F42 | Macro Paper Warehouse

Destabilizing Capital Flows amid Global Inflation

Mon, 01 Jan 0001 00:00:00 +0000

Layer 1 — Overview

Research Question

Bengui and Coulibaly ask whether the pattern of capital flows observed during the 2021–2023 global monetary tightening cycle — whereby capital flowed from low-inflation to high-inflation countries — was a stabilizing or destabilizing force for the global economy’s adjustment to cost-push shocks. Among the G7 and a broader sample of 26 jurisdictions, those with higher average CPI inflation (October 2021–March 2023) and larger cumulative interest rate hikes ran more negative current account balances over the same period, with the slope of the cross-sectional relationship between cumulative hikes and the current account equal to −1.29 (significant at 1%) and the slope between average inflation and the current account equal to −0.99 (significant at 1%), and over 75% of the top two quartile hikers running deficits while over 75% of the bottom two quartiles ran surpluses.

Model and Methodology

The authors build a standard continuous-time two-country general equilibrium model with nominal rigidities (Calvo price-setting), internationally traded bonds, and cost-push shocks modeled as wage markup shocks that create an output-inflation trade-off. The baseline model features no home bias (equal weights on domestic and foreign goods) and two tradable goods. Extensions introduce (i) consumption home bias (parameter α ∈ [0, 1/2]) and (ii) non-tradable goods. Policy is analyzed under two regimes: (a) free capital mobility (no taxes on financial transactions) with optimal cooperative monetary policy, and (b) a managed capital flow regime in which a planner jointly optimizes both monetary policy and a tax wedge on the international bond (τ^D_t). A second-order approximation of household utility yields a loss function penalizing world and cross-country output gaps, PPI inflation differentials, and the demand imbalance term θ_t. The quantitative section replaces optimal monetary policy with standard Taylor rules (φ_π = 1.5, φ_y = 0.25) and calibrates a Home cost-push shock to generate a peak CPI inflation rate of about 7%, with an annual autocorrelation of 0.65.

Main Findings

The paper’s central theoretical result (Proposition 2, “Topsy-Turvy Capital Flows”) is that, under the Marshall-Lerner condition (trade elasticity η > 1), a free capital mobility regime channels capital into the country with the most acute inflationary pressures — the very country whose central bank is most aggressively tightening — while the constrained-efficient managed regime would channel capital in the opposite direction. The mechanism operates through the supply side: capital inflows raise domestic households’ wealth, reducing their labor supply and thereby raising real wages and firms’ marginal costs. In the presence of non-tradable goods, an additional channel operates through the real exchange rate — capital inflows appreciate the domestic real exchange rate and inflate tradable-sector firms’ marginal costs independently of labor supply. Both channels worsen the central bank’s output-inflation trade-off.

In the quantitative exercise (Taylor rule setting, home bias α = 0.25, trade elasticity χ = 3), following the calibrated inflationary cost-push shock in Home:

Under free capital mobility: Home inflation rises to 8% on impact; Home output gap reaches −8.4%; Foreign output gap reaches +2.4%; Home runs a trade deficit of 2.5% of GDP on impact; Home’s initial policy rate hike is nearly 10% while Foreign’s is less than 1%.
Under the managed capital flow regime (capital flows reversed to outflows from Home): Home inflation on impact falls to nearly 6% (a reduction of approximately 2 percentage points); Home output gap is −6.8% (improvement of about 1.5 percentage points); Foreign output gap is 0.8% (improvement of about 1.5 percentage points); Home runs a trade surplus of 0.6% of GDP; Home’s initial hike falls to approximately 8% (roughly 2 percentage points lower) while Foreign’s rises to approximately 2.5% (roughly 1.5 percentage points higher).
The managed regime delivers average welfare gains of 0.78% of current consumption (0.03% of permanent consumption). Welfare gains are increasing in the trade elasticity η: at η = 10 (consistent with Yi 2003’s bilateral trade flow estimates), gains reach approximately 0.08% of permanent consumption or 1.9% of current consumption.

Scope Conditions

The topsy-turvy result (free mobility channels capital in the wrong direction) holds conditional on the Marshall-Lerner condition (η > 1 in the baseline; equivalently, the trade elasticity χ > 1). With consumption home bias, the condition weakens to: the trade elasticity exceeds the degree of home bias (χ > 1 − 2α, which is weaker than Marshall-Lerner). When home bias is strong relative to the trade elasticity, a purchasing power effect may dominate the wealth effect, and free capital mobility may instead deliver too little capital flow toward the depressed country — the opposite inefficiency. The welfare analysis throughout assumes symmetric initial net foreign asset positions. The key insight is specific to environments in which monetary policy faces an output-inflation trade-off from cost-push shocks; it is directionally opposite to the aggregate demand externality prescription that arises in demand-shortage environments (e.g., currency unions with productivity shocks), where optimal policy instead calls for capital to flow toward the more depressed country.

Layer 2 — Q&A

Q1: What is the empirical motivation for the paper, and how is the stylized fact documented?

A1: During October 2021–March 2023, jurisdictions with higher average CPI inflation and larger cumulative policy rate hikes ran more negative current account balances. The cross-sectional slope between average inflation and the current account-to-GDP ratio is −0.99 (R² = 0.22, significant at 1%), while the slope between cumulative hikes and the current account is −1.29 (R² = 0.27, significant at 1%). Among the top two quartiles of cumulative hikers, over 75% of jurisdictions ran current account deficits, while among the bottom two quartiles over 75% ran surpluses. Data come from the BIS (inflation and policy rates) and the OECD Main Economic Indicators (quarterly current accounts), covering 26 jurisdictions excluding Argentina, Russia, and Turkey.

Q2: What is the core externality the paper identifies, and why do atomistic agents fail to internalize it?

A2: When a household in the high-inflation country borrows from abroad for consumption smoothing (as the domestic central bank tightens), it raises domestic consumption and thereby reduces labor supply through a wealth effect, pushing up real wages and firms’ marginal costs. The central bank must then tighten further to achieve the same inflation stabilization, or accept a worse inflation outcome. Because this effect operates through economy-wide wages and prices (general equilibrium), atomistic households do not internalize it when making individual borrowing decisions. The paper shows formally that a marginal increase in Home borrowing dθ_t raises welfare losses by an amount proportional to the product of the Phillips curve slope κ, the co-state variable φ^D_t (equal to the cross-country output gap differential y^D_t under optimal monetary policy), and the direct effect on cross-country marginal cost differences (1/2). When output is more depressed in Home (y^D_t < 0), additional borrowing by Home tightens the constraint and lowers welfare.

Q3: What does the optimal capital flow management targeting rule say, and what is its economic interpretation?

A3: Proposition 1 states that under jointly optimal monetary and capital flow management, the demand imbalance (relative consumption) should satisfy θ_t = 2y^D_t. This means the planner generates a demand imbalance in favor of the less depressed country, reallocating spending away from the country with the most acute inflationary pressure. This is counterintuitive from a pure output stabilization view: policy deliberately shifts demand away from the country with the most depressed output. The logic is that reducing the domestic wealth of the high-inflation country lowers real wages, reduces firms’ marginal costs, and thereby relaxes the output-inflation trade-off for that country’s central bank.

Q4: What is the “topsy-turvy” capital flows result (Proposition 2), and under what condition does it hold?

A4: Under free capital mobility, standard neoclassical consumption-smoothing motives lead capital to flow into the country with the most depressed output (the high-inflation country): the trade deficit equals [(η−1)/η]·y^D_t. Under managed capital flows, the optimal regime instead mandates a trade surplus for the most depressed country: the trade balance equals −(1/η)·y^D_t. Comparing signs, the direction of capital flows is literally reversed — hence “topsy-turvy.” The result holds whenever Assumption 1 (η > 1, the Marshall-Lerner condition in the baseline model) is satisfied, which the authors argue has compelling empirical support (trade elasticities estimated at 7–17 in the literature).

Q5: How does the presence of home bias in consumption affect the externality and the topsy-turvy result?

A5: With home bias (α < 1/2), capital inflows also appreciate the terms of trade, which lowers the relative price of imports in terms of domestic goods and reduces marginal costs for domestic tradable firms — a “purchasing power effect” that partially offsets the wealth effect. The optimal capital flow targeting rule becomes θ_t = [1 − (1−2α)/(2(1−α)η)]·2y^D_t. Under the condition that the trade elasticity exceeds the degree of home bias (χ > 1 − 2α, strictly weaker than Marshall-Lerner), the wealth effect dominates the purchasing power effect and the topsy-turvy result is preserved. Below a knife-edge curve in the (α, η) parameter space, the purchasing power effect dominates and free capital mobility results in too little rather than too much capital flowing toward the high-inflation country.

Q6: Does the externality always imply excessive capital flow volatility?

A6: No — this is a novel contribution relative to the prior literature. In the limiting case of a unit intratemporal elasticity (η → 1, the Cole-Obstfeld case), trade is balanced at all times under free capital mobility. Under managed capital flows, however, capital should flow from the most depressed to the least depressed country. This means the externality can result in too little rather than too much capital flow. The standard normative literature (e.g., Bianchi 2011) has focused on excessive capital flow volatility; the supply-side channel identified here shows that market failures can sometimes lead to insufficient external imbalances.

Q7: How does the paper’s mechanism differ from aggregate demand externalities as in Farhi and Werning (2016)?

A7: Farhi and Werning (2016) study demand-shortage environments (fixed exchange rates or zero lower bound) where constraints on monetary policy mean output is demand-constrained. Their prescription is to channel capital toward the most depressed country to stimulate demand for undersupplied goods. In Bengui and Coulibaly, monetary policy is unconstrained but faces an output-inflation trade-off from cost-push shocks. Here, the depressed output reflects the central bank’s deliberate demand contraction to fight inflation, not an inability to stimulate. The optimal response is therefore to shift spending away from the high-inflation (most depressed) country to reduce supply pressure — the opposite direction. Formally, in the demand-shortage case with unit elasticity and home bias, the optimal trade balance targeting rule is nxt = [(1−2α)/(4(1−α))]·ỹ^D_t (trade deficit for most depressed country), while in the supply pressure case it is nxt = −[α/(1−α)]·y^D_t (trade surplus for most depressed country).

Q8: What does the non-tradable goods extension add to the baseline mechanism?

A8: The baseline model (two tradable goods, no home bias) transmits the externality only through the wealth effect on labor supply: capital inflows raise consumption, reduce labor supply, and raise real wages and marginal costs. In the non-tradable goods extension, a second channel operates through the real exchange rate. Capital inflows raise demand for non-tradable goods, appreciating the domestic real exchange rate and inflating the price of the consumption basket relative to domestically produced tradable goods. This raises marginal costs for tradable-sector firms independently of any labor supply response, and is therefore unaffected by whether preferences exhibit a wealth effect on labor supply. The paper shows that the optimal policy problem in this extension is isomorphic to the baseline: the loss decomposition (equation 42) yields two additive terms proportional to the share of tradable goods (wealth effect on labor supply) and the share of non-tradable goods (wealth effect on demand for non-tradables), respectively.

Q9: What does the quantitative exercise show about cross-country policy rate dispersion?

A9: Under free capital mobility with Taylor rules, the initial policy rate hike in Home following the calibrated shock is nearly 10%, while in Foreign it is less than 1% — a cross-country dispersion of roughly 9 percentage points. Under managed capital flows, Home’s initial hike falls to approximately 8% and Foreign’s rises to approximately 2.5% — a dispersion of roughly 5.5 percentage points. The authors interpret this as evidence that free capital mobility leads high-inflation countries to tighten excessively and low-inflation countries to tighten too little, generating an inefficiently large cross-country dispersion in monetary policy.

Q10: How does the welfare gain from managed capital flows vary with the trade elasticity?

A10: Welfare gains are increasing in the elasticity of substitution between domestic and foreign goods (η). At the baseline calibration of η = 2 (trade elasticity χ = 3, near the lower bound of empirical estimates), the gain is 0.78% of current consumption (0.03% of permanent consumption). At η = 10 (consistent with Yi 2003’s estimate needed to match bilateral trade flows), the gain rises to approximately 1.9% of current consumption (0.08% of permanent consumption). The welfare gain is defined as the percentage increase in permanent consumption required by a household under free capital mobility to be as well off as under managed capital flows.

Q11: What is the role of Lemma 1 (irrelevance of capital flow regime for world variables)?

A11: Lemma 1 shows that under optimal cooperative monetary policy, the paths of world output gap and world inflation are independent of the capital flow regime (i.e., independent of the path of θ_t). This follows because the “world” block of the model can be solved independently of the “difference” block and the demand imbalance. As a result, the entire normative analysis of capital flows reduces to the behavior of cross-country difference variables (y^D_t, π^D_t, and θ_t), greatly simplifying the analysis. It also implies that switching capital flow regimes does not affect the global total of output or inflation, only its distribution across countries.

Q12: What extensions do the authors suggest would enrich the analysis without invalidating the main insight?

A12: Three extensions are noted. First, additional monetary policy constraints — discretionary (non-commitment) policy, non-cooperative policy setting, or a currency union — would introduce extra stabilization constraints and generate additional terms in the capital flow management targeting rule but would not overturn the supply-side channel. Second, alternative goods pricing specifications (local currency pricing, deviations from the law of one price) would make additional variables like cross-country consumer price differentials relevant measures of policy tightness, again adding terms to the rule. Third, the insight is argued to apply more generally in heterogeneous-agent or multi-sector closed-economy models with nominal rigidities whenever private financial decisions affect the economy’s supply side through general equilibrium price effects.

Key Concepts

Cost-push shock (wage markup shock): In the paper’s model, a cost-push shock is a positive deviation of the wage markup (µ^w_t) from its steady-state value. It shifts the New Keynesian Phillips curve, creating an output-inflation trade-off: the central bank must accept either higher inflation or a larger negative output gap. It is not a demand shock; its policy implications are directionally opposite to demand shortage shocks.

Demand imbalance (θ_t): The log ratio of Home to Foreign consumption, defined as c_t − c^*_t = θ_t in the linearized model. Under free capital mobility and symmetric initial wealth, θ_t = 0 (consumption shares are equalized). Under managed capital flows, θ_t is the instrument of capital flow policy: setting θ_t > 0 shifts spending toward Home; θ_t < 0 shifts it toward Foreign. The loss function penalizes deviations of θ_t from zero as an independent inefficiency (cross-country consumption misallocation).

Topsy-turvy capital flows: The paper’s central finding that, following a cost-push shock, the direction of capital flows prescribed by constrained-efficient policy is opposite to the direction that free capital mobility generates. Under free mobility, capital flows into the high-inflation country (trade deficit there); under managed flows, capital should flow out of the high-inflation country (trade surplus there). The term is used to describe the directional reversal, not merely excessive magnitude.

Macroeconomic externality (supply-side): The failure of atomistic agents to internalize the general equilibrium effect of their borrowing decisions on domestic firms’ marginal costs (via real wages or the real exchange rate). This is the paper’s label for the source of inefficiency. It is classified as a supply-side externality to distinguish it from aggregate demand externalities (Farhi and Werning 2016), where the operative mechanism runs through demand for specific goods rather than through factor costs.

Trade elasticity (χ): In the baseline model, χ = η (elasticity of substitution between domestic and foreign tradable goods). With home bias, χ = 2(1−α)η. The trade elasticity plays the key role in determining whether the topsy-turvy result holds: the result requires χ > 1 (Marshall-Lerner in baseline) or, with home bias, χ > 1 − 2α (weaker condition). At χ = 1 (Cole-Obstfeld case), trade is balanced under free mobility, and managed flows call for capital to move from the most to the least depressed country — implying insufficient rather than excessive capital flows under free mobility.

Purchasing power effect: In the model with home bias, a capital inflow appreciates the terms of trade (the relative price of exports over imports), which raises the purchasing power of domestic firms and lowers their marginal costs. This effect partially offsets the wealth-effect-driven rise in marginal costs. Its strength is proportional to the degree of home bias (1−2α) relative to the trade elasticity 2(1−α)η. Under the paper’s weaker-than-Marshall-Lerner condition, the wealth effect dominates the purchasing power effect.

Managed capital flow regime: A policy regime in which the government imposes taxes on international financial transactions (τ_t for Home, τ^_t for Foreign) to control the demand imbalance θ_t, subject to the targeting rule θ_t = 2y^D_t (or its home-bias-adjusted counterpart). This regime accounts for the macroeconomic externality and delivers a constrained-efficient allocation given the presence of nominal rigidities. The tax wedge τ^D_t = (τ_t − τ^_t)/2 represents the gap in returns on the international bond faced by Home versus Foreign households.

World and difference formulation: Following Engel (2011) and Groll and Monacelli (2020), the model is decomposed into “world” variables (averages: y^W_t, π^W_t) and “difference” variables (cross-country gaps: y^D_t, π^D_t). The targeting rules and Phillips curves separate additively into world and difference blocks, and Lemma 1 establishes that the capital flow regime affects only the difference block. This decomposition is the analytical device that isolates the role of capital flows.

International trade and macroeconomic dynamics with sanctions

Mon, 01 Jan 0001 00:00:00 +0000

Sanctions are increasingly used as an instrument of economic statecraft, yet their macroeconomic consequences—especially the transitional dynamics and their effects on business cycles—are poorly understood. This paper develops a micro-founded framework combining the intertemporal general-equilibrium structure of standard open-economy macro models with the rich trade-theoretic microfoundations of modern trade theory to study sanctions systematically. In a two-country, two-sector model where Home specializes in differentiated consumption goods (heterogeneous firms, endogenous entry, Melitz-style) and Foreign specializes in homogeneous intermediate goods (Cournot oligopoly in extraction), sanctions—modeled as trade bans and financial restrictions excluding particular Foreign agents—reallocate resources across and within countries, affect production, exchange rates, and welfare, and are shown to inflict larger welfare losses when they target sectors of comparative disadvantage. A central finding is that focusing only on long-run outcomes and overlooking initial transitional dynamics substantially misdirects welfare assessments; sanctions weaken international comovement and fragment markets but, contrary to some claims, leave the structure of business cycles largely intact.

Summary of a forthcoming paper, AI-assisted and human-reviewed. See the linked original for the authoritative claims and full conditions.

In depth

Q1. What is the model structure and what types of sanctions does it capture?

The model is a two-country, two-sector economy: Home has a comparative advantage in differentiated consumption goods (produced by heterogeneous firms with endogenous entry under monopolistic competition, as in Melitz 2003), while Foreign specializes in homogeneous intermediate goods (produced via Cournot competition among a fixed number of upstream firms and processed by a representative distributor). This structure is motivated by the pattern in which Western economies specialize in high-value, firm-entry-intensive industries while sanctioned countries often specialize in commodity production (energy, natural gas). Sanctions are modeled as two distinct instruments: trade bans (restrictions on commerce in goods) and financial restrictions (excluding particular Foreign agents from capital markets). The model accommodates both Ricardian and Melitz-type comparative advantage.

Q2. What are the key results on welfare effects and the role of transitional dynamics?

Sanctions reallocate resources across and within countries, with welfare losses larger when sanctions target sectors of comparative disadvantage rather than sectors of comparative advantage; and focusing only on long-run welfare ignores significant transitional costs that substantially change the total welfare assessment. The model implies that initial transitional dynamics—disruptions to trade flows, entry and exit of firms, exchange rate movements, and adjustment of resource allocation—can be quantitatively important and even dominate long-run effects in welfare calculations. Assessments based solely on steady-state comparisons may therefore produce seriously misleading conclusions about whether and how severely sanctions harm the imposing or target economy.

Q3. How do sanctions affect international comovement and business cycles?

Sanctions weaken international business cycle comovement and fragment markets—reducing the degree to which shocks in one country transmit to the other—but leave the structural properties of business cycles within each country largely intact, in the sense that the cyclical dynamics of output, consumption, and investment retain their qualitative features. This result has policy implications: sanctions can reduce the interdependence of the sanctioned country’s business cycle from the rest of the world (which could be either beneficial or harmful depending on the source of shocks), but cannot fundamentally restructure the domestic cycle.

Q4. What is the baseline application and what general lessons emerge?

While the model’s comparative advantage structure is explicitly motivated by the 2022 Western sanctions against Russia—with intermediate goods interpretable as energy—the framework is designed to be more broadly applicable to other geopolitical conflicts involving sanctioned commodity producers facing differentiated-goods exporters, such as US-China trade tensions. The general lessons are: (1) the sector targeted by sanctions matters greatly for their welfare costs; (2) transitional dynamics are not second-order; (3) financial sanctions operate through different channels than trade bans and should be modeled separately.

Key concepts

comparative disadvantage in sanctions : the paper’s finding that sanctions are more costly when they target goods in which the targeted country has a comparative disadvantage—sectors the country cannot efficiently produce domestically—because those are the sectors where trade provides the highest value and substitution is hardest.

financial restrictions : one of the two types of sanctions modeled, in which particular Foreign agents (firms or sovereign entities) are excluded from international capital markets, distinct from trade bans that restrict commerce in goods.

Unconventional monetary policy spillovers and the (in)convenience of Treasuries

Mon, 01 Jan 0001 00:00:00 +0000

Layer 1 — Overview

Research Question

The paper asks why unconventional monetary policy (UMP) spillovers from the European Central Bank (ECB) to the U.S. Treasury yield curve vary so substantially over time, and whether the time-varying “convenience” of Treasuries — their non-pecuniary premium as the world’s preeminent safe asset — can explain that variation. The core claim is that a declining convenience yield on Treasuries makes them more substitutable with other safe sovereign bonds, thereby amplifying the portfolio-balance channel through which foreign large-scale asset purchases (LSAPs) depress U.S. term premia.

Data and Methodology

The authors use high-frequency identification of ECB monetary policy surprises following Altavilla et al. (2019), defined as the first principal component of intraday changes in 1-, 3-, 6-, 12-, and 24-month euro OIS rates plus 5- and 10-year German and French bond yields, measured in the 10-20 minute window bracketing each ECB decision press conference. Surprises are normalized so that one unit raises the 24-month euro OIS by 10 basis points. The sample runs from March 2001 to December 2023, covering approximately 265-268 ECB announcement dates. U.S. zero-coupon Treasury yields come from Gürkaynak et al. (2007); the yield is decomposed into an expected short-rate path and a term premium using the shadow-rate term structure model (SRTSM) of Wu and Xia (2016). The convenience yield on Treasuries is proxied by the spread between the 10-year Treasury yield and the maturity-matched overnight index swap (OIS) rate, so that a positive (and rising) spread indicates declining convenience. Structural breaks in the convenience yield are identified via the Bai-Perron test.

The empirical strategy has three main components: (i) 700-business-day rolling regressions of Treasury yields and their decomposition on ECB surprises to document time variation; (ii) interaction regressions (following equation 5/9) that condition the ECB shock effect on lagged convenience-yield proxies, net Treasury supply, intermediary balance-sheet constraints (proxied by G10 covered-interest-parity deviations), and inflation-anchoring indicators; and (iii) a policy decomposition following Swanson (2021) that decomposes ECB surprises into “target,” “forward guidance,” and “LSAP” components. These empirical findings are rationalized in a two-country preferred-habitat model, extending Gourinchas, Ray, and Vayanos (in press) (GRV) by allowing the demand-slope parameter governing investor price elasticity to vary with the convenience yield. Functional derivatives and Malliavin calculus are used to characterize dynamic impulse responses to elasticity shifts.

Main Findings with Quantitative Magnitudes

Rising spillovers post-GFC, concentrated at long maturities. Rolling regressions show that ECB-to-U.S. spillovers were statistically indistinguishable from zero during the conventional-policy era but grew significantly after 2010, well before the ECB’s Expanded Asset Purchase Programme (EAPP) launched in 2015 and before “whatever it takes” (summer 2012). Spillovers began to dissipate not when ECB purchases ended (March 2022) but when the Fed announced tapering in November 2021 — consistent with the convenience channel rather than mere co-movement in LSAP volumes. A Bai-Perron test detects five structural breaks in the relationship between ECB surprises and 10-year Treasury yields.
Term-premium dominance, amplified by inconvenient Treasuries. At average convenience-yield levels, a one-standard-deviation ECB loosening shock (lowering the 24-month euro OIS by 10 basis points) reduces the 10-year Treasury yield by approximately 4.4 basis points (column 5, Table 2). When the Treasury convenience yield is one standard deviation below its historical average (i.e., Treasuries are less convenient), the spillover increases by 1.64 basis points, making the total effect approximately 6.1 basis points — a shift from the bottom 20th to below the 12th percentile of the unconditional distribution of daily Treasury yield changes. This amplification operates entirely through the term premium; the expected path of short rates shows no statistically significant sensitivity to the convenience yield interacted with ECB shocks.
Net Treasury supply amplification. Conditional on the net publicly available U.S. debt stock (Treasury debt less Fed holdings, as a percent of GDP), a one-standard-deviation ECB shock at average supply reduces the 10-year yield by approximately 3.9 basis points; when net supply is one standard deviation above its historical average (approximately 7.6 percentage points of GDP), the same shock generates a 5.35 basis-point decline — a 50-percent amplification (Table 5, column 5).
Intermediary constraints amplification. Conditioning on the first principal component of G10 CIP deviations against the dollar (a proxy for intermediary balance-sheet tightness), a CIP deviation one standard deviation above average amplifies the ECB spillover from approximately 3.9 basis points to 6.2 basis points (Table 7).
Inflation anchoring. Periods when inflation expectations lie outside the interquartile range of the historical distribution are associated with larger spillovers to 10-year Treasury yields, an effect that is statistically significant both above the 75th and below the 25th percentile of expectations, with point estimates of the interaction coefficient reaching approximately 5.0-5.3 basis points (Table 6).
Policy asynchronicity. Spillovers are especially pronounced when the Federal Reserve is tightening while the ECB is easing. The rolling regressions show term-premium spillovers become dominant (relative to expected-path spillovers) post-2014, coinciding with U.S. normalization. The calibrated model shows that, during policy asynchronicity combined with lower convenience, the home short-rate tightening is partially offset by capital inflows induced by foreign QE, with the attenuation especially pronounced at intermediate and long maturities and persistent across multiple periods.
Alternative channels ruled out. Horse-race regressions against the VIX, MOVE index, Economic Policy Uncertainty (EPU) index, Monetary Policy Uncertainty (MPU) index, and 30-day EUR/USD spot variance show none of these candidates displaces the convenience channel. Short-rate-risk decompositions (Bundick et al. 2017) and equity-orthogonal risk premium shocks (Leombroni et al. 2021) cannot explain the post-Taper Tantrum timing pattern of rising term-premium spillovers.

Scope Conditions

All empirical results apply to ECB-to-U.S. spillovers; the paper explicitly leaves Bank of England-to-U.K. Gilt spillovers for future work.
The portfolio-balance amplification through convenience is specific to unconventional monetary policy (LSAP shocks); target and forward-guidance components drive spillovers through different channels (expected short-rate path) and do not exhibit the same convenience-contingent amplification.
The mechanism operates through preferred-habitat investors demanding sovereign-grade credit; the Bund convenience yield does not amplify U.S. spillovers, consistent with Bunds being an imperfect representation of the full portfolio requiring substitution under ECB capital-key-based purchases.

Layer 2 — Q&A

Q1: How do the authors measure ECB monetary policy surprises, and why do they prefer this measure?

A1: Surprises are the first principal component of intraday changes in 1-, 3-, 6-, 12-, and 24-month euro OIS rates plus 5- and 10-year German and French bond yields, measured from 10-20 minutes pre-announcement to 10-20 minutes post-press conference. This cross-section of yields is preferred because it summarizes shocks to the overall stance of policy both at and away from the effective lower bound, including effects on different parts of the yield curve. The composite measure therefore subsumes both conventional rate actions and unconventional (LSAP, forward guidance) dimensions. Surprises are normalized so one unit raises the 24-month euro OIS by 10 basis points.

Q2: What is the key empirical fact about the timing of spillover emergence and dissipation?

A2: Rolling regressions show ECB spillovers to U.S. Treasury yields became statistically significant when the rolling window began integrating observations starting in approximately 2010 — substantially before the ECB’s EAPP (2015) and even before “whatever it takes” (summer 2012). Moreover, spillovers began to dissipate not when the ECB’s Pandemic Emergency Purchase Programme ended (March 2022) but when the Fed announced tapering in November 2021. This timing pattern is inconsistent with a simple “both central banks doing QE simultaneously” explanation and instead points to the importance of Federal Reserve balance sheet behavior for the convenience of Treasuries.

Q3: How do the authors decompose the Treasury yield, and what does the decomposition reveal about the channel of transmission?

A3: Following standard term-structure decomposition, the n-year yield equals the expected path of short-term rates over the maturity plus a maturity-specific term premium. Rolling regressions on this decomposition show that term-premium spillovers dominate expected-path spillovers, especially post-2014 when the Federal Reserve is out of sync with other advanced economies. Early ECB UMP spillovers showed a more even mix of expected-path and term-premium effects; later spillovers loaded much more heavily on the term premium. This is consistent with the portfolio balance channel — LSAPs remove duration risk and compress term premia, and this effect transmits internationally.

Q4: How is the convenience yield proxied, and why does the paper use this proxy in particular?

A4: The authors use the spread between the sovereign bond yield and the maturity-matched overnight index swap rate (Y − OIS), expressed so that a larger spread (sovereign yield higher than OIS) reflects less convenience. Prior to the GFC, Treasury yields ran below swap rates (negative spread, high convenience); post-GFC, the spread reversed and turned positive, reflecting deterioration in Treasury specialness. This proxy is preferred because it captures the relative convenience as priced by the marginal investors the model focuses on — those with sovereign credit quality preferences and arbitrageurs — rather than broader measures such as the Treasury-to-corporate spread.

Q5: What is the quantitative impact of convenience yield variation on the size of ECB spillovers to U.S. yields?

A5: In the most conservative specification (Table 2, column 5), an ECB loosening shock that lowers 24-month euro OIS by 10 basis points reduces the 10-year Treasury yield by 4.4 basis points when the convenience yield is at its historical average. When the convenience yield falls one standard deviation below average (Treasuries are less convenient), the spillover increases by 1.64 basis points to approximately 6.1 basis points. A one-standard-deviation change in 10-year Treasury yields in the sample is 5.86 basis points; the 4.4 bp response falls in the bottom 20th percentile of unconditional daily yield changes, while the 6.1 bp response falls below the 12th percentile.

Q6: Does the amplification of spillovers from ECB shocks by Treasury inconvenience operate through the term premium or the expected short-rate path?

A6: The amplification operates entirely through the term premium. In Table 2, columns 7 and 8, the interaction coefficient between the ECB shock and the convenience yield proxy is positive and statistically significant for the 10-year term premium but is not statistically different from zero for the expected path of short rates. The authors interpret this as confirming the portfolio balance channel: displaced Bund investors substitute into Treasuries, raising Treasury prices and compressing term premia, with no mechanical connection to market participants’ updating of expected future Federal Reserve policy rates.

Q7: How does net Treasury supply interact with the size of ECB spillovers?

A7: Net U.S. Treasury supply (debt outstanding as a percent of GDP, less Fed holdings) is strongly positively correlated with the swap spread, confirming the link between supply and convenience. Interaction regressions (Table 5) show that a one-standard-deviation ECB shock at average net supply reduces 10-year yields by 3.9 basis points. When net supply is one standard deviation above average (approximately 7.6 percentage points of GDP), the same shock generates a 5.35 basis-point decline — roughly a 50 percent amplification. The point estimates suggest this operates primarily through term premia, though those interaction coefficients are statistically insignificant in the term premium specification.

Q8: How do intermediary balance-sheet constraints relate to Treasury convenience and ECB spillover amplification?

A8: The authors follow Du, Hébert, and Huber (2023) in using deviations from covered interest parity (CIP) among G10 currencies against the dollar as a proxy for the shadow cost of intermediary balance-sheet constraints. When CIP deviations are at historical average, the ECB spillover to 10-year Treasury yields is approximately 3.9 basis points; when CIP deviations are one standard deviation above average, the spillover rises to approximately 6.2 basis points. The authors also use the plausibly exogenous variation from quarter-end “window dressing” (per Correa, Du, and Liao 2020): LSAP-type ECB surprises landing near quarter-end generate larger spillovers to the term premium, and the further into the quarter an announcement occurs, the larger the LSAP shock’s effect on the term premium — consistent with balance-sheet constraints amplifying the portfolio balance channel.

Q9: What is the theoretical model, and what is the key innovation relative to the baseline GRV framework?

A9: The paper extends the two-country preferred-habitat model of Gourinchas, Ray, and Vayanos (in press), in which segmented investors demand bonds of specific maturities and currencies while capital-constrained global arbitrageurs partially bridge the segmentation. The key innovation is allowing the demand-slope parameter α_j(τ) — which in GRV is fixed and governs how inelastic investors are with respect to price — to vary over time as a function of the convenience yield. When Treasuries are special (high convenience), α_H(τ) is large, demand is inelastic, and foreign shocks have limited pass-through. When convenience falls, α_H(τ) shrinks, demand becomes more elastic, investors reallocate more aggressively in response to yield differentials, and U.S. term premia respond more strongly to ECB purchases. Functional derivatives and Malliavin calculus are used to characterize both instantaneous and dynamic amplification effects.

Q10: What does the calibrated model predict about the maturity structure of spillover amplification?

A10: In the calibration exercise (Figure 4), the elasticity perturbation is modeled as a smooth function (transformed Cauchy distribution) centered at the 10-year maturity, and the ECB QE shock is a purchase concentrated at the 5-year maturity amounting to 10 percent of euro-area GDP. The marginal change in the home yield impulse response (the quantity ∂²_{α_H,b} log P^τ_{Hs}) is positive across nearly all maturities and horizons, but is most pronounced around the 5-year maturity and during the first few periods after the shock — where the ECB purchase profile and the demand perturbation are most closely aligned in tenor. Amplification effects are persistent across horizons due to the dynamic multiplier in Theorem 3.1.

Q11: How does the model rationalize the 2019 yield curve inversion?

A11: In August 2019, the 10-year Treasury yield fell below short-term rates despite a robust domestic labor market, while the Fed was raising rates and the ECB remained accommodative. The model’s asynchronicity exercise (Section 3.3) shows that combining a home short-rate increase with ongoing foreign QE and a contemporaneous decline in Treasury convenience produces attenuated or even reversed yield curve responses. More elastic investors facing a flatter demand curve shift into longer-term Treasuries — whose relative yields remain attractive globally — resulting in a yield-curve inversion driven not by recession expectations but by asymmetric monetary policy and a time-varying convenience premium.

Q12: Do alternative explanations — risk sentiment, policy uncertainty, exchange rate volatility — explain the time variation in ECB spillovers?

A12: No. Horse-race regressions in Table 9 condition the ECB shock on lagged VIX, MOVE index, Economic Policy Uncertainty (Baker et al. 2016), Monetary Policy Uncertainty (Husted et al. 2020), and 30-day EUR/USD spot variance. None of these measures displaces the baseline convenience-yield interaction, which remains statistically significant across all specifications. Elevated EPU is associated with smaller spillovers (consistent with uncertainty impairing substitution), but this does not reduce the magnitude or significance of the convenience-yield interaction. Exchange-rate variance does not alter spillover size. A rolling regression decomposing the term premium into a short-rate-uncertainty component (Bundick et al. 2017) and a residual shows the empirical pattern is more consistent with the residual — not the short-rate-volatility channel. An equity-orthogonal risk premium shock (Leombroni et al. 2021) explains some term premium effects in the early GFC period (2008-2012) but cannot rationalize the post-Taper Tantrum pattern of growing term-premium spillovers.

Q13: How does the Swanson (2021) decomposition confirm the portfolio balance channel?

A13: Following Swanson (2021), the authors decompose ECB surprises into a “target surprise” (change in 3-month OIS futures), a “forward guidance surprise” (residual from projecting 24-month futures onto the target surprise), and an “LSAP surprise” (residual from projecting French and German 10-year bond yields onto target and forward guidance). In the full sample (Table 3), LSAP shocks drive spillovers to U.S. yields exclusively at higher maturities and exclusively through the term premium; they have no statistically significant impact on the expected path of short rates. Conditioning LSAP shocks on the convenience yield (Table 4, panel c) shows that it is specifically LSAP-type announcements combined with Treasury inconvenience that generate larger medium- and long-term term-premium spillovers, confirming the portfolio balance mechanism.

Q14: What are the implications for fiscal and monetary policy?

A14: The paper argues that the persistently low long-term rates and yield curve inversions observed between the GFC and the COVID-19 pandemic were driven partly by ECB LSAPs amplified by U.S. quantitative tightening, which increased net Treasury supply, reduced Fed absorption, constrained dealer balance sheets, and lowered Treasury convenience. Simultaneously, U.S. monetary tightening raised short-term rates while ongoing ECB easing depressed long rates, reshaping the yield curve in a manner consistent with the model. More broadly, the effectiveness of conventional domestic monetary policy tightening is attenuated when the convenience yield is compressed and foreign QE is ongoing — not because the short rate fails to move, but because more elastic investors reallocate around it. This suggests policy asynchronicity, combined with declining convenience, creates a constraint on monetary independence that may require more forceful or coordinated policy action.

Key Concepts

Convenience yield (Treasury convenience premium) The non-pecuniary value that investors derive from holding U.S. Treasury securities over and above cash flows and credit risk — arising from their deep and liquid markets, broad regulatory compatibility, high-quality collateral function, and reserve-currency status. Operationalized in this paper as the spread between the n-year Treasury yield and the maturity-matched overnight index swap (OIS) rate; a positive and rising spread indicates declining convenience, not increasing yield risk.

Portfolio balance channel (of unconventional monetary policy transmission) The mechanism by which large-scale asset purchases by one central bank displace investors from their target allocations, inducing them to substitute into other assets — including foreign sovereign bonds — thereby compressing yields and term premia in those markets. Distinguished from the signaling/expected-path channel in that it operates through changes in duration risk (term premia) rather than revisions to expected future short rates, and is unique to UMP because it targets long-duration assets.

Preferred habitat investors Investors with persistent, institutionally determined demand for bonds of specific maturities and issuers (e.g., insurance companies, pension funds), arising from regulatory constraints, risk management practices, or balance sheet matching. Their demand is modeled as relatively price-inelastic when assets command a convenience premium, and more elastic when that premium erodes.

Demand-slope parameter α_j(τ) In the extended GRV preferred-habitat model, the parameter governing the price elasticity of preferred-habitat investor demand for country-j bonds of maturity τ. Large values imply inelastic demand (strong habitat preferences), small values imply elastic demand and greater cross-border substitutability. The paper’s key innovation is treating this parameter as time-varying — specifically, as a function of the observed Treasury convenience yield rather than a fixed structural constant.

Policy asynchronicity The condition in which the Federal Reserve is tightening monetary policy (raising rates or conducting quantitative tightening) while other advanced-economy central banks (specifically the ECB) are simultaneously easing through LSAPs. The paper argues that asynchronicity interacts with a declining convenience yield to amplify ECB spillovers to U.S. term premia and attenuate the effectiveness of Federal Reserve tightening at the long end of the yield curve.

Swap spread (as inconvenience proxy) The spread of the sovereign bond yield over the maturity-matched OIS rate (Y − OIS). Expressed so that a larger positive value indicates greater Treasury inconvenience. Prior to the GFC, 10-year Treasury yields ran below swap rates (negative spread); post-GFC, this relationship reversed, with the spread turning persistently positive and exhibiting structural breaks consistent with Bai-Perron tests.

Exorbitant privilege The benefit the United States accrues from the global dominance of its sovereign debt and currency, which structurally insulates U.S. financial markets from foreign monetary policy shocks through inelastic global demand for Treasuries. The paper argues this insulation is not structural but endogenous and state-dependent: erosion of exorbitant privilege — operationalized as a declining convenience yield — substantially increases U.S. vulnerability to foreign monetary shocks.

Gâteaux/Malliavin functional derivative (as used in the model) Mathematical tools used to characterize how the impulse response function of the yield curve to policy shocks changes when the demand-slope parameter α_k(τ) is perturbed. The mixed Gâteaux differential ∂²_{α_k,b} log P^(τ)_{js} captures both the instantaneous amplification (direct pass-through increase) and the intertemporal propagation (dynamic multiplier) of a foreign policy shock under lower convenience, enabling a tractable decomposition of state-contingent spillover magnitudes across maturities and horizons.