with sizable interactions with the Standard Model. As a result this scenario is highly testable with signals in reach of next-generation collider and dark matter direct detection experiments.
2021

hep-ph

Decoupling of asymmetric dark matter during an early matter dominated era

Prolay Chanda and James Unwin

Journal of Cosmology and Astroparticle Physics, Jun 2021

Abs arXiv

In models of Asymmetric Dark Matter (ADM) the relic density is set by a particle asymmetry in an analogous manner to the baryons. Here we explore the scenario in which ADM decouples from the Standard Model thermal bath during an early period of matter domination. We first present a model independent analysis for a generic ADM candidate with s-wave annihilation cross section with fairly general assumptions regarding the origin of the early matter dominated period. We contrast our results to those from conventional ADM models which assume radiation domination during decoupling. Subsequently, we examine an explicit example of this scenario in the context of an elegant SO(10) implementation of ADM in which the matter dominated era is due to a long lived heavy right-handed neutrino. In the concluding remarks we discuss the prospects for superheavy ADM in this setting.
2021

hep-ph

The First Three Seconds: a Review of Possible Expansion Histories of the Early Universe

Allahverdi al.

The Open Journal of Astrophysics, Jan 2021

Abs arXiv

It is commonly assumed that the energy density of the Universe was dominated by radiation between reheating after inflation and the onset of matter domination 54,000 years later. While the abundance of light elements indicates that the Universe was radiation dominated during Big Bang Nucleosynthesis (BBN), there is scant evidence that the Universe was radiation dominated prior to BBN. It is therefore possible that the cosmological history was more complicated, with deviations from the standard radiation domination during the earliest epochs. Indeed, several interesting proposals regarding various topics such as the generation of dark matter, matter-antimatter asymmetry, gravitational waves, primordial black holes, or microhalos during a nonstandard expansion phase have been recently made. In this paper, we review various possible causes and consequences of deviations from radiation domination in the early Universe - taking place either before or after BBN - and the constraints on them, as they have been discussed in the literature during the recent years.
2021

hep-th

On Baryogenesis from a Complex Inflaton

James Unwin

Symmetry, Dec 2021

Abs arXiv

We derive the particle asymmetry due to inflationary baryogenesis involving a complex inflaton, obtaining a different result to that in the literature. While asymmetries are found to be significantly smaller than previously calculated, in certain parameter regions baryogenesis can still be achieved.
2021

q-bio.PE

COVID-19 Forecasts via Stock Market Indicators

Yi Liang and James Unwin

Under review, Dec 2021

Abs arXiv

Reliable short term forecasting can provide potentially lifesaving insights into logistical planning, and in particular, into the optimal allocation of resources such as hospital staff and equipment. By reinterpreting COVID-19 daily cases in terms of candlesticks, we are able to apply some of the most popular stock market technical indicators to obtain predictive power over the course of the pandemics. By providing a quantitative assessment of MACD, RSI, and candlestick analyses, we show their statistical significance in making predictions for both stock market data and WHO COVID-19 data. In particular, we show the utility of this novel approach by considering the identification of the beginnings of subsequent waves of the pandemic. Finally, our new methods are used to assess whether current health policies are impacting the growth in new COVID-19 cases.

2020

2020

hep-ph

What if Planet 9 is a Primordial Black Hole?

Jakub Scholtz and James Unwin

Physical Review Letters, Jul 2020

Abs arXiv

We highlight that the anomalous orbits of Trans-Neptunian Objects (TNOs) and an excess in microlensing events in the 5-year OGLE dataset can be simultaneously explained by a new population of astrophysical bodies with mass several times that of Earth (M⊕). We take these objects to be primordial black holes (PBHs) and point out the orbits of TNOs would be altered if one of these PBHs was captured by the Solar System, inline with the Planet 9 hypothesis. Capture of a free floating planet is a leading explanation for the origin of Planet 9 and we show that the probability of capturing a PBH instead is comparable. The observational constraints on a PBH in the outer Solar System significantly differ from the case of a new ninth planet. This scenario could be confirmed through annihilation signals from the dark matter microhalo around the PBH.
2020

hep-ph

Reviving Z and Higgs mediated dark matter models in matter dominated freeze-out

Prolay Chanda, Saleh Hamdan and James Unwin

Journal of Cosmology and Astroparticle Physics, Jan 2020

Abs arXiv

It is quite conceivable that dark matter freeze-out occurred during an early period of matter domination, in which case the evolution and relic abundance differ from standard freeze-out calculations which assume a radiation dominated universe. Here we re-examine the classic models in which dark matter interactions with the Standard Model are mediated via either the Higgs or Z boson in the context of matter dominated freeze-out. We highlight that while these classic models are largely excluded by searches in the radiation dominated case, matter dominated freeze-out can relax these limits and thus revive the Higgs and Z portals. Additionally, we discuss the distinctions between matter dominated freeze-out and decoupling during the transition from matter domination to radiation domination, and we comment on the parameter regimes which lead to non-negligible dark matter production during this transition.
2020

q-bio.PE

Racial Impact on Infections and Deaths due to COVID-19 in New York City

Yunseo Choi and James Unwin

Under review, Jan 2020

Abs arXiv

Redlining is the discriminatory practice whereby institutions avoided investment in certain neighborhoods due to their demographics. Here we explore the lasting impacts of redlining on the spread of COVID-19 in New York City (NYC). Using data available through the Home Mortgage Disclosure Act, we construct a redlining index for each NYC census tract via a multi-level logistical model. We compare this redlining index with the COVID-19 statistics for each NYC Zip Code Tabulation Area. Accurate mappings of the pandemic would aid the identification of the most vulnerable areas and permit the most effective allocation of medical resources, while reducing ethnic health disparities.
2020

econ.TH

All-Pay Auctions with Different Forfeits

Benjamin Kang and James Unwin

Under review, Jan 2020

Abs arXiv

In an auction each party bids a certain amount and the one which bids the highest is the winner. Interestingly, auctions can also be used as models for other real-world systems. In an all pay auction all parties must pay a forfeit for bidding. In the most commonly studied all pay auction, parties forfeit their entire bid, and this has been considered as a model for expenditure on political campaigns. Here we consider a number of alternative forfeits which might be used as models for different real-world competitions, such as preparing bids for defense or infrastructure contracts.
2020

econ.TH

All-Pay Auctions as Models for Trade Wars and Military Annexation

Benjamin Kang and James Unwin

2019 Yau High School Awards, International Press, Jan 2020

Abs arXiv

We explore an application of all-pay auctions to model trade wars and territorial annexation. Specifically, in the model we consider the expected resource, production, and aggressive (military/tariff) power are public information, but actual resource levels are private knowledge. We consider the resource transfer at the end of such a competition which deprives the weaker country of some fraction of its original resources. In particular, we derive the quasi-equilibria strategies for two country conflicts under different scenarios. This work is relevant for the ongoing US-China trade war, and the recent Russian capture of Crimea, as well as historical and future conflicts.
2020

physics.ed-ph

Lattice Studies of Gerrymandering Strategies

Kyle Gatesman and James Unwin

Political Analysis, Nov 2020

Abs arXiv

We propose three novel gerrymandering algorithms which incorporate the spatial distribution of voters with the aim of constructing gerrymandered, equal-population, connected districts. Moreover, we develop lattice models of voter distributions, based on analogies to electrostatic potentials, in order to compare different gerrymandering strategies. Due to the probabilistic population fluctuations inherent to our voter models, Monte Carlo methods can be applied to the districts constructed via our gerrymandering algorithms. Through Monte Carlo studies we quantify the effectiveness of each of our gerrymandering algorithms and we also argue that gerrymandering strategies which do not include spatial data lead to (legally prohibited) highly disconnected districts. Of the three algorithms we propose, two are based on different strategies for packing opposition voters, and the third is a new approach to algorithmic gerrymandering based on genetic algorithms, which automatically guarantees that all districts are connected. Furthermore, we use our lattice voter model to examine the effectiveness of isoperimetric quotient tests and our results provide further quantitative support for implementing compactness tests in real-world political redistricting.

2019

2019

hep-ph

Ultraviolet freeze-in and non-standard cosmologies

Nicolás Bernal, Fatemeh Elahi, Carlos Maldonado and James Unwin

Journal of Cosmology and Astroparticle Physics, Nov 2019

Abs arXiv

A notable feature of UV freeze-in is that the relic density is strongly dependent on the highest temperatures of the thermal bath, and a common assumption is that the relevant ’highest temperature’ should be the reheating temperature after inflation TRH. However, the temperature of the thermal bath can be significantly higher in certain scenarios, reaching a value denoted T max , a fact which is only apparent away from the instantaneous decay approximation. Interestingly, it has been shown that if the operators are of sufficiently high mass dimension then the dark matter abundance can be enhanced by a ’boost factor’ depending on (Tmax/TRH) relative to naive estimates assuming instantaneous reheating. We highlight here that in non-standard cosmological histories the critical mass dimension of the operator above at which the instantaneous decay approximation breaks down, and the exponent of the boost factor, depend on the equation of state ω prior to reheating. We highlight four examples in which the dark matter abundance receives a significant enhancement in the context of gravitino dark matter, the moduli portal, the Higgs portal, and the spin-2 portal (as might arise in bimetric gravity models). We comment on the transition from kination domination to radiation domination as a motivated example of non-standard cosmologies.
2019

hep-ph

Establishing the dark matter relic density in an era of particle decays

Carlos Maldonado and James Unwin

Journal of Cosmology and Astroparticle Physics, Jun 2019

Abs arXiv

If the early universe is dominated by an energy density which evolves other than radiation-like the normal Hubble-temperature relation H∝T^2 is broken and dark matter relic density calculations in this era can be significantly different. We first highlight that for a population of states ϕ sourcing an initial expansion rate of the form H∝T^2+n/2 for n≥−4, during the period of appreciable ϕ decays the evolution transitions to H∝T^4. The decays of ϕ imply a source of entropy production in the thermal bath which alters the Boltzmann equations and impacts the dark matter relic abundance. We show that the form of the initial expansion rate leaves a lasting imprint on relic densities established while H∝T^4 since the value of the exponent n changes the temperature evolution of the thermal bath. In particular, a dark matter relic density set via freeze-in or non-thermal production is highly sensitive to the temperature dependance of the initial expansion rate. This work generalises earlier studies which assumed initial expansion rates due to matter or kination domination.
2019

physics.soc-ph

Markov Chain Models of Refugee Migration Data

Vincent Huang and James Unwin

IMA Journal of Applied Mathematics, Jun 2019

Abs arXiv

The application of Markov chains to modelling refugee crises is explored, focusing on local migration of individuals at the level of cities and days. As an explicit example we apply the Markov chains migration model developed here to UNHCR data on the Burundi refugee crisis. We compare our method to a state-of-the-art ‘agent-based’ model of Burundi refugee movements, and highlight that Markov chain approaches presented here can improve the match to data while simultaneously being more algorithmically efficient.
2019

physics.ed-ph

Sonia Kovalevsky Days: The potential to inspire

Laura Schaposnik and James Unwin

AWM Newsletter, Jun 2019

Abs arXiv

The Association of Women in Mathematics has organized and sponsored Sonia Kovalevsky Days for Girls for almost three decades. These one day events are held at colleges and universities in the USA and consist of a program of workshops, talks, and problem solving sessions for female students aged 7-17. In this brief note we would like to give some advice on how to run these events successfully.

2018

2018

hep-ph

Protecting the axion with local baryon number

Michael Duerr, Kai Schmidt-Hoberg and James Unwin

Physics Letters B, May 2018

Abs arXiv

The Peccei-Quinn (PQ) solution to the Strong CP Problem is expected to fail unless the global symmetry U(1)PQ is protected from Planck-scale operators up to high mass dimension. Suitable protection can be achieved if the PQ symmetry is an automatic consequence of some gauge symmetry. We highlight that if baryon number is promoted to a gauge symmetry, the exotic fermions needed for anomaly cancellation can elegantly provide an implementation of the Kim-Shifman-Vainshtein-Zakharov ’hidden axion’ mechanism with a PQ symmetry protected from Planck-scale physics.
2018

hep-ph

Dark matter freeze-out during matter domination

Saleh Hamdan and James Unwin

Modern Physics Letters A, Sep 2018

Abs arXiv

We highlight the general scenario of dark matter freeze-out whilst the energy density of the universe is dominated by a decoupled non-relativistic species. Decoupling during matter domination changes the freeze-out dynamics, since the Hubble rate is parametrically different for matter and radiation domination. Furthermore, for successful Big Bang Nucleosynthesis the state dominating the early universe energy density must decay, this dilutes (or repopulates) the dark matter. As a result, the masses and couplings required to reproduce the observed dark matter relic density can differ significantly from radiation dominated freeze-out.
2018

physics.ed-ph

The phone walkers: a study of human dependence on inactive mobile devices

Laura Schaposnik and James Unwin

Behaviour, Sep 2018

Abs arXiv

The development of mobile phones has largely increased human interactions. Whilst the use of these devices for communication has received significant attention, there has been little analysis of more passive interactions. Through census data on casual social groups, this work suggests a clear pattern of mobile phones being carried in people’s hands, without the person using it (that is, not looking at it). Moreover, this study suggests that when individuals join members of the opposite sex there is a clear tendency to stop holding mobile phones whilst walking. Although it is not clear why people hold their phones whilst walking in such large proportions (38% of solitary women, and 31% of solitary men), we highlight several possible explanation for holding the device, including the need to advertise status and affluence, to maintain immediate connection with friends and family, and to mitigate feelings related to anxiety and security.

2017

2017

hep-ph

Symmetric and asymmetric reheating

Edward Hardy and James Unwin

Journal of High Energy Physics, Sep 2017

Abs arXiv

We study models in which the inflaton is coupled to two otherwise decoupled sectors, and the effect of preheating and related processes on their energy densities during the evolution of the universe. Over most of parameter space, preheating is not disrupted by the presence of extra sectors, and even comparatively weakly coupled sectors can get an order 1 fraction of the total energy at this time. If two sectors are both preheated, the high number densities could also lead to inflaton mediated thermalisation. If only one sector is preheated, Bose enhancement of the late time inflaton decays may cause significant deviations from the perturbative prediction for their relative reheat temperatures. Meanwhile, in Non-Oscillatory inflation models resonant effects can result in exponentially large final temperature differences between sectors that have similar couplings to the inflaton. Asymmetric reheating is potentially relevant for a range of beyond the Standard Model physics scenarios. We show that in dark matter freeze-in models, hidden sector temperatures a factor of 10 below that of the visible sector are typically needed for the relic abundance to be set solely by freeze-in dynamics.
2017

hep-ph

Superheavy thermal dark matter and primordial asymmetries

Joseph Bramante and James Unwin

Journal of High Energy Physics, Feb 2017

Abs arXiv

The early universe could feature multiple reheating events, leading to jumps in the visible sector entropy density that dilute both particle asymmetries and the number density of frozen-out states. In fact, late time entropy jumps are usually required in models of Affleck-Dine baryogenesis, which typically produces an initial particle-antiparticle asymmetry that is much too large. An important consequence of late time dilution, is that a smaller dark matter annihilation cross section is needed to obtain the observed dark matter relic density. For cosmologies with high scale baryogenesis, followed by radiation-dominated dark matter freeze-out, we show that the perturbative unitarity mass bound on thermal relic dark matter is relaxed to 10^10 GeV. We proceed to study superheavy asymmetric dark matter models, made possible by a sizable entropy injection after dark matter freeze-out, and identify how the Affleck-Dine mechanism would generate the baryon and dark asymmetries.
2017

hep-ph

Cores in Dwarf Galaxies from Fermi Repulsion

Lisa Randall, Jakub Scholtz and James Unwin

Monthly Notices of the Royal Astronomical Society, Jan 2017

Abs arXiv

We show that Fermi repulsion can lead to cored density profiles in dwarf galaxies for sub-keV fermionic dark matter. We treat the dark matter as a quasi-degenerate self-gravitating Fermi gas and calculate its density profile assuming hydrostatic equilibrium. We find that suitable dwarf galaxy cores of larger than 130 pc can be achieved for fermion dark matter with mass in the range 70 eV - 400 eV. While in conventional dark matter scenarios, such sub-keV thermal dark matter would be excluded by free streaming bounds, the constraints are ameliorated in models with dark matter at lower temperature than conventional thermal scenarios, such as the Flooded Dark Matter model that we have previously considered. Modifying the arguments of Tremaine and Gunn we derive a conservative lower bound on the mass of fermionic dark matter of 70 eV and a stronger lower bound from Lyman-α clouds of about 470 eV, leading to slightly smaller cores than have been observed. We comment on this result and how the tension is relaxed in dark matter scenarios with non-thermal momentum distributions.
2017

hep-ph

Axial vector Z′ and anomaly cancellation

Ahmed Ismail, Wai-Yee Keung, Kuo-Hsing Tsao and James Unwin

Nuclear Physics B, May 2017

Abs arXiv

Whilst the prospect of new Z′ gauge bosons with only axial couplings to the Standard Model (SM) fermions is widely discussed, examples of anomaly-free renormalisable models are lacking in the literature. We look to remedy this by constructing several motivated examples. Specifically, we consider axial vectors which couple universally to all SM fermions, as well as those which are generation-specific, leptophilic, and leptophobic. Anomaly cancellation typically requires the presence of new coloured and charged chiral fermions, and we argue that in a large class of models masses of these new states are expected to be comparable to that of the axial vector. Finally, an axial vector mediator could provide a portal between SM and hidden sector states, and we also consider the possibility that the axial vector couples to dark matter. If the dark matter relic density is set due to freeze-out via the axial vector, this strongly constrains the parameter space.

2016

2016

hep-ph

Flooded Dark Matter and S level rise

Lisa Randall, Jakub Scholtz and James Unwin

Journal of High Energy Physics, Mar 2016

Abs arXiv

Most dark matter (DM) models set the DM relic density by some interaction with Standard Model particles. Such models generally assume the existence of Standard Model particles early on, with the DM relic density a later consequence of those interactions. Perhaps a more compelling assumption is that DM is not part of the Standard Model sector and a population of DM too is generated at the end of inflation. This democratic assumption does not necessarily provide a natural value for the DM relic density, and superficially leads to too much entropy in the dark sector. We address the latter issue by the late decay of heavy particles produced at early times, associating the DM relic density with the lifetime of a long-lived state. We ask what it would take for this scenario to be compatible with observations in what we call Flooded Dark Matter (FDM) and discuss several interesting consequences. One is that DM can be very light and furthermore, light DM is in some sense the most natural scenario in FDM as it is compatible with larger couplings of the decaying particle. Moreover, the decay of the field with the smallest coupling and hence the longest lifetime dominates the entropy and possibly the matter content of the Universe, a principle we refer to as ’Maximum Baroqueness’. We also show that the dark sector should be colder than the ordinary sector, relaxing the free-streaming constraints on light DM. We will discuss the implications for the core-cusp problem in a follow-up paper. FDM also has interesting baryogenesis implications. One possibility is that both DM and baryon asymmetries are simultaneously diluted by a late entropy dump. Alternatively, FDM is compatible with an elegant non-thermal leptogenesis implementation in which decays of a heavy RH neutrino lead to late time reheating of the Standard Model and provide suitable conditions for creation of a lepton asymmetry.

2015

2015

hep-ph

UltraViolet freeze-in

Fatemeh Elahi, Christopher Kolda and James Unwin

Journal of High Energy Physics, Mar 2015

Abs arXiv

If dark matter is thermally decoupled from the visible sector, the observed relic density can potentially be obtained via freeze-in production of dark matter. Typically in such models it is assumed that the dark matter is connected to the thermal bath through feeble renormalisable interactions. Here, rather, we consider the case in which the hidden and visible sectors are coupled only via non-renormalisable operators. This is arguably a more generic realisation of the dark matter freeze-in scenario, as it does not require the introduction of diminutive renormalisable couplings. We examine general aspects of freeze-in via non-renormalisable operators in a number of toy models and present several motivated implementations in the context of Beyond the Standard Model physics. Specifically, we study models related to the Peccei-Quinn mechanism and Z’ portals.

2014

2014

hep-ph

Fitting the Galactic Center γ-ray excess with cascade annihilations

Adam Martin, Jessie Shelton and James Unwin

Physical Review D, Nov 2014

Abs arXiv

The apparent excess of gamma rays in an extended region in the direction of the galactic center has a spatial distribution and amplitude that are suggestive of dark matter annihilations. If this excess is indeed due to dark matter annihilations, it would indicate the presence of both dark matter and an additional particle beyond the Standard Model that mediates the interactions between the dark matter and Standard Model states. We introduce reference models describing dark matter annihilation to pairs of these new mediators, which decouples the SM-mediator coupling from the thermal annihilation cross section and easily explains the lack of direct detection signals. We determine the parameter regions that give good descriptions of the gamma ray excess for several motivated choices of mediator couplings to the SM. We find fermion dark matter with mass 7-26 GeV and a dark vector mediator, or scalar dark matter in the 10-50 GeV range (Higgs portal mediator) or 10-65 GeV range (gluophilic mediator) can provide a comparable or improved fit, compared to the case of direct annihilation. We demonstrate that these models can easily satisfy all constraints from collider experiments, direct detection, and cosmology.
2014

hep-ph

Towards cogenesis via Asymmetric Freeze-In: the χwho came-in from the cold

James Unwin

Journal of High Energy Physics, Oct 2014

Abs arXiv

In models of freeze-in the dark matter (DM) is decoupled from the visible sector and initially has a depleted number density. The hidden and visible sectors are connected only via a feeble portal interaction by which DM can be produced. Asymmetric freeze-in (AFI) combines this scenario with ideas from asymmetric DM and provides a potential cogenesis mechanism. However, it has been argued that existing AFI models do not produce suitably large particle asymmetries due to cancellations which arises because the mediator state remains in thermal equilibrium. We examine AFI via an out-of-equilibrium mediator and using a simple scalar model show that in this case sizeable asymmetries may be generated.
2014

hep-th

Precision unification and proton decay in F-theory GUTs with high scale supersymmetry

Arthur Hebecker and James Unwin

Journal of High Energy Physics, Sep 2014

Abs arXiv

F-theory GUTs provide a promising UV completion for models with approximate gauge coupling unification, such as the (non-supersymmetric) Standard Model. More specifically, if the superparters have masses well above the TeV scale, the resulting imperfection in unification can be accounted for by the, in principle calculable, classical F-theory correction at the high scale. In this paper we argue for the correct form of the F-theory corrections to unification, including KK mode loop effects. However, the price of compensating the imprecise unification in such High Scale SUSY models with F-theory corrections is that the GUT scale is lowered, potentially leading to a dangerously high proton decay rate from dimension-6 operators. We analyse the possibility of suppressing the decay rate by the localization of X,Y gauge bosons in higher dimensions. While this effect can be very strong for the zero modes, we find that in the simplest models of this type it is difficult to realize a significant suppression for higher modes (Landau levels). Notably, in the absence of substantial suppressions to the proton decay rate, the superpartners must be lighter than 100 TeV to satisfy proton decay constraints. We highlight that multiple correlated signals of proton decay could verify this scenario.
2014

hep-ph

X-ray lines from R-parity violating decays of keV sparticles

Christopher Kolda and James Unwin

Physical Review D, Jul 2014

Abs arXiv

Download PDF If R-parity is only mildly violated then the lightest supersymmetric particle (LSP) can be stable over cosmologically time-scales and still account for the dark matter relic density. We examine the possibility of generating detectable X-ray lines from R-parity violating decays of keV-scale LSP dark matter to neutrino-photon pairs. Specifically, we consider scenarios in which the LSP is a light gravitino, bino, or hidden sector photino. Potential signals are discussed in the context of recent claims of an unidentified 3.5 keV X-ray line in studies of stacked galaxy clusters. We comment on the difficulties in obtaining the observed relic density for keV scale bino or hidden photino dark matter and some possible resolutions.
2014

hep-ph

Annihilation signals from asymmetric dark matter

Edward Hardy, Robert Lasenby and James Unwin

Journal of High Energy Physics, Jul 2014

Abs arXiv

In the simplest models of asymmetric dark matter (ADM) annihilation signals are not expected, since the DM is non-self-conjugate and the relic density of anti-DM is negligible. We investigate a new class of models in which a symmetric DM component, in the ‘low-mass’ 1-10 GeV regime favoured for linking the DM and baryon asymmetries, is repopulated through decays. We find that, in models without significant velocity dependence of the annihilation cross section, observational constraints generally force these decays to be (cosmologically) slow. These late decays can give rise to gamma-ray signal morphologies differing from usual annihilation profiles. A distinctive feature of such models is that signals may be absent from dwarf spheroidal galaxies.

2013

2013

thesis

On connections between dark matter and the baryon asymmetry

James A. Unwin

Journal of High Energy Physics, Jul 2013

Abs

This thesis is dedicated to the study of a prominent class of dark matter (DM) models, in which the DM relic density is linked to the baryon asymmetry, often referred to as Asymmetric Dark Matter (ADM) theories. In ADM the relic density is set by a particle-antiparticle asymmetry, in direct analogue to the baryons. This is partly motivated by the observed proximity of the baryon and DM relic densities Ω_DM ≈ 5 Ω_B, as this can be explained if the DM and baryon asymmetries are linked. A general requisite of models of ADM is that the vast majority of the symmetric component of the DM number density, the DM-antiDM pairs, must be removed for the asymmetry to set the DM relic density and thus to explain the coincidence of Ω_DM and Ω_B. However we shall argue that demanding the efficient annihilation of the symmetric component leads to a tension with experimental constraints in a large class of models. In order to satisfy the limits coming from direct detection and colliders searches, it is almost certainly required that the DM be part of a richer hidden sector of interacting states. Subsequently, examples of such extended hidden sectors are constructed and studied, in particular we highlight that the presence of light pseudoscalars can greatly aid in alleviating the experimental bounds and are well motivated from a theoretical stance. Finally, we highlight that self-conjugate DM can be generated from hidden sector particle asymmetries, which can lead to distinct phenomenology. Further, this variant on the ADM scenario can circumvent some of the leading constraints.
2013

hep-ph

The impact of heavy-quark loops on LHC dark-matter searches

Ulrich Haisch, Felix Kahlhoefer and James Unwin

Journal of High Energy Physics, Jul 2013

Abs arXiv

If only tree-level processes are included in the analysis, LHC monojet searches give weak constraints on the dark matter-proton scattering cross section arising from the exchange of a new heavy scalar or pseudoscalar mediator with Yukawa-like couplings to quarks. In this letter we calculate the constraints on these interactions from the CMS 5.0/fb and ATLAS 4.7/fb searches for jets with missing energy including the effects of heavy-quark loops. We find that the inclusion of such contributions leads to a dramatic increase in the predicted cross section and therefore a significant improvement of the bounds from LHC searches.
2013

hep-ph

Exodus: Hidden origin of dark matter and baryons

James Unwin

Journal of High Energy Physics, Jun 2013

Abs arXiv

We propose a new framework for explaining the proximity of the baryon and dark matter relic densities \Omega_DM ≈5\Omega_B. The scenario assumes that the number density of the observed dark matter states is generated due to decays from a second hidden sector which simultaneously generates the baryon asymmetry. In contrast to asymmetric dark matter models, the dark matter can be a real scalar or Majorana fermion and thus presents distinct phenomenology. We discuss aspects of model building and general constraints in this framework. We present a simple supersymmetric implementation of this mechanism and show that it can be used to obtain the correct dark matter relic density for a bino LSP.

2012

2012

hep-ph

R-symmetric high scale supersymmetry

James Unwin

Physical Review D, Nov 2012

Abs arXiv

Introducing an R-symmetry to models of high scale supersymmetry (SUSY) can have interesting consequences, and we focus on two aspects. If Majorana masses are forbidden by an R-symmetry and the main source of electroweak gaugino masses are Dirac terms, then the Higgs quartic coupling vanishing at the SUSY scale and the Higgs boson mass will be near 125 GeV. Moreover, using an R-symmetry, models with only one Higgs doublet in the UV can be constructed and we argue that, since we desire only a single Higgs at the weak scale, this scenario is more aesthetic than existing models. We subsequently present a model which draws on both of these features. We comment on neutrino masses and dark matter in these scenarios and discuss how the models presented can be discerned from alternative constructions with high scale SUSY, including Split SUSY.
2012

hep-ph

Precision unification in \lambdaSUSY with a 125GeV Higgs

Edward Hardy, John March-Russell and James Unwin

Journal of High Energy Physics, Oct 2012

Abs arXiv

It is challenging to explain the tentative 125 GeV Higgs signal in the Minimal Supersymmetric Standard Model (MSSM) without introducing excessive fine-tuning, and this motivates the study of non-minimal implementations of low energy supersymmetry (SUSY). A term λSH_uH_d involving a Standard Model (SM) singlet state S leads to an additional source for the quartic interaction raising the mass of the lightest SM-like Higgs. However, in order to achieve m_h ≈125 GeV with light stops and small stop mixing, it is necessary for λ≳0.7 and consequently λmay become non-perturbative before the unification scale. Moreover, as argued by Barbieri, Hall, et al. low fine-tuning prefers the region λ 1-2, leading to new or non-perturbative physics involving S below the GUT scale (‘λSUSY’ models). This raises the concern that precision gauge coupling unification, the prime piece of indirect experimental evidence for low energy SUSY, may be upset. Using the NSVZ exact β-function along with well motivated assumptions on the strong coupling dynamics we show that this is not necessarily the case, but rather there exist classes of UV completions where the strong-coupling effects can naturally correct for the present 3% discrepancy in the two-loop MSSM unification prediction for \alpha_s. Moreover, we argue that in certain scenarios a period of strong coupling can also be beneficial for t-b unification, while maintaining the small to moderate values of tanβpreferred by the Higgs mass.
2012

hep-ph

Closing in on asymmetric dark matter I: model independent limits for interactions with quarks

John March-Russell, James Unwin and Stephen M. West

Journal of High Energy Physics, Aug 2012

Abs arXiv

It is argued that experimental constraints on theories of asymmetric dark matter (ADM) almost certainly require that the DM be part of a richer hidden sector of interacting states of comparable mass or lighter. A general requisite of models of ADM is that the vast majority of the symmetric component of the DM number density must be removed in order to explain the observed relationship ΩB∼ΩDM via the DM asymmetry. Demanding the efficient annihilation of the symmetric component leads to a tension with experimental limits if the annihilation is directly to Standard Model (SM) degrees of freedom. A comprehensive effective operator analysis of the model independent constraints on ADM from direct detection experiments and LHC monojet searches is presented. Notably, the limits obtained essentially exclude models of ADM with mass 1GeV≲mDM≲ 100GeV annihilating to SM quarks via heavy mediator states. This motivates the study of portal interactions between the dark and SM sectors mediated by light states. Resonances and threshold effects involving the new light states are shown to be important for determining the exclusion limits.

2011

2011

hep-ph

A sharp 141 GeV Higgs prediction from environmental selection

James Unwin

arXiv preprint, Nov 2011

Abs arXiv

We construct an environmentally selected supersymmetric standard model with a single Higgs doublet, in analogy with the work of Hall and Nomura. The low energy spectrum presents only the standard model states with a single Higgs and TeV scale gauginos. The model features a precise Higgs mass prediction m_H=141\pm 2 GeV and the neutral wino provides a viable dark matter candidate.
2011

hep-ph

Vacuum stability and the Cholesky decomposition

James Unwin

The European Physical Journal C, May 2011

Abs arXiv

We discuss how the Cholesky decomposition may be used to ascertain whether a critical point of the field theory scalar potential provides a stable vacuum configuration. We then use this method to derive the stability conditions in a specific example.