26 research outputs found

### The Abundance of Kaluza-Klein Dark Matter with Coannihilation

In Universal Extra Dimension models, the lightest Kaluza-Klein (KK) particle
is generically the first KK excitation of the photon and can be stable, serving
as particle dark matter. We calculate the thermal relic abundance of the KK
photon for a general mass spectrum of KK excitations including full
coannihilation effects with all (level one) KK excitations. We find that
including coannihilation can significantly change the relic abundance when the
coannihilating particles are within about 20% of the mass of the KK photon.
Matching the relic abundance with cosmological data, we find the mass range of
the KK photon is much wider than previously found, up to about 2 TeV if the
masses of the strongly interacting level one KK particles are within five
percent of the mass of the KK photon. We also find cases where several
coannihilation channels compete (constructively and destructively) with one
another. The lower bound on the KK photon mass, about 540 GeV when just
right-handed KK leptons coannihilate with the KK photon, relaxes upward by
several hundred GeV when coannihilation with electroweak KK gauge bosons of the
same mass is included.Comment: 38 pages, 4 figure

### Anomalous Symmetry Fractionalization and Surface Topological Order

In addition to possessing fractional statistics, anyon excitations of a 2D
topologically ordered state can realize symmetry in distinct ways , leading to
a variety of symmetry enriched topological (SET) phases. While the symmetry
fractionalization must be consistent with the fusion and braiding rules of the
anyons, not all ostensibly consistent symmetry fractionalizations can be
realized in 2D systems. Instead, certain `anomalous' SETs can only occur on the
surface of a 3D symmetry protected topological (SPT) phase. In this paper we
describe a procedure for determining whether an SET of a discrete, onsite,
unitary symmetry group $G$ is anomalous or not. The basic idea is to gauge the
symmetry and expose the anomaly as an obstruction to a consistent topological
theory combining both the original anyons and the gauge fluxes. Utilizing a
result of Etingof, Nikshych, and Ostrik, we point out that a class of
obstructions are captured by the fourth cohomology group $H^4( G, \,U(1))$,
which also precisely labels the set of 3D SPT phases, with symmetry group $G$.
We thus establish a general bulk-boundary correspondence between the anomalous
SET and the 3d bulk SPT whose surface termination realizes it. We illustrate
this idea using the chiral spin liquid ($U(1)_2$) topological order with a
reduced symmetry $\mathbb{Z}_2 \times \mathbb{Z}_2 \subset SO(3)$, which can
act on the semion quasiparticle in an anomalous way. We construct exactly
solved 3d SPT models realizing the anomalous surface terminations, and
demonstrate that they are non-trivial by computing three loop braiding
statistics. Possible extensions to anti-unitary symmetries are also discussed.Comment: 18 pages + 3 pages appendices. v2: added section on identifying the
SPT order from nontrivial loop statistics in the 3D bulk with projective
semion surface stat

### Time reversal invariant gapped boundaries of the double semion state

The boundary of a fractionalized topological phase can be gapped by
condensing a proper set of bosonic quasiparticles. Interestingly, in the
presence of a global symmetry, such a boundary can have different symmetry
transformation properties. Here we present an explicit example of this kind, in
the double semion state with time reversal symmetry. We find two distinct cases
where the semionic excitations on the boundary can transform either as time
reversal singlets or as time reversal (Kramers) doublets, depending on the
coherent phase factor of the Bose condensate. The existence of these two
possibilities are demonstrated using both field theory argument and exactly
solvable lattice models. Furthermore, we study the domain walls between these
two types of gapped boundaries and find that the application of time reversal
symmetry tunnels a semion between them.Comment: 11 pages, 8 figure

### From tunnels to towers: quantum scars from Lie Algebras and q-deformed Lie Algebras

We present a general symmetry-based framework for obtaining many-body
Hamiltonians with scarred eigenstates that do not obey the eigenstate
thermalization hypothesis. Our models are derived from parent Hamiltonians with
a non-Abelian (or q-deformed) symmetry, whose eigenspectra are organized as
degenerate multiplets that transform as irreducible representations of the
symmetry (`tunnels'). We show that large classes of perturbations break the
symmetry, but in a manner that preserves a particular low-entanglement
multiplet of states -- thereby giving generic, thermal spectra with a `shadow'
of the broken symmetry in the form of scars. The generators of the Lie algebra
furnish operators with `spectrum generating algebras' that can be used to lift
the degeneracy of the scar states and promote them to equally spaced `towers'.
Our framework applies to several known models with scars, but we also introduce
new models with scars that transform as irreducible representations of
symmetries such as SU(3) and $q$-deformed SU(2), significantly generalizing the
types of systems known to harbor this phenomenon. Additionally, we present new
examples of generalized AKLT models with scar states that do not transform in
an irreducible representation of the relevant symmetry. These are derived from
parent Hamiltonians with enhanced symmetries, and bring AKLT-like models into
our framework.Comment: v2- published versio

### Anomalous crystalline-electromagnetic responses in semimetals

We present a unifying framework that allows us to study the mixed
crystalline-electromagnetic responses of topological semimetals in spatial
dimensions up to $D = 3$ through dimensional augmentation and reduction
procedures. We show how this framework illuminates relations between the
previously known topological semimetals, and use it to identify a new class of
quadrupolar nodal line semimetals for which we construct a lattice
tight-binding Hamiltonian. We further utilize this framework to quantify a
variety of mixed crystalline-electromagnetic responses, including several that
have not previously been explored in existing literature, and show that the
corresponding coefficients are universally proportional to weighted
momentum-energy multipole moments of the nodal points (or lines) of the
semimetal. We introduce lattice gauge fields that couple to the crystal
momentum and describe how tools including the gradient expansion procedure,
dimensional reduction, compactification, and the Kubo formula can be used to
systematically derive these responses and their coefficients. We further
substantiate these findings through analytical physical arguments, microscopic
calculations, and explicit numerical simulations employing tight-binding
models

### Ovarian cancer screening and mortality in the UK Collaborative Trial of Ovarian Cancer Screening (UKCTOCS): a randomised controlled trial

Background Ovarian cancer has a poor prognosis, with just 40% of patients surviving 5 years. We designed this trial
to establish the eff ect of early detection by screening on ovarian cancer mortality.
Methods In this randomised controlled trial, we recruited postmenopausal women aged 50â€“74 years from 13 centres in
National Health Service Trusts in England, Wales, and Northern Ireland. Exclusion criteria were previous bilateral oophorectomy or ovarian malignancy, increased risk of familial ovarian cancer, and active non-ovarian malignancy. The trial management system confirmed eligibility and randomly allocated participants in blocks of 32 using computergenerated random numbers to annual multimodal screening (MMS) with serum CA125 interpreted with use of the risk of ovarian cancer algorithm, annual transvaginal ultrasound screening (USS), or no screening, in a 1:1:2 ratio. The primary outcome was death due to ovarian cancer by Dec 31, 2014, comparing MMS and USS separately with no screening, ascertained by an outcomes committee masked to randomisation group. All analyses were by modified intention to screen, excluding the small number of women we discovered after randomisation to have a bilateral oophorectomy, have ovarian cancer, or had exited the registry before recruitment. Investigators and participants were aware of screening type. This trial is registered with ClinicalTrials.gov, number NCT00058032.
Findings Between June 1, 2001, and Oct 21, 2005, we randomly allocated 202 638 women: 50 640 (25Â·0%) to MMS,
50 639 (25Â·0%) to USS, and 101 359 (50Â·0%) to no screening. 202 546 (>99Â·9%) women were eligible for analysis: 50 624 (>99Â·9%) women in the MMS group, 50 623 (>99Â·9%) in the USS group, and 101 299 (>99Â·9%) in the no
screening group. Screening ended on Dec 31, 2011, and included 345 570 MMS and 327 775 USS annual screening
episodes. At a median follow-up of 11Â·1 years (IQR 10Â·0â€“12Â·0), we diagnosed ovarian cancer in 1282 (0Â·6%) women:
338 (0Â·7%) in the MMS group, 314 (0Â·6%) in the USS group, and 630 (0Â·6%) in the no screening group. Of these women, 148 (0Â·29%) women in the MMS group, 154 (0Â·30%) in the USS group, and 347 (0Â·34%) in the no screening group had died of ovarian cancer. The primary analysis using a Cox proportional hazards model gave a mortality reduction over years 0â€“14 of 15% (95% CI â€“3 to 30; p=0Â·10) with MMS and 11% (â€“7 to 27; p=0Â·21) with USS. The Royston-Parmar fl exible parametric model showed that in the MMS group, this mortality eff ect was made up of 8% (â€“20 to 31) in years 0â€“7 and 23% (1â€“46) in years 7â€“14, and in the USS group, of 2% (â€“27 to 26) in years 0â€“7 and 21% (â€“2 to 42) in years 7â€“14. A prespecified analysis of death from ovarian cancer of MMS versus no screening with exclusion of prevalent cases showed significantly diff erent death rates (p=0Â·021), with an overall average mortality reduction of 20% (â€“2 to 40) and a reduction of 8% (â€“27 to 43) in years 0â€“7 and 28% (â€“3 to 49) in years 7â€“14 in favour of MMS.
Interpretation Although the mortality reduction was not signifi cant in the primary analysis, we noted a signifi cant mortality reduction with MMS when prevalent cases were excluded. We noted encouraging evidence of a mortality reduction in years 7â€“14, but further follow-up is needed before firm conclusions can be reached on the efficacy and cost-eff ectiveness of ovarian cancer screening